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I want to simulate mixing two different fluids with two different inlets and one outlet in COMSOL. Which physics are suitable for this simulation? Should I use "Laminar flow" and "Transport of Dilluted apecies" or "Multiphase flow (laminar flow+level set)???
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You can use transport of dilute species (TDS) module in COMSOL, when your fluid mixture is homogeneous in nature in order to have an effective mixing index, while in the case of heterogeneous mix it's good to use any of multiphase model/module in COMSOL (Laminar flow or Creeping flow based on the Reynold's number).
When it comes to the physics to be added for numerical computation, I prefer Phase field over Level Set as the diffusion part dominates in the case of Level Set and few a times based on case to case the results varies a lot when tried with different cases. Phase Field is a better option.
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I am simulating Ethanol flow boiling through a horizontal rectangular microchannel using Multiphase VOF model (evaporation-Condensation Mechanism) to simulate annular flow based on experimental data. I getting a lot of errors in the simulation and some times solution diverge.
Is there any tutorials or any references that would help for this?
Any recommendations for time step size needed to capture the phase change?
Thank you
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If you are using the explicit VOF model, you should choose your time step in a way that Courant number is less than 1.
In my simulations I used 1e-8 s, and I did not face any problem.
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What do we mean by sharp and diffused interface model in the context of multiphase flows?
Kindly clarify the difference with the help of famous methods, i.e., in which category do they fall: phase field method, LBM, LS, VOF, CLSVOF, etc.?
Which one should be preferred and why?
It is kindly requested, if you can, to help with the references to support your answer.
Best regards.
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In the context of multiphase flows, the terms sharp interface model and diffused interface model refer to how the interface between two immiscible phases (e.g., liquid and gas) is represented.
Sharp Interface Model
  • In this model, the interface is treated as a discontinuity with negligible or no thickness.
  • The fluid properties (e.g., density, viscosity) change abruptly across the interface, and the interfacial dynamics (e.g., surface tension) are explicitly computed at the interface.
Famous Methods in this Category:
  1. Level-Set (LS) Method: Represents the interface as the zero level of a signed distance function. The interface is tracked sharply but requires reinitialization to maintain a proper distance function.
  2. Volume of Fluid (VOF) Method: Tracks the volume fraction of a fluid in each computational cell. The interface is reconstructed (e.g., PLIC) and remains sharp, although reconstruction errors may introduce some diffusion.
  3. Coupled Level-Set and VOF (CLSVOF):Combines the accuracy of LS for smooth interface representation with VOF's mass conservation. Maintains a sharp interface with better mass conservation.
Diffused Interface Model
  • Here, the interface is represented as a continuous transition region where fluid properties vary smoothly over a finite thickness.
  • The interface dynamics are modeled by additional equations, often involving a phase field variable.
Famous Methods in this Category:
  1. Phase-Field Method: Introduces an order parameter (e.g., concentration or phase variable) that varies smoothly between the phases. Solves a Cahn-Hilliard or Allen-Cahn equation for the phase variable. Naturally captures topological changes (e.g., coalescence, breakup) but requires fine resolution to resolve the interface width.
  2. Lattice Boltzmann Method (LBM): Can implement both sharp and diffuse interface approaches, but it is commonly used with phase-field-like approaches for diffuse interfaces. Handles complex interfacial dynamics, especially for flows involving micro/nano scales.
Which Should Be Preferred and Why?
The choice depends on application requirements:
  1. Sharp Interface Methods: Preferable when high accuracy in interface shape and dynamics is critical (e.g., droplet collisions, wave breaking). Suitable for macroscale flows with well-defined interfaces. Methods: VOF and CLSVOF are common for mass conservation; LS is chosen for smoother interfaces.
  2. Diffuse Interface Methods: Ideal for flows where topology changes (e.g., coalescence, breakup) occur frequently and need automatic handling. Suitable for microscale flows, flows with thermal or solutal effects, or phase-change problems. Methods: Phase-Field and LBM for interfacial transport processes.
Practical Preference:
  • For industrial applications requiring mass conservation and sharp interfaces (e.g., multiphase simulations in aerospace or automotive sectors), CLSVOF is often preferred.
  • For flows involving interfacial instabilities or complex phenomena like emulsification, Phase-Field or LBM may be more efficient.
Choosing the best model also depends on the available computational resources and the physics of the problem being simulated.
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Can somebody explain the difference in two terms : Interface tracking methods, and interface capturing methods in the context of multiphase flow modelling?
There are multiple methods, like, phase field model, level set, which categories do they fall in and why? if someone can help clarify this. please.
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In the context of multiphase flow modeling, interface tracking and interface capturing methods are two distinct approaches to handling the evolution of interfaces between different phases (e.g., liquid-liquid, liquid-gas). Here's an explanation of each and where methods like the phase-field model and level-set method fit in:
Interface Tracking Methods
  • Definition: Interface tracking methods explicitly track the location of the interface by using computational elements (grids, markers, or particles) that follow the interface as it evolves.
  • Key Features: The interface is a sharp boundary. The computational mesh or marker adapts to follow the interface. Examples: Lagrangian Methods: The interface is explicitly represented by marker points or meshes that move with the fluid flow. Front Tracking Methods: A separate mesh or set of points tracks the interface, which is then projected onto the computational grid.
  • Advantages: Precise interface representation. Accurate modeling of sharp discontinuities in properties like density or viscosity.
  • Disadvantages: Challenging for complex interface topologies (e.g., merging or splitting of interfaces). Computationally intensive due to the need for mesh adaptation or marker handling.
Interface Capturing Methods
  • Definition: Interface capturing methods implicitly represent the interface on a fixed computational grid without explicitly tracking its location. Instead, the interface is reconstructed or identified using a continuous field.
  • Key Features: The interface is not a sharp boundary but is represented by a transition zone. The governing equations for the field are solved across the entire domain, including the interface. Examples: Volume-of-Fluid (VOF): Tracks the volume fraction of a phase in each grid cell. Level-Set Method: Uses a signed distance function to represent the interface location. Phase-Field Method: Represents the interface as a diffuse region where an order parameter (like a concentration or phase field) transitions smoothly between phases.
  • Advantages: Handles complex topologies (e.g., break-up or coalescence) naturally. Suitable for large deformations of the interface.
  • Disadvantages: Less precise representation of the interface. Diffusive nature can blur sharp interfaces if not well-resolved.
Classification of Specific Methods
  1. Level-Set Method Category: Interface capturing. Why: The interface is represented by a signed distance function (zero level-set = interface), and the function is evolved using advection equations. The interface is reconstructed implicitly on a fixed grid.
  2. Phase-Field Model Category: Interface capturing. Why: The interface is represented by a smooth transition of an order parameter (e.g., concentration or phase indicator) governed by coupled partial differential equations (e.g., Cahn-Hilliard or Allen-Cahn equations). The interface is diffuse, and the width is controlled by model parameters.
  3. VOF (Volume of Fluid) Category: Interface capturing. Why: Tracks the volume fraction of the fluid in each computational cell and reconstructs the interface implicitly based on these fractions.
  4. Front Tracking Category: Interface tracking. Why: Uses marker points or meshes that explicitly follow the motion of the interface.
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I am currently running a multiphase CFD simulation in ANSYS Fluent, involving liquid, gas, and solid phases with a moving bed of 3D-printed biocarriers in a water tank. The simulation frequently encounters the error "Negative Cell Volume Detected", which causes it to terminate prematurely.
The simulation setup includes:
  • A refined, unstructured mesh.
  • No-slip boundary conditions at the walls.
  • An opening condition at the top of the domain as an outlet.
  • Smooth symmetry planes and inflation layers near the walls.
Despite adjusting mesh refinement and time-stepping, the error persists. What could be causing this issue, and what are the best practices for resolving it, particularly when dealing with complex geometries and multiphase flow?
Any advice on improving mesh quality, setting numerical schemes, or adjusting solver parameters would be greatly appreciated.
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The negative cell volume in ANSYS Fluent is related to dynamic mesh whether the flow is single phase or multiphase. You have to double-check the dynamic mesh model and settings and try to reduce the time step size. If there is a boundary layer adjacent to the moving wall (object) you have to check the option that excludes the boundary layer from remeshing.
Kind regards,
Ashkan
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Hello,
I am running a 3-D transient multiphase flow simulation for droplet coalescence over the hydrophobic substrate using the VOF model in the fluent 2020R2. To decrease the computational load, I am using volume fraction gradient-based mesh adaptation and adaptive time step advancement tool to model the coalescence. The following issues have been found while running the simulation.
Case _1.  When I am starting transient simulation at the zeroth time step and run it continuously up to any time step, the gradient-based mesh adaptation works uniformly.
For example, if I am running a transient simulation from zero to 330-time step (as shown in the attachment  A_Uniform Mesh_ time 330). The mesh adaption works smoothly throughout the domain.
I am looking for a solution for Case _2. Because currently, I am working on a problem, where it is required to restart the simulation at any time step and to simulate it for further time steps.
Here I am attaching all the details used to model the droplet coalescence.
I have defined a volume fraction gradient over the flow domain. As shown in the figure
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Hi, I wonder why you do not define the coarsing criterion in Fig. 4?
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11
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Modeling and simulation of the electrospinning process
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https://www.sciencedirect.com › article › abs › pii
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2024 3rd International Conference on Materials Engineering and Applied Mechanics (ICMEAAE 2024) will be held from March 15 to 17, 2024 in Changsha, China.
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Dear Sarabjeet KaurFor more details please visit the conference website:
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I am currently engaged in research on hydrogen storage and migration, and I am exploring the application of the lattice Boltzmann method to simulate multiphase flow within porous media formations. This is a new area of study for me, and I have come across numerous LBM models that have been implemented. However, I am uncertain about which model would be most suitable for my specific case, which involves a significant viscosity ratio and density ratio due to simulating brine and hydrogen. If anyone has expertise in this field or any information regarding the lattice Boltzmann method for fluid flow, I would greatly appreciate your input.
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Thanks Suresh Ahuja
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I start working on Multiphase flow simulation of bubbly flow using mixture model but I have some problems working with this model.
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Hope these files are helpful to you.
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I need two model heat exhanger between air and water. But air will be admitted in liquid state at negative temperature and on leaving the heat exchanger it should be in gaseous state.
In this problem two fluids are involved
Water
Air
Once again Air has enter in
Liquid state
On transferring heat from water it has to be converted to
Vapour.
I'm aware interphasechangefoam for phase change and CHTMultiregionfoam for two fluids. But in this case two fluids are involved. In this two fluid, one fluid has to undergo phase change.
Regards
Dr. Ijaz Fazil.
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Hi,
I guess you could chose one of the two fluid inter solvers. They are based on Volume of Fluid and easy to apply. But you should really take care about cell resolution for good results of course. To take account for natural convection just apply boussinesq or polynomial thermophysicalProps. For polynomials you need to fit function coefficients according to your const. Pressure and temperature range. Unfortunately it can happen, that property calculation is not that precise.
On the other hand it is possible to chose euler solvers instead of inter solvers of course. But in my opinion you need really deep knowledge about all those empirical coefficients.
Hope that helps.
Regards David
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Multiphase flow meters (MPFMS) are used across the industry to measure production fluids (oil, water, and gas) to perform the allocation per well. However, some of the fields/reservoirs have seawater injection, which changes the composition of produced water over time. At the beginning of the life field will have 100% formation water (higher salinity) and over the time the mixing with sea water will reduce the overall salinity until you have 100% seawater. The 81 keV and 32 keV are the energy bands from Gamma-ray emitted from a radioactive source of Barium 133 used in the MPFMs.
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This may help you:
For mixtures of differing composition you can follow the procedure near the end of this:
For elements of "similar" Z, the attenuation coeff is similar, so the values will scale roughly with density so it seems that telling one salinity from another might be quite difficult.
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Hi all,
I am currently working on simulating a water jet problem, where water is injected from the left boundary and exits the domain through the right boundary. However, I am facing a challenge of keeping both momentum and mass conservation at the same time. In order to ensure mass conservation in the scenario where a single two-dimensional jet evolves into multiple droplets, it is necessary to enforce the condition that the outlet flux, represented by the product of the cross-sectional area of the droplets (S2) and their velocity (u2), is equal to the inlet flux, represented by the product of the initial cross-sectional area of the jet (S1) and its velocity (u1). Since S2 is typically greater than S1, it follows that u2 must be smaller than u1 to maintain mass conservation. However, this approach alone does not guarantee momentum conservation.
ps: I am using my own code for the simulation and it is an incompressible flow solver, which has been validated in many benchmark cases. The physical properties in my code jump across the interface without any diffusion.
Best regards,
Min Lu
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Hi
It may say that you do the simulation with your own code, or with Fluent or CFX?
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I want to simulate mixing two fluids with different inlets and velocities in COMSOL. I used "Laminar Flow" and "Transport of Diluted Species" physics to do it, and my problem is that I cannot select both fluids for my domain. I have two fluids and one domain for mixing. How can I do it? Should I use "Multiphase Flow" physic?
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Yes, you have to define a multi-phase model, e.g., VOF or Euler-Euler.
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Hello everyone,
I'm working with ANSYS FLUENT and trying to simulate a reaction in Multiphase flow, using Arrhenius equation. I'm finding it hard to literally understand/interpret the meaning of "normalization temperature" and "kick-off temperature" (please view the attached file). I will be very grateful for your help.
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Dear Salman,
This is very much appreciated.
Many thanks.
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Hi,
I am modelling an alkaline water electrolyzer by using multiphase flow and species transport physics.
I am confused between gas and bubbles terms. From multiphase flow I can simulate the gas and liquid phase. While, with species transport I can simulate gas concentration in liquid and bubble nucleation.
Is bubble nucleation indirectly tells about gas region?
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The difference is in the morphology of the flow:
bubbly flow - gaseous and liquid phase are NOT mixed on a molecular level, but the gaseous phase forms bubbles as macroscopic inclusions into a continuous liquid phase. E.g. Air bubbles of 2mm size in water.
flow of a mixture - the gaseous and liquid phase are mixed on a molecular level. No macroscopic inclusions of either of the two phases can be observed. E.g. dissolved CO2 in water.
Bubble nucleation - the process of forming first macroscopic bubbles from a continuously dissolved gaseous phase. E.g. you open a pressurized bottle of mineral water with gas. In the first moment, there is only clear water visible. But after some miliseconds first bubbles appear and this process (e.g. if you shake the bottle) can become pretty "violent". This is called nucleation and bubble growth by depressurization. Other mechanisms of nucleation are possible.
Regards,
Dr. Th. Frank.
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Hi all,
I am going to use either Ansys CFX or Ansys Fluent solver to simulate flow past a semi-submerged rectangular cylinder, as shown in Fig. 1. The main goal here is to achieve an accurate prediction of pressure distribution over the cylinder, which seems to be particularly reliant on the capability of the CFD model to predict the separation and the reattachment of the flow correctly. I would appreciate any tips regarding the following questions.
Q1. How important is the choice of the turbulence model? Which models are superior? Could the flow be modelled as being laminar at all?
Q2. How important is the approach to the free surface? Could the free surface be modelled as a free-slip wall to reduce computational costs? Is it necessary to precisely track the free surface using the VOF model for this study?
Q3. What are the most appropriate boundary conditions for the simulation?
Q4. Which is more suitable for this problem? CFX or Fluent?
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If the size t is less than 8-12 distances to the bottom surface, the drag force will be determined, among other things, by the added masses of the liquid reflected from the bottom surface. If this is not important, then in the model you need to specify a distance of more than 12.
The number of wall layers is enough 5.
From above on a free surface, the wind has a speed and direction?
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Has anyone tried modelling multiphase flow (interFoam solver) using LRR or SSG turbulence closure in OpenFOAM? I want to discuss about it.
Subhojit
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Yes, and it does not show good precision.
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Using COMSOL software to realize the numerical simulation of multiphase flow problem, in the field of microfluidic research, how to realize the simulation of the dynamic contact angle of droplets?
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Ziyi Wu, Thank you, I know what you said. But my question is about how to simulate dynamic contact angle instead of static contact angle.
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I am performing a simulation in Ansys fluent using multiphase flow settings for two phase flow problem and with out multiphase flow settings for single phase flow. The results differs heavily and huge enhancements in multiphase flow.
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THE ENHANCEMENT OF HEAT TRANSFER BY TWO PHASE OR MULTIPLE IS MORE THAN SINGLE PHASE
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Hi dears I encounter some problems in growth rate udf and I share them. I hope someone help me out. I have a growth rate in population balance which depends on the diameter: G(L)=(Rp*L0*L0*L0)/(3*ro*di*di*di) Which L0 is initial diameter and di is next diameter due the growth. I set initial diameter, but next step time initial diameter will change and I don't know how udf can recognize new diameter. Moreover, how I can set di?
bests
Mohammadhossein
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Without more details, I only may speak about the phenomenological aspects that may be verified. (i) When one applies User Defined Function (UDF) this should not contradict the mass conservation of the dispersed phase (ii) the initial diameter would depend on many factors: surface tension, turbulence, injection device...References on dispersed turbulent flows are available on the following research projects: https://www.researchgate.net/project/Single-Phase-and-Multiphase-Turbulent-Flows-SMTF-in-Nature-and-Engineering-Applications https://www.researchgate.net/project/Interfacial-Transfer-Closure-for-Eulerian-Eulerian-Two-Fluid-Modeling https://www.researchgate.net/project/Turbulence-Closure-for-Eulerian-Eulerian-Two-Fluid-Models
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Hello all,
I intend to perform a CFD analysis of the well-known bridge pier scour problem. I am considering two software packages for this purpose: Ansys Fluent and Flow 3D. I am trying to explore the pros and cons of each package for my case.
I would appreciate your comments on any of the following.
1- In order to make a sound comparison, I need to understand the modelling details implemented in Flow 3D, especially a clear description of the way sediment transport is modelled and coupled with the hydrodynamic solver, and how the interphase interaction is realized. Despite lots of research, I have not been able to find detailed information on this.
2- Any study on comparing the performance of these two packages for bridge pier scour problem.
Regards,
Armin
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I have three suggestions for you:
1- Check the below link:
As this topic is popular in our country, I am sure you can find different Ph.D. and M.Sc. theses in Iranian universities.
2- Ask your question in CFD online forums:
3- If you could not find your answer about bridge piers, search for other hydraulic structures (for example, spur dikes) and use their information.
Good luck,
Maryam
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The pressure boundary in multiphase simulations is important. A widely used pressure boundary may be to enforce the normal gradient of the pressure to be zero. However, this is not always physical and the accuracy is poor. How to define the pressure boundary more physically, in particular, the partially wetting boundary condition is involved together. Have any suggestions?
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More information is needed to answer this question. Basically, even in single-phase flows, the normal gradient of the pressure is almost zero only in parallel or almost-parallel vertical laminar flows. The average pressure is "permeated" by turbulence even in 2D parallel flows. When it comes to two-phase flows and within the framework of RANS modeling using Eulerian-Eulerian two-fluid models closure is needed in order to express the pressure in one phase as a function of that of the second phase. The simplest considers that the two pressures are equal in the absence of surface tension. See references within the research projects: https://www.researchgate.net/project/Single-Phase-and-Multiphase-Turbulent-Flows-SMTF-in-Nature-and-Engineering-Applications https://www.researchgate.net/project/Interfacial-Transfer-Closure-for-Eulerian-Eulerian-Two-Fluid-Modeling https://www.researchgate.net/project/Turbulence-Closure-for-Eulerian-Eulerian-Two-Fluid-Models
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Hello all,
Source terms have been known to cause reliability issues in numerical methods affecting therein convergence and accuracy. I am currently facing a similar challenge when trying to solve a Poisson equation with a non-zero divergence velocity field. The source term that I am working which is a cavitation source term dependent on local value of pressure.
For the most part, linearizing that source term seems to solve the issue in the literature however even with linearization my Poisson equation does not converge, and even when it does, the solution is inaccurate and often oscillatory.
Any input from the experts would be helpful
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Noted professor Stam Nicolis , I will keep that in mind. Thanks for your time and help!
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In Ansys Fluent, there is an option to solve your multiphase flow problem using either Eulerian, Mixture or VOF models. Can we analyze phase change of water to steam using VOF?
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Yes you can, First you have to specify the type of material in the fluid part and then select the flow type again with the Multiphase (Volume of Fluid)
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Hello,
I'm currently working on modelling multiphase flow with phase field, I'm using the PDE toolbox to simulate the phase field equation.
As described in this article: https://www.comsol.com/paper/adaptive-mesh-refinement-quantitative-computation-of-a-rising-bubble-using-comso-64111 AMR should lead to to massivley improved performance. But I'm not able to reproduce the results presented in the article. Does anyone has experience in time dependent AMR for multiphase flow in Comsol and could give me a hint what are the proper paramater in the AMR solver of COMSOL?
Thanks a lot.
Best regards,
Lukas
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We have tried AMR for multiphase flow with phase-field in the past. Usually, refinement is dependent on the phase-field parameter and you can control the number of refinements in a given time scale of simulations. You can refer to the following articles for more information on the implementation of AMR in the Comsol phase field.
1) Yue, P., Zhou, C., Feng, J. J., Ollivier-Gooch, C. F. and Hu, H. H., "Phase-field simulations of interfacial dynamics in viscoelastic fluids using finite elements with adaptive meshing," Journal of Computational Physics, 2006, v. 219, n. 1, pp. 47-67.
2) Zhou, C., Yue, P., Feng, J. J., Ollivier-Gooch, C. F. and Hu, H. H., "3D phase-field simulations of interfacial dynamics in Newtonian and viscoelastic fluids," Journal of Computational Physics, 2010, v. 229, n. 2, pp. 498-511.
3) Yue, P., Feng, J. J., Liu, C. and Shen, J., "A diffuse-interface method for simulating two-phase flows of complex fluids," Journal of Fluid Mechanics, 2004, v. 515, pp. 293-317.
4) Yue, P., Zhou, C. and Feng, J. J., "Spontaneous shrinkage of drops and mass conservation in phase-field simulations," Journal of Computational Physics, 2007, v. 223, n. 1, pp. 1-9.
5) Yue, P., Zhou, C. and Feng, J. J., "Sharp-interface limit of the Cahn–Hilliard model for moving contact lines," Journal of Fluid Mechanics, 2010, v. 645, pp. 279-294.
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I benchmarked my Shan-Chen Multiphase LB model using the droplet test; further I am trying to shear deformation of the droplet under moving parallel plates (in opposite directions). I would like to plot Capillary number v/s Deformation for the validation, but I am bit skeptical about the deformation and Ca calculations and hence to check for the Re of my simulation.
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I doubt you gonna get reliable results studying droplet deformation in liquid-liquid dispersed flow by means of simulations with commercial codes. The phenomena involved is too complex. Droplets break and coalesce under simultaneous population and wall effects, also depending on the interfacial tension between phases as well as on the local pressure (assuming constant temperature). For a given pair of fluids, the relative velocity between droplets and continuous phase depends on size and shape of droplets. The relative velocity also induces pairs of vortices rotating in opposite directions inside droplets (conservation of angular momentum). These may cooperate for the droplet breakage.
Even though it may be well outside your research scope, experiments are required if you want reliable data.
I guess a little craft hability is required. Build a mechanical device where small parallel glass plates (same width and thickness as those used in microscopy) are pulled along in opposite directions, similar to your Couette rheometer. Clearly the experiment will be 2D. The small gap between plates would be filled with the liquid-liquid dispersion. Some sort of rail system will be required for guiding the sliding plates. The plates could be pulled with the help of an electrical DC electrical motor with variable rpm and a system of pulleys. Make photograph/film from above. Ah, include my name on the Patent application (laugh).
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Hello guys,
I would like to know whether I could simulate three phases or three liquids in the VOF model in Ansys Fluent. If we can, then how can we do it?
One is Air and the other two liquids are polymers. Any suggestions are highly appreciated!
Thank you
Rajesh
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Resources and academic tools on turbulent single-phase and multiphase flows in industrial facilities and in natural environments
SINGLE PHASE AND MULTIPHASE TURBULENT FLOWS (SMTF) IN NATURE AND ENGINEERING APPLICATIONS | Jamel Chahed | 3 publications | Research Project (researchgate.net)
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Hello experts, I am a new to ANSYS fluent. Currently, I am facing some issues in my problem which is on multiphase flows. I have used VOF method in Ansys fluent but during my simulation I am unable to incorporate the material properties of my inlet fluids. Can anyone help me to know the process of incorporating more than two fluids in such multiphase flow analysis in Fluent ? Here I am attaching the screenshot of the procedure of applying material properties I have been using. I am confused whether the procedure I am applying is correct.
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I refer you to two discussions which bear on the two problems of Eulerian two-fluid models closures: Turbulence and momentum interfacial transfer:
(6) Turbulence Closure for Two-Fluid RANS Modeling (researchgate.net)
(6) Interfacial Transfer Closure for Two-Fluid RANS Modeling (researchgate.net)
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Hi all,
The case I want to simulate includes a porous media baffle, with water on the left side and no water on the right. I want to simulate the process that water on the left flows into the porous media and then flows into the right side.
In my simulatioin, the seepage velocity (from the soil to the fluid domain) at the interface is calculated by solid part. Then, there should be more water at the interface in fluid domain. I’ve managed to couple the seepage velocity at the interface in OF, but how could I add the water due to the seepage according to the velocity at the interface? Could anyone please give me any hints?
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I refer you to two discussions which bear on the two problems of Eulerian two-fluid models closures: Turbulence and momentum interfacial transfer:
(6) Turbulence Closure for Two-Fluid RANS Modeling (researchgate.net)
(6) Interfacial Transfer Closure for Two-Fluid RANS Modeling (researchgate.net)
Look forward to exchanges on these topics
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Hello Everyone, I am trying to simulate a Y shaped channel using VOF method in Ansys Fluent. Discretization of the model has been done. Inlet velocities of both dispersed and continuous phase are calculated using Capillary Numbers. I have considered no slip boundary condition at domain wall. Hereunder is the method I have applied while performing the simulation: Method- a)pressure velocity coupling scheme= coupled with vof b) Discretization method- Green gauss cell discretization method c) Pressure-PRESTO d)Momentum-Second order upwind e) Volume fraction-compressive f) Transient formulation-Bounded second order implicit Provided a suitable Residual of 10^-6, Time step size- 100 and  Max iterations/step size-20. My objective is to form a Janus Droplet. But droplet is forming but no janus droplet formation took place applying this methodology. Can anyone please throw a light on where I am doing wrong or is there any other process to form a Janus droplet.
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I'm looking for publications regarding the Two-Relaxation Time Lattice Boltzmann Method's forcing schemes without passing through the Multi-Relaxation Time's full procedures
I'm specifically searching for the TRT implementation of Shan-Chen forcing scheme (ueq=u+tau*F/Rho)
Any contribution is highly appreciated
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Almost a year later, but anyways:
I wrote together with someone else an article that probably suits your needs:
Preprint is on researchgate.
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hi.
I have a problem in my simulation work. I use flow-3d for simulating a surface vortex with an air core in a pipe-tank system. I have been successful simulating the vortex with 1cm mesh size, but I haven't been able to see the air core. Due to this problem I had to had to use finer mesh with size of 0.6cm.
When using finer mesh ,my streamlines of the near surface particles change dramatically in comparison with the streamlines I had when using coarser mesh with 1cm mesh cell size.
In coarser mesh my streamlines are strongly sucked and driven into my pipe but when i reduce my mesh cell to 0.6cm, with exactly the same setup my streamline suddenly get shorter and incomplete. It seems that after changing the mesh size the flow of water in to the pipe is not enough strong to create the enough suction for near surface particles of water and due to this there i see no air entrainment afterward.
I will upload the photos of my streamlines in both conditions, I'll be so delightful if anyone can tell what is the cause of this problem I have and how I can solve it?
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Giuseppe Altieri thanks very much for your answer
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Dear. all,
I performed a direct numerical simulation of multiphase flow in a porous medium (considering surface tension).
How to determine the relative permeability?
In Wikipedia, it was not mentioned which flux (inlet or outlet?), how to calculate the gradient pressure for each phase?
What if I have changing viscosity (e.g. due to the temperature)
BR,
Evgenii
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In my limited understanding, i utilized a steady state model to calculate the permeability of certain structures (resembling metallic foam). The simple way that I used to adopt was to apply a known pressure difference at the inlet and outlet, and obtain volume flow rate through post processing. This would simply give you the permeability. Ofcourse, the higher the volume flow rate, the more permeable the porous medium shall be. However, under transient conditions and using variable viscosity, the problem gets much more complicated. Nonetheless, steady state isothermal condition can be a good starting point and may give you a reasonably accurate ball park value.
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Hello everyone, hope all is good.
I want to analyse multi-phase fluid flow through pipe, which software is best to do so ?
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Go for Ansys CFX or COMSOL.
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Dear All,
I have been working on multiphase flow through a complex geometry having porosity 0.25. I have patched it with oil and high-salinity brine. At the inlet I am flowing low-salinity brine. It is a pressure based, laminar, species transport without chemical reaction problem.
I am opting for a VOF steady state simulation since I wanted to pressure drop at water breakthrough and volume fraction of residual oil.
Even after 3500 iterations the solution is not converging even after using a coupled solver.
Please guide.
Thanks in advance
Dr. Shilpa Nandwani
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Dear Shilpa,
the source of the problem can be varied from one model to another. However, overall, coupling process of solute transport with the phase flow behavior can cause such issue. The associated factors, however, can be changed from traditional factors (i.e. grid size and time step) to non-conventional factors ( e.g. Effective concentration and the shape of rel perms). Also the solution type of the numerical scheme can be another source of such issue (e.g. fully coupled schems causes convergence issue more than decoupled scheme). See SPE-192074-MS and
Al-Ibadi, H., Stephen, K., & Mackay, E. (2020). Pulse Generation and Propagation in the Numerical Solution of Low Salinity Water Flooding. Journal of Petroleum Science and Engineering, 108151.
Hasan
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The electrical tomography can be utilized to calculate the solid concentration or gas holdup in aqueous based multiphase flows. However, there usually exists a strong nonlinear relationship between the solid concentration and tomographic image. Is there any effective way to handle this problem?
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Within the classical framework, one can minimize the error between measurements and calculated values, in function of the multiphase electrical properties. There are different optimization algorithms which deal with non-linearity, with the most popular being Gauss-Newton, Simulated Annealing and Kalman filtering. Of these three, Simulated Annealing requires a large processing time and Kalman filtering may be suitable for real time (depending on other aspects).
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I have this problem when i  take geometry in fluent .Model Information is incompatible with incoming mesh. How to resolve it?
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Right click 'Setup' and press reset. This will force you to start everything after the updated mesh from scratch. Don't bother looking for the error.
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In my Simulation I have a Filter with a multiphase flow (Air and Oil). Now in my report the pressure drop (Area weighted Average) Static-Pressure-Mixture is higher than the total pressure drop (Air selected).
Because Total Pressure is the sum of static and dynamic pressure, the static pressure normally cannot be higher than the total. Does anybody have an explanation for that?
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Well did you got the answer ?
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Hello all!
I am trying to simulate a problem where a drop deforms under the given flowing conditions of ambient fluid. I want to have a coarse grid throughout the domain, but different levels of refinement should be present near the interface. I want the mesh to be refined after every few timesteps. Is there any predefined function in Fluent to implement this or do I need to use a UDF?
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Don't know with fluent but with Hypermesh mesh refinement can be achieved.
These videos will help to learn 2D and 3D mesh transition techniques.
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I have a class project where we are vacuuming wet sand and my team wishes to know how fast the vacuum container would fill with the wet sand. I am unsure how to compute the multiphase flow because I have no experience in multiphase flow. The calculation can be fairly rough, but I don't want to use a model that simply doesn't work. I have seen there are a number of methods but cannot decide which to pursue. Some sources state mixture model to be a good fit would this be the case?
Much Appreciated,
Lucas Clapp
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It is better to approach Eularian-Lagrangian Model in this regard. Most of the comparative research articles shows better fit with this model than any other models.
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In air-water multiphase flow CFD simulation's it is common to use a VOF = 0.5 to track or identify the position of interface or free surface. I would like to know why this criteria is used and if it can always be assumed the same. Otherwise, I would like to know if volume fraction can be taken different to 0.5 and, if so, ask them about a methodology to find this volume fraction.
Below I describe a case that I am simulating in Ansys Fluent:
-Sewer pipe with Length L=6 m (aligned with the x axis), Diameter D=200 mm (8 in) and longitudinal slope So = 0.005 m/m.
-Simulation in steady state of sewer pipe considering biphasic flow air-water flow.
-Model Volume of Fluid (VOF) with implicit formulation and Open Channel's submodel.
-Boundary conditions: Inlet as mass flow rate = 26.51 kg / s; outlet = Pressure outlet. The mass flow entered is such that the ratio y / d = 0.61 (that is, occupation of 61%).
-Turbulence model: k-epsilon RNG with Enhanced Wall Treatment function (y + <5).
-Pressure-Velocity Coupling method: Coupled + Pseudotransient solver.
-Spatial discretization: Least Squared Cell Based; PRESTO!; Momentum, k and epsilon with 2nd order schemes; Volume Fraction = Compressive.
-Run Calculation: Time Step Method = Automatic with Length Scale Method = User-Specified; Length Scale = 0.064 (Hydraulic Radius); Time Scale Factor = 0.3.
To verify convergence I did the following:
* Residuals at 10-4 for all variables.
* Mass balance between input and output.
* Pressure drop between inlet and outlet.
* Velocity at Inlet and Outlet.
* VOF fraction for various orthogonal planes to the pipe at x = 0.5m, 1.0m, 1.5m, 2.0m, ..., 5.5m. I configured them as Surface report-Area Weighted Average, for the Field Variable=Volume fraction and Phase=water.
Convergence is good in terms of residuals, mass flow rate (1x10-6), drop pressure, velocity. In VOF monitors the trend also stabilizes towards values between 0.40 and 0.75.
I know a flow profile along the pipe. In my initial simulation with refined mesh, with elements of 0.02mx0.005mx0.003m, [this is (dx) (dy) (dz)], I noticed that the theoretical profile is closer when I choose VOF = 0.7 and not VOF = 0.5 as is usual in the practice.
From the above my doubt arises about the VOF fraction to choose.
Thanks!
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Leonardo Henao; Use the HRIC Scheme and refine the mesh in the z-direction (the wave elevation direction).
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Hello everyone;
I m trying to model the mixing of two miscible liquids inside a circular tank by using Ansys-fluent and i m confused which model of multiphase flow i have to use to model such case (VOF-Mixture or Eulerian).
Best regards and thanks.
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I think that the "species transport model" is the most suitable for your simulations, it's more suitable for the mixing of miscible fluids but you must be careful because you need to disable the reaction process.
For the colleagues who recommended the VOF model, I inform them that it is suitable for multiphase flows where fluids are immiscible, and for the others like mixture and Eulerian models the problem arises that you can't introduce the diffusivity coefficient particularly to validate with previous work.
Good luck.
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I am currently studying about non isothermal multiphase flows and I want to model with non isothermal lattice Boltzmann methods. Any relevant input is always welcomed. Thank you!
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A good starting point is the book of Krüger et al. as well as the open source code OpenLB and the LBM spring school, see www.openlb.net .
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I am trying to simulate pyrolysis of biomass in different reactors and I have been using multiphase flow capabilities on top of conjugate heat transfer, species transport and laminar flow. I want to know more about the steps in Fluent to include multiple reaction pathways and being able to include more complicated kinetics in the simulation.
Thanks in advanced!
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Thank you very much Swapnil! I
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We are doing RTD study (pulse input method) for the flow through a packed bed in case of single phase (water) as well as air-water multiphase flow. We are facing problem about the experimental result of the Peclet number calculation, sometimes it increases with increasing velocity of the phases and sometimes it decreases. Now, my question is what would be the actual trend of Peclet number when the velocity of water increases for single phase flow and when the velocity of air increases (water inlet velocity fixed) for the multiphase flow? Please help me with the answer if you have any idea about the problem.
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Please mention the direction of motion of both phases i.e., water and air and tracer inlet position.
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Hello all,
I am trying to study a very simple case of bubble rise ( air in water) using Phase field method in COMSOL. However, again and again I get this error " fFailed to find consistent initial values.
Last time step is not converged."
I see that there is some scaling setting that needs to be done. However, just to see of things work well, I took the exact parameters as given in example of capillary filling.
The only difference in my case is that I try to study the rise of bubble instead of capillary filling.
While the given example worked well, changing the boundary conditions and physics lead to an error mentioned above.
May some one help in this regard, please? How to deal with this issue. I looked across but not much was found.
Thanks
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Hi, I was able to to it. Thanks for your reply. It was really helpful.
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What's the meaning of the capillary entry pressure (Pd or Pe) in Brooks Corey model giving the capillary pressure as function of a fluid saturation Pc=Pd*S^(-1/lambda) and how it can be determined for a binary immiscible flow in porous media?
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You also need to consider contact angle; so the corrected version is as follows based on Franken's model:
Pe = -2*B*sigma*cos (theta)/ R_max
where B depends on the pore geometry shape: 1 for cylindrical pores and 0<B<1 for non-cylindrical ones. Note that for B =1, the equation converts to well-known Young-Laplace equation.
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I got one really good paper on "Two phase modelling in ANSYS FLUENT", in which they have used UDF and linked them to Governing differential equations of VOF Model in ANSYS FLUENT. The Paper I have attached below, in which terms to be added as source term is also given.
I am going through UDF manual of ANSYS FLUENT and all the materials that I have with me for understanding how to link the source terms though UDF with the Governing differential equation of VOF model.
If you have any program written in C for adding the source term to governing differential equation of VOF model, please share your inputs on this topic
Thanks regards,
Somnath Rangrej
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Please write your considering sources as formulas here. Maybe I could help.
Thank you.
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Dear all,
I am modelling a drying process using a Eulerian multiphase flow in Fluent. The rate of evaporation of water-liquid is changing depending on the volume fraction of water liquid in the porous media. Therefore, to calculate the mass transfer I should write a udf which calculate the mass transfer according to the volume fraction which is provided in each time step. When searching in udf guide, I face C_VOF for this but it is mentioned that this can be used to get volume fraction in VOF multiphase model. I will really appreciate if anyone help me how i can get the volume fraction in each timestep in Eulerian model.
Thank you in advance,
Elham
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You can also use the C_VOF. It works for both models.
For example, you can just simply write: v1=C_VOF(cell,liq1);
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I am currently doing a gas-liquid phase change simulation, but the false phase change near the gas-liquid interface occurs due to the spurious velocity. Is there any way to reduce or eliminate this non-physical phenomenon?
Thanks for your help
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Thanks for your answer very much. I have no plans to use the Shan Chen model although it can simulate this issue with good results. I also noted that there are several related works, such as [Taehun Lee, Physical Review E 2006, Journal of Computational Physics 2016] , that can eliminate the parasitic currents. However, I still want to know about some other technologies that can be employed on non-uniform meshes. Can you recommend some related literatures?
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We all know that VOF method in multiphase flow is conservative...
when using this with method in free surface or interfacial flow we ended with mass loss even with a a finest grid, is there any way to conserve the overall mass of liquid ?
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Okay I made a systematic study recently with OpenFOAM about the issue that you were talking about. And it seems not surprisingly, you will over all lose mass/vol. while you track the whole mass in the system. And the reason for this is that the equation which is solved for the interface (alpha advection) is of hyperbolic type and once you try to solve it with a dissipative discritization (Upwinding) it'll make minor errors in your alpha field resulting in overall misbalance of mass/vol. in your enclosed medium. Of course this is not noticed once you try to simulate an open case. Anyways, what is important is that you cannot avoid this dissipation in the solution of alpha because it has also a good side and that is "stabilization". The good news is refining the cells at the interface would make this effect less vibrant.
BTW check the implementation of VOF in OF as well (interFoam solver) regarding the interface compression...
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Dear Fellow colleagues,
I'm trying to simulate a metallic powder flow under the effects of gravity only in a circular tube in 2D. I'm using the eulerian multiphase model, fluent doesn't seem to like that the density of the secondary phase (the powder phase which is 5500 kg/m3) is higher than the density of the primarty phase (air), up to 5-8 kg/m3, there's no divergence but higher than that, the divergence starts from the early iterations!
Any advices on how to solve that?
Thank you in advance
Karim ZAYNI
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Volodimir Brazhenko
Sorry for the late reply, I didn't receive a notification for your last reply for some reason.
How can I set a pressure drop exactly?
Gravity is on.
For the geometry, it's a 2D rectangular tube 20 mm long and 0.7 mm wide placed vertically, I patched the whole tube with powder.
DPM is working fine but the eulerian granular model is more interesting for me.
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If so, why are they defined as "suspensions" in the majority of literature, including high-ranked journals?
Although both are heterogeneous two-phase systems, as far as I know, in suspensions, particles settle on standing. While in colloids, the solid phase remains dispersed and does not separate on standing.
I am no expert, but this truly confuses me. Am I missing something?
Your feedback is appreciated!
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Yes Ofcourse
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how to add a wall flux boundary condition of the primary species onlu?
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I would have a look at the newly introduced expression language capabilities in ANSYS Fluent 2019 R1 and R2. I could imagine, that using expressions, you do not have to write a UDF anymore? In an expression, the defined wall flux could be just multiplied with an expression value, which is always 1 for the primary phase of your multiphase flow and always zero for all other phases. I have not yet tried this by myself in ANSYS Fluent, since usage of expressions in this solver is rather new, but that is how I would implement it in e.g. ANSYS CFX using CCL language. New expressions in ANSYS Fluent should allow to do that at some point as well.
Regards,
Dr. Th. Frank.
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I am using Fluent for simulating multiphase flow (gas-liquid) inside micro channels (0.1-16 microns). I have a problem in making water (as wetting fluid/hydrophilic) flowing as a film on the insid the wall of the channel. Please could anyone help with this one?
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I would suggest trying to define wall slip in the wall boundary condition and see where that leads you.
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I have simulated a multiphase flow in Ansys fluent and now want to transfer the pressure load from the fluent to the ansys mechanical to do a fluid structure interaction.
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Simply plug and play the (ijes) or parasolid model into the ansys workbanch and then try to resolve it
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If so, how can we define the Knudsen number for solid nanoparticles dispersed in a liquid carrier? And how can the mean free path of liquid molecules be calculated?
Conventionally, Knudesn number is used in the framework of the kinetic theory of gases to judge the levels of gas rarefaction and slip-boundary effects. Is the same concept somehow applicable to particulate flows (such as nanofluid flows) with a liquid carrier phase?
Please note that in my approach, the particle phase is already treated from a discrete perspective and only the fluid phase is treated as a continuum. Therefore, my purpose is to judge if this treatment of the fluid phase is correct.
Also please note that I am aware of the popular use in the nanofluid literature of a Kundsen number defined as MFP/D, where MFP if the mean free path of the liquid molecules (?) and D is the nanoparticle diameter. However, I am not sure about the applicability of this criterion for treating the fluid phase as a continuum in a particulate flow system.
Your feedback is much appreciated.
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The Knudsen number is defined via the mean free path l_fp. In liquids the mean free path hardly can be introduced. Though liquids differ greatly from the solids, the marked molecule in liquid actually is moving under the impact of the self-consistent-field caused by the other molecules. Introducing the concept of the quasi-particles we can introduce the mean free path for those quasi-particles. The last is of the order of the mean distance between the molecules. Knudsen number as Kn_p=l_fp/D, where D is the nanoparticle diameter formally can be introduced, but how can it be used for the continuous model justification? The Knudsen number arises as a dimensionless parameter in the kinetic equation. Small Knudsen numbers correspond to the continuous model, even taking into account, that for the dense gas, all the more for the liquids, much more complicated kinetic equation compared to the Boltzmann equation should be used. That parameter has no practical use without considering of any type of the kinetic equation. For the nanoparticles Kn_p may not be small, so I see no application field for such parameter, specially taking into consideration the long-range interaction of the particles via the liquid.
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maybe the small amount of the DataSource
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Hi Weijia Lu,
Great point. Machine learning uses algorithms to parse data, learn from that data, and make informed decisions based on what it has learned. Deep learning structures algorithms in layers to create an “artificial neural network” that can learn and make intelligent decisions on its own.
Best,
Moh.
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How can we calculate capillary pressure in multiphase flow system in a porous reservoir with relative permeability and saturation as the given values. What I require is data on capillary pressure with change in relative permeability of gas or water saturation. This is in context of CO2 sequestration in deep saline aquifers.
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Well,
q=kA (P1- P2)/ µL---------------------- (Equation ) where
q = Volume flow rate
k = Permeability
A = Core area perpendicular to flow direction
P1 = Upstream pressure at location 1
P2 = Downstream pressure at location 2
µ = Dynamic viscosity of flowing fluid
L = Distance over which pressure drop (P1- P2) occurs.
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What are the differences between capillary pressure and interfacial tension in the context of multiphase flow in porous media? I understand that capillary pressure is the pressure at the interface between two phases in contact. Then what precisely is the interfacial tension?
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Hi Ankita
Interfacial tension is the work (J or N.m) that is required to increase the surface area of an interface between two phases, expressed per unit surface area (m2). The units of interfacial tension is therefore J/m2, or N/m.
Given two immiscible liquids in a thin tube, capillary pressure is the difference in pressure accross the boundary between the two phases. It results from the interfacial tension between the two phases.
All the best
Johan
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Hi
I am simulating a kind of electrolyzer in Fluent. Consider a 2D-box, the bottom boundary is opening, top boundary is degassing, gas is generated from a part of left side boundary and right boundary is wall. I did the mesh dependency test and got dy=1mm is an optimum size. Now, if I set the vertical size of cells close to the degassing boundary equal to 1mm the total amount of gas in the domain will be A%. But, if I change the cell size close to the degassing boundary to a smaller value (e.g. dy= 0.5mm) then the total amount of gas in the domain in the steady-state condition will change. Note that I only change the cell size close to the degassing boundary to see the effect of cell size of the performance of the degassing boundary.
I know that Fluent specifies a mass sink for the gas phase in the cells adjacent to the degassing outlet which is related to the cell size (i.e. mass sink=integral (e_g * rho_g* u_n*dA) ), but I do not know how I can get similar results with degassing boundary when changing the cell size. any idea?
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Thanks a lot Ricardo
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I need to compare results for a simulation with nanofluids in a coiled tube using the single-phase and two-phase methods in FLUENT. The single-phase method works perfectly well. However, I am confused with the development of the two-phase Mixture model. The pertinent literature states that the fluid properties need to be defined through the use of the effective properties (as in the single-phase simulations). Hence, I am not sure on how to define the model in FLUENT. 
Therefore, if we define the mixture with two phases, my understanding is that the base fluid properties (water) will be defined with the UDFs for the effective nanofluid properties. Then how can we define the properties of the nanoparticles i.e. the second phase? 
Am I right to assume that for the second phase, the granular option needs to be activated?  
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Its calculated based on effective mixture properties.
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Hello all
I am simulating hydrogen generation in an electrolyzer compartment using Eulerian model in Fluent. The final amount of gas in the domain when the solution reaches steady-state condition is about 25% and 14% for Explicit and implicit solvers respectively. What is the reason for this difference? I have checked even very small values for the time-interval to see if two solutions become similar, but they did not. Any idea about the reason for this difference between the results? How can I get similar results?
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I think you should check mesh independency for your solution, changing the solver, will result in change in the mesh dependency criteria.
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The multi-phase fluids are widely used for annular hole cleaning, but I am not sure what advantages do they offer compared to single-phase fluids in overall removal of cuttings for the annulus.
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hi
used for non Newtonian flow
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How can we model multiphase flow of DEM (discrete element modelling) and SPH (smooth particle hydrodynamics)/ lattice boltzman method using comsol. Also if there is any other good software to perform similar problem
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You can check below mentioned article:
Article A LBM-DEM solver for fast discrete particle simulation of pa...
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I am analyzing the copper water nano fluids  in fluent by multi phase  Eulerian-Eulerian approach.i want to describe the material properties of copper nano paricle which are dispersed in water.i was able to describe the water which is primary phase.i want to specify the copper nano particle as secondary phase so how can i describe the secondary phase material properties as a fluid since copper nano particle is a solid how will i convert the properties for solid to liquid
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Hi Saptarshi,
Granular Viscosity in a Eulerian-Eulerian mixture model indicates the sum of kinetic, collisional and frictional viscosity components for the solid particles.
In general, kinetic viscosity is calculated using an expression given by Syamlal et.al from [1] or Gidaspow et. al [2] depending upon the particle volume fraction and particle diameter used.
Collisional viscosity is modelling by an expression given by Gidaspow et.al [2]
Frictional viscosity is calculated by an expression given by D.G.Schaeffer [3]. This frictional velocity is significant only when the volume fraction is closer to the packing limit (63%). In nanofluids, we generally consider a volume fraction less than 5% due to practical constraints. Hence, frictional viscosity component is generally ignored for nanofluids.
Solid pressure indicates the pressure gradient term in the fluid-solid momentum equation. It is generally estimated by a model proosed by Lun et. al [4]
In order understand more about these concepts, you can read on kinetic theory of granular flow.
[1] M. Syamlal, W. Rogers and T. J. O’Brien. MFIX Documentation: Volume1, Theory Guide>. National Technical Information Service, Springfield, VA. DOE/METC-9411004, NTIS/DE9400087, 1993.
[2] D. Gidaspow, R. Bezburuah, and J. Ding. "Hydrodynamics of Circulating Fluidized Beds, Kinetic Theory Approach". In Fluidization VII, Proceedings of the 7th Engineering Foundation Conference on Fluidization. 75–82. 1992.
[3] D. G. Schaeffer. "Instability in the Evolution Equations Describing Incompressible Granular Flow". J. Diff. Eq. 66. 19–50. 1987.
[4] C. K. K. Lun, S. B. Savage, D. J. Jeffrey, and N. Chepurniy. "Kinetic Theories for Granular Flow: Inelastic Particles in Couette Flow and Slightly Inelastic Particles in a General Flow Field". J. Fluid Mech. 140. 223–256. 1984.
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Hello everyone,
I want to simulate a multiphase - flow (eulerian - eulerian) through a porous media in Ansys Fluent without the effect of diameter. In the eulerian model, by default only drag is active for the phase interaction between the two phases. So the effect of diameter should no more be present, if I disable drag. If I disable drag (from schiller-naumann to none), my simulation gets unstable and I get the message "floating point exception". Can anyone help what I can do, or give me an alternative to delete the effect of diameter in my simulation?
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Tristan Davenne is entirely right. Essentially what you mentioned about your current solution points in the same direction. It seems to me, like ANSYS support has recommended to you to switch from a disperse multiphase flow formuölation to a VOF-like (VOF = volume-of-fluid) formulation. VOF exists in the ANSYS software in two flavours - homogeneous and inhomogeneous. The homogeneous model with just 1 set of momentum equations follows the assumption, that both phases move with the same velocity field. In that case no assumptions or knowledge about interfacial momentum transfer is needed. ANSYS has implemented an inhomogeneous VOF model as well. In that case from the local ratio in volume fractions of both phases an inherent drag term is deduced, but in that case you don not have to specify it yourself. It assumes, that separatign interfaces between the two phases are rather macroscopic and resolved by the simulation like typically done in free surface flows.
Regards,
Thomas Frank.
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Dear All,
Greetings.
I would appreciate it if anyone can recommend a book (or any other related reference) for miscible multiphase displacement flow especially if it is for Non-Newtonian fluids in Oil well cementation.
Thanks in advance.
Best Regards.
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Dear Professor Suresh,
Thank you for your reply.
Much appreciated.
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I have a thin porous material whose saturation needs to be determined. The relative permeability for a multi-phase flow is to be determined through the porous material and in order to express relative permeability as a function of saturation, I need to determine the saturation. The sample is of the dimension of 10mmX5mm and thickness of approximately 500 microns. How can I effectively measure the water saturation. Also, I think the internal methods of saturation determination like X-Ray method, neutron scattering would be not very effective considering the small dimensions of the sample. Correct me if I'm wrong.
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If I understand correctly, it is an elongated tube that can serve as a waveguide. The electromagnetic waves can not penetrate the wall of the pipe, even at very high power. You have to couple the energy on one side of the wet diaphragm and measure the electromagnetic energy on the other side with a similar probe. Suitable coupling elements can be found here:
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In a case where there is a multiphase flow through a heating pipe (heat flux is provided), if I use (say 0.3kg/s) mass flow rate as tube inlet boundary condition at a known temperature, can I use same mass flow rate (0.3kg/s) as tube outlet boundary condition?
Or will there be change in mass flow rate at outlet.
Actually, I need the BC at outlet to be like 'Outflow' (as we use it in Fluent). I don't know the property of fluids at outlet. Rather, it is what which is to be find out (like temperature, vol. fraction, etc.).
Also, how can I allow backflow (if needed) around outlet?
In 'Opening' type BC, I do not understand how I can specify Opening Pressure and Temperature if they are yet to be calculated by the solver?
Thank You.
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What would you say about the 'Bulk mass flow rate' available for Outlet boundary condition.
For that, no volume fraction information is asked in CFX-Pre.
Should I conclude that, if I use that option: the liquid+vapor=bulk; it would mean that it is necessarily kept constant (0.3kg/s both for inlet and outlet)?
If so, is it Physically possible as well?
P.S.: my fluids are liquid water and water vapor (wall boiling case).
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Hi guys,
I recently ran into a paper simulating pore-scale porous media with FVM-VOF model and then validated it with another numerical approach based on LBM named Shan-Chen LBM model and received more or less the same results; however, it did not mention anything about the pros and cons of these two approaches except that LBM is more flexible in dealing with complex geometries and boundary conditions than traditional FVM-VOF.
Has anyone got any clear idea and explanation of the difference between these two approaches, e.g, computational time or accuracy in capturing interface, etc?
Any helps or comments would be appreciated in advance
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Dear Sir,
For multiphase flow inside porous media, you can use the mathematical formulation of TPMM along FVM instead of VOF. For further information, please see my articles in my page and also you can contact with me at any time.
best regards
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Why does the imbibition process need a much higher pressure than the drainage process in the two-phase fluid flow in porous media?
Principally, because capillary pressure plays a positive role to drive the flow of wetting phase (e.g., water), the flow in an imbibition process (e.g., water displacing oil) should be easier (less pressure cost) than in a drainage (e.g., oil displacing water) process.
However, as shown by many laboratory core-scale test results, an imbibition usually needs a much higher pressure (e.g., 100 kPa) to drive the flow than a drainage (e.g., 20 kPa) under the same injection rate (e.g., 0.5 mL/min).
The high pressure during imbibition should be not due to the viscosity difference between fluids. When injecting either one of the phases alone in the media, the pressure drop is quite low.
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I fully agree with previous answers. But your question is not clear enough.
the distribution of fluids (previous history) and wettability (if the viscosities are similiar) are the controlling factors for the pressure needed to flow. involving capillary pressure muddles the issue.
For example, if your water saturation is 40 % and all the other variables are the same. Not all the pores have 40%! some will have 100% and others 20%. Therefore, the pressure drop will be different for different pore size distributions, mainly if they are not unimodal.
Also, during imbibition and drainage at the same saturation you will have different fluid distributions and as a consequence different pressures.
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Hallo fellow Researchers,
I need to update my knowledge on Multiphase Flows and Fluidization processes. Especially with Continuum and Kinetic Theory Descriptions.
Does anyone know if something changed about understanding the Continuum and Kinetics during last 20 years?
Are there some newer books with updated data or Gidaspow's work is complete for now?
Thanks in advance and Best Regards,
Stan
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Multiphase Flow: Theory and Applications
by P. Vorobieff, C. A. Brebbia
Publisher: WIT Press / Computational Mechanics (April 18, 2018)
Multiphase Flow Handbook, Second Edition
Efstathios Michaelides, Clayton T. Crowe, John D. Schwarzkopf
September 1, 2016 by CRC Press
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Hello all,
May some one suggest references wherein some relation has been proposed ( and proved ) between grid size and cahn-number.
In my understanding, it is known that one should consider about 3 grid points ( minimum as proposed by Jacqmin) in the interface.
Well then as per that relation, Cn= int_thickness/L ( L being characteristic length of the domain).
Thus, we have Cn= 3*grid_size/L . But is this correct. I read somewhere ( can't remember where) that its best to have grid size varying from Cn-Cn/4.
May some one help in this regard.
Thanks
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Thanks a lot for your kind references.
Deewakar
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What are the recent advancements to dissolve hydrogen in water?
I couldn't find any recent (2014-2015) articles on dissolving hydrogen in water. It would be great if someone could help me in this regard.
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As long as you have low mixing, a sufficiently high water column and volume (to provide buffer against liquid/gas phase contact) and a membrane/module which can inject the gas (smaller pores work better; "pore-free" silicone is also effective), and you can control the gas input pressure/flow, you should be able to inject high amounts before the liquid phase becomes fully saturated and bubbles start to form. The Henry's constant and mass transfer characteristics (which would severely limit the amount of H2 you could inject (i.e. 1.6mg/L) if the liquid phase is open to atmosphere) are then not limiting in this case. In a similar vein, if you have high H2 partial pressures in the gas phase and your reactor is well-sealed, you can dissolve more as well.
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I am modeling multiphase flow and i counter this error: In Analysis 'Flow Analysis 1' - Domain 'fluid': The following materials require Viscosity to be defined: 'Aluminium'
i try to use alminium as my dispresd solid phase and water as my countinus phase. How can i solve this error?
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Currently, the fluid drop impact on solid walls is an important research area in the scientific community. The droplet spreads out on the wall after impact. In some cases, the tip of the spreading lamella levitates and travels along the surface without touching the wall. Quite interestingly, this is observed in drop impact on both hydrophobic and hydrophilic surfaces. What are the main reasons for this phenomena? How can we categorize them?
The image is from
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Following!
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I am trying to simulate the gap resonance between two floating bodies and with a gap of 3m under the effects of ocean wave (direction longitudinal of the ships body) . I am trying to put surge, sway and yaw as fixed. There should be a damping effect on floating bodies due to viscous effect and radiation . How do I determine the linear and damping coefficient of such bodies. This is my first time simulating a multiphase flow and needed advice on this.
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You shoud add function ovject to your controlDict in order to read forces etc.
From the forces probably you can calc what u need.
Franco
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As in multiphase flow it is said that surface tension plays a role in mini channels rather than gravity, I am unable to understand, is there any mathematical equation that supports or experimental study?
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Hi
You can simply understand it by " Surface area to volume ratio" (SAV) concept. From dimensional analysis, SAV=1/L. so when a channel characteristic length is 1mm, SAV=1000 , that is surface effect are 1000 times higher than volume effect. Gravity is a body force which acts on the volume so its effect compare to lets say friction is 1/1000 smaller in a minichannel with characteristic length 1 mm. For heat transfer surface area is important so mini or microchannels are better heat exchangers.
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Some thermodynamics confusion.
Assume ideal gases for simplicity.
Are kinetic energy (K) and internal energy (U) for gases, different from one another? As I understand,
dU = n Cv dt
And if some work is done by a gas adiabatically, then
heat change dQ = 0
Now we can have two cases:
1) Expansion occurs at the cost of internal energy of the gas and so gas temperature falls as the gas expands. So, U decreases.
Or,
2) As the temperature falls, the velocity of the gas molecules deceases too which then consecutively lowers the K of the gas.
So, are K and U the same physical quantity? Do they imply the same physical parameter of a system or something different? Or, may be both K and U undergo change in such a process?
Another issue is if work (classically) done = P V
then dW = P dV is seen more often. I am aware that W is not an exact differential, still shouldn't it be dW = P dV + V dP, as one can intuitively guess that during an adiabatic expansion of a gas, as volume increases, pressure will change (fall?) too? Why V dP is often left out?
Any comment will be appreciated.
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Dear Mr. Pandey,
let me try to help you out and clarify your doubts in a simple way.
A gas is constituted by many many molecules, each one having its own velocity. However, while studying a gas flowing in a given domain, we cannot follow each molecule so we introduce the concept of particle.
A particle is constituted by a bunch of many molecules (say millions) in the neighbourhood of a point, which however has dimensions much less than the domain to be studied. So the studied domain is composed of a very large number of particles. This is called the continuum assumption which is not valid, e.g. in rarefied flows.
More precisely, the particle must have a volume that is much larger than the cube of the gas mean free path and this volume must be much smaller than the volume of the studied domain. For air at STP, a cube having its side equal to a mean free path contains about 10,000 molecules.
The velocity of a particle of a single component gas is generally defined as the vectorial average of the several molecules contained in it. Of course, in a multi-component gas, a weighted vectorial average has to be performed. So, the velocity of a particle can be regarded as the velocity of the center of mass of the particle itself. Besides, the velocity of a particle depends on the adopted reference frame.
The kinetic energy of a gas particle is the one which is evaluated with the velocity of said particle.
But we have to remember that each molecule has its own velocity so, we may define the peculiar velocity of a molecule as its actual velocity minus the velocity of the particle it belongs to. The peculiar velocity of a molecule does not depend on the adopted reference frame because it is always measured with respect to the center of mass of the particle.
In this simple model, the internal energy of the particle is represented by the average kinetic energy of all the molecules contained in the particle evaluated with the peculiar velocities.
It is like if we split the total kinetic energy of the molecules in two parts, a macroscopic one (the particle kinetic energy) and a microscopic one (the particle internal energy).
Going to your example, in the gas expansion, the particle velocity increases ond so does the kinetic energy, while the internal energy (and so the gas temperature) decreases.
I hope to have been clear enough even not using equations.
Best regards and good luck for your work
Carlomagno
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I am working on a multiphase flow through a porous medium. in my system I am introducing water at a constant flow rate in a porous medium filled with oil. There is outflow only when pressure in the system has exceeded 400 psi. please help me in how to put this condition in gambit.
Thanks.
Regards,
Shilpa Nandwani
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Are you having back flow issue in defining the outlet pressure in FLUENT? You have to be selective in inlet velocity also to avoid the back flow.
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which is better for temp measurement of fluid flowing inside tube in upward direction. there are an options by use thermocouples or PT100, which way is more acceptable for such case? I hope to hear from you if any one have an experience. for information the flow is multiphase flow.
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Dear Mohammed,
I'a agree with James Garry. In my thesis preparation, i tested the position of temperature sensor in cylidrical tube. The accuracy of results depends on the position of the sensor and the flow regime which must have a high Reynolds number value.
I f you need more details about this, i'am ready to help you.
With my best regards!
Dr. Adel OUESLATI
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Dear all,
I am using multiphaseInterFoam for one of my case setup. I have generated 3D mesh using fluent and then convert it into openFOAM format.
Quality of Mesh seems to be ok. Check mesh result is as below.
Checking geometry... Overall domain bounding box (-3.65028 0 -3.91767e-016) (6.37721 4.4 3.6496) Mesh has 3 geometric (non-empty/wedge) directions (1 1 1) Mesh has 3 solution (non-empty) directions (1 1 1) Boundary openness (-3.1831e-017 1.41703e-015 8.34435e-017) OK. Max cell openness = 3.08743e-016 OK. Max aspect ratio = 8.96002 OK. Minimum face area = 4.24312e-007. Maximum face area = 0.108377. Face area magnitudes OK. Min volume = 1.50115e-010. Max volume = 0.0121032. Total volume = 90.7938. Cell volumes OK. Mesh non-orthogonality Max: 68.5635 average: 17.1285 Non-orthogonality check OK. Face pyramids OK. Max skewness = 0.983603 OK. Coupled point location match (average 0) OK.
Mesh OK.
When I run this simulation in Fluent it works but in case of OpenFOAM it diverges due to values of k and epsilon only. For initialization of k and epsilon, i have calculated their values using standard formulas at the inlet and at outlet zeroGradient condition is used.
With the same mesh and case setup, if I run for laminar case in OpenFOAM then it works.
Moreover, default convergence criteria for k and epsilon in Fluent is 10^-3 while in case of OpenFOAM, it is 10^-8 (tolerance in fvSolution). I have also try to alter it but it does not work and solution getting diverges after some iteration.
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Dear Sagar,
I would recommend that you, for the time being, fix the convergence criteria for both k and ε to 1e-03 in OpenFOAM and try achieving "initial convergence" using these values. I am worried about the values of k and ε that you are considering at the inlet as well as during initialization.
The major difference between transport equations for momentum and k and ε is that production/extinction of both k and ε is possible in the domain; ε acts as a sink for k whilst ε2/k acts as a sink for ε (termed as the dissipation of dissipation).
You can understand the couplings between k and ε transport equations using this link:
If you observe those equations carefully, you will notice that both k and ε are "produced" in regions of large strain Eij. However, whilst the production term for k is 0.18*(ρk2/ε)*EijEij, the one for ε is 0.26*(ρk)*EijEij (I replaced turbulent viscosity, μt and model constants Cμ, C into the production terms). Observe that there is an "additional" multiplier of k/ε in the production of k. Hence, at the beginning of the simulation, if k/ε>>1 (the initialized field is NOT dissipative), then it can be expected that k will grow more rapidly in the domain compared to it's sink term ε. This would result in excessive production of k (which is a problem that is commonly encountered in SKE based simulations). Whilst large k in the domain itself is unphysical, what would be even more unphysical is a very large turbulent viscosity μt being generated as a result of k/ε>>1.
In order to debug the solution, analyze spatial distribution of values of k and ε and also how they grow as physical time progresses in the simulation. If you observe that k>>ε try initializing the solution from μt = μ which assumes that turbulent viscosity is very low at the beginning of the simulation (which, atleast according to me, is a reasonable assumption) and is in fact of the same order as fluid viscosity μ.
However, if you are able to achieve convergence in FLUENT but not in OpenFOAM, you may need to read more literature regarding numerical treatment of SKE in OpenFOAM. Also, if I am not wrong, maximum allowable limit for μt / μ (turbulent viscosity ratio) is 1e+05 in FLUENT. Is this limit lower in OpenFOAM?
One last advice: Kindly share more details of your simulation setup (problem description, physics involved etc.) so that your question attracts more relevant researchers on RG. :) :)
Hope this information helps you in debugging your simulation.
Best regards.
Shaswat
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Hi,
I work in the area of multiphase modeling and encountered the following problem.
I want to use weno algorithm on the projected characteristic variables of the problem, as follows
W(i)=inverse(P(i+1/2)) V(i)
The estimation of P is done via arithmetic average or roe's averaging of V(i) and V(i+1) where V is the primitive vector, W is the characteristic vector and P is the diagonalization matrix of the corresponding jacobian matrix of the system.
However, the cell value of the characteristic have the following structure: the same value for all the cells except on cell which has a different value. This structure of the data is obtained for the shock tube problem (and some other problems as well). If I try to implement weno on this kind of data pattern, eventually spurious oscillation would be emerged.
Summarizing s the problem: W(i)=1 for all “i” except for one cell which has value other than one.
For the one-phase problem, the data pattern of the characteristic values is different and therefore this problem does not exist. Trying implementing weno on conservative or primitive variables, results in oscillations as well
Is it possible to circumvent this problem somehow? should I think of other ways to obtain high order spacial accuracy without weno knowing this data structure of characteristic variavles?
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Dear Sir:
a) SIMPLE algorithm is used more for steady-state problem
b) PISO algorithm is more for unsteady analysis, depend of  your investigations, that is the case of unsteady partial cavitation problems.
good luck
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Disclaimer - this is my 2nd ever Ansys-Fluent simulation and I have not had any formal CFD training yet.
I am working on a simple ANSYS Fluent (16.2) multiphase flow simulation .  The geometry is a larger straight tube with a smaller straight tube inside the larger one along the same axis with one end of each tube sharing the same plane.  
 I intend on having the the ring around the smaller tube defined as an inlet for one fluid type (Fluid 1) and the smaller tube an inlet for a 2nd fluid (Fluid 2) with the mixture coming out the far end. See attached model rendering.
I am at the point where I need to configure the Multiphase Model in Fluent and I am having difficulty identifying the correct model and parameters for the type of mixing model I hope to create.  Fluid 1 will be a glycerol like fluid with a pulsatile flow up to 50cm/sec, and Fluid 2 will be a constant flow (or pulsatile flow) up to ~140 cm/sec of a homgeneous solution of specified concentration of an additive with a more syrup like viscosity.  I am hoping to use the simulation to understand how Fluid 1 dilutes Fluid 2 farther down the pipe and how the net concentration varies over distance with the pulsatile mixing. 
It appears from my searching I should use an Eulerian Multphase model based on page 8 of http://www.bakker.org/dartmouth06/engs150/14-multi.pdf and https://www.sharcnet.ca/Software/Fluent6/html/ug/node876.htm .
I can rule out enabling the boiling model and evaporation-condensation parameter options but I am unsure of whether to use Multi-Fluid VOF Model or Dense Discrete Phase Model  in the Eulerian Parameters config window & If I do pick Multi-Fluid VOF how do I determine what to specify for the volume fraction cutoff and Courant Number?
Thanks in advance for any advice.
Erick
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Hello Erick,
Can you provide some more information about the fluid properties of the two phases? Do you have any experimental data that you can use for validation of the simulations? As far as I understand your setup, it might be possible, and sufficient, to use a species transport model which is much less computational intensive than a two-phase model. The Eulerian MP models are typically used when high momentum exchange between the phases occurs, e.g. due to drag, particle-particle interaction, surface tension, etc. and when the phases are in different physical states (gas-liquid, gas-solids, liquid-solids etc.) are present in the system. However, if you don't have significant droplet formation or stratification in your flow, for example, the assumption of one continuous phase might be feasible. Using the species transport model, you still could calculate the different concentrations as a function of the pipe length and the pulsation.
In particular the VOF models assume a distinct interface between the phases, which is probably not the case when mixing two fluids, even if their density and viscosity is significantly different.
Anyways, if you still want to use the Euler MP model I recommend to leave the default VOF cutoff (further explanation is given here https://www.sharcnet.ca/Software/Ansys/16.2.3/en-us/help/flu_ug/flu_ug_vof_formulation.html). The Courant number depends on the flow velocity, the mesh size and the time step size (see https://en.wikipedia.org/wiki/Courant%E2%80%93Friedrichs%E2%80%93Lewy_condition), but mostly you can leave the default value, too.
Hope this helps for now.
Best regards,
Stephan
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Hello everyone 
I am currently working on gas bubble flow in liquid where i need to find the distance of the bulk phase centroid from the interface using Piecewise linear interface calculation using UDF .
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yeah exactly , I was mentioning the distance of the gas phase center of mass from interface in PLIC calculations .
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Hi,
I am trying to find an empirical formula/graph/simple calculation that I can use to predict the flow pattern inside a horizontal rotating hollow cylinder. I intend to find a method by which I can understand the onset of different flow patters (i.e. annular, rimming, pool .etc) by varying the liquid fill percentage and/or the rotational velocity of the cylinder. I want to find out such data for a variety of setups and hence am not using CFD or experimentation.
It would be of great help if anyone could suggest a source to find the same.
Regards,
Vinayak Krishnan
MSc. Mech. TU Delft
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You don't need to select the moving mesh. Just select the boundary of the cylinder as 'wall' and specify the wall as moving, then select 'rotating', then put the rotating wall in ' rad/sec'.
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Hello,
I am trying to simulate condensation in a horizontal tube on Ansys FLUENT, but every time my simulation diverges. I am still new with this software. Therefore, I took a paper as reference.
My case is as follows: 
> Steady, gravity on, CSF on
> Implicit VOF: Modified HRIC
> Primary phase: Vapor; Secondary: Liquid
> Phase change: Liquid to vapour, as specified in user guide for evaporation-condensation problems.
> Inlet: Velocity inlet, temperature 313.15K
>Outlet: Pressure outlet, backflow temperature 312K, backflow volume fraction: 0.2
> Stationary, no slip wall with temperature 303.15K
I am using the inbuilt Lee model. I have tried decreasing the evaporation-condensation frequencies. When it's too small, it converges but does not condense. When too large, it diverges. In the paper that am taking as reference, the coeff is in the range of 1e6 and 2e7. 
I have decreased my URFs, in vain. My mesh is as specified in the paper, so i think it's not on the mesh... 
Can anyone help or advice me please?
Thank you
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There may be more than one solution offered by nature for your problem given your boundary conditions, fluid properties and initial conditions. You may want to read about the Leidenfrost effect, critical heat flux and "boiling crisis". Your simulation, if physically consistent, may not reach a steady state but enter a limit cycle or diverge from on "stable point" in the state space to another "stable point". It would be correct to use "attractor" instead of "stable point", although one doesn't know until the limit cycle develops. 
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Hello,
I am a part of the San Diego State University's Rocket Project Club. Our club is creating a liquid fueled rocket using the fuels RP1 and LOX. We currently are using an LR101.
We want to conduct a flow test without using flow meters or other transducers. 
This is our idea so far:
1. We set our tank pressures to replicate operational conditions, accounting for chamber pressure.
2. Flow propellant (water) flowing through the injector (and other orifices to account for pressure drops, ie. the coolant jacket) for a set amount of time
3. Carefully capture expelled propellant in a container
4. Weigh the container
5. Voila, your mass flow is pounds of propellant expelled divided by test duration.
6. Have smart people figure out the density/viscosity conversions to an actual propellant (RP1, LOX)
7. rinse and repeat for the other propellant.
How do we do step 6? I have been searching the internet for awhile without much luck. How do we calculate our Cv?
Thanks
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You ought to be able to project the performance of your components by identifying the empirical correction factors for your design calculations. These would be found through your test programme.
Your test programme could be guided by the same principles used to scale wind tunnel models (e.g. Reynolds and Mach numbers). It is understood that you do not have the range of sensors typically available in a test programme, so you'll have to try to project the end effect of all the usual test variables on your result. Again, a thorough understanding of what affects the performance of your system is important. As the designers, you ought to have no problem with that.
Once the appropriate performance coefficients are verified, it ought to be a simple matter of replacing the characteristics of water with those of your propellants in your system =D.
If you're looking for a more detailed breakdown of precisely how to do it, you'll have to share more details about your design and how you went about converging to it.
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Hello,
I am trying to implement the Shepard filter for a system with boundaries defined by Morris ghost particles. The host particles have an associated mass equal to the mass of the SPH particles insuring the no-slip or free slip conditions. 
At the beginnong of the simulation all gas and ghost particles are arranged in a regular lattice.
Is it required to take into account this particles for the Shepard corrrection?
Best regards,
Cristian Achim
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Shepard correction is typically used to improve the density calculation on particles close to free boundaries (well, the consistency of the resulting mass and momentum system is another big story).
The ghost particles, which are used for the simulation of rigid boundaries, provide by default an additional support for the internal, real fluid, particles. Thus, the Shepard correction is redundant for real fluid particles, while I am not sure if there is any good reason to use increased density accuracy for the ghost particles. It is the mass of the ghost particles that real fluid particles "see", not their density.
Regarding the initialization and assuming that you are treating monophase flow, yes, you should give the same mass to all particles.
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Greetings! I'm currently working on Deoiling Hydrocyclone. I selected VOF model to study the separation of oil from water considering both of them to be Eulerien phases. The problem I'm facing is that the results that were obtained show the overflow and underflow volume fraction to be equal to the volume fraction I specified to the inlet (reference and also solution initialization is being done from here). Also the primary phase volume fraction is always 1 near the inlets. please let me know where did I went wrong! Thanks in advance.
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Pradeep, for VOF simulation, Courant number should be < 0.25!
No wonder, the results are weird. Adjust simulation time step size from 10-4 to 10-5 or even lower to ensure this number.
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Kandkukar's formulation may be not a suitable choice. A reference shows It is very different from the experimental value.
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Hoping this helps u.
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I've got a problem about using the macro of TP_COMPONENT_INDEX_I(p,is) when i want to identify the vaporating component in multicomponent DPM particles.In my  case,particle materal is the solution of CO3HNa and bulk gas consists of air and water vapor(So,only water get involved in vaporation).My code to judge vaporation or not listed below.
for (ns = 0; ns < nc; ns++)
{
int gas_index = TP_COMPONENT_INDEX_I(p, ns); /* gas species index of vaporization */
if (gas_index >= 0)
It worked smoothly in fluent,while,no vaporation happened.However,i found the returned value of TP_COMPONENT_INDEX_I(p, ns) is -1.I don't know why the returned value is negative.There are no details about the using of TP_COMPONENT_INDEX_I(p, ns) in fluent udf manual.Can anybody give me some advices?
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@Zoubair Boulahia
I've posted my questions at that website.Thank you
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This is pressure retarded osmosis study. Could anybody tell me , which one should be applicable for the below diagram T3=T4=T9= T10; T3=T4 &T9=T10?
3 to 4: draw solution
9=10 : feed solution
and P3=P4
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this T3=T4&T9=T10 applicable for the below diagram
Pressure retarded osmosis (PRO) was investigated as a viable source of renewable energy. In PRO, water from a low salinity feed solution permeates through a membrane into a pressurized, high salinity draw solution; power is obtained by depressurizing the permeate through a hydroturbine. A PRO model was developed to predict water flux and power density under specific experimental conditions. The model relies on experimental determination of the membrane water permeability coefficient (A), the membrane salt permeability coefficient (B), and the solute resistivity (K). A and B were determined under reverse osmosis conditions, while K was determined under forward osmosis (FO) conditions. The model was tested using experimental results from a bench-scale PRO system. Previous investigations of PRO were unable to verify model predictions due to the lack of suitable membranes and membrane modules. In this investigation, the use of a custom-made laboratory-scale membrane module enabled the collection of experimental PRO data. Results obtained with a flat-sheet cellulose triacetate (CTA) FO membrane and NaCl feed and draw solutions closely matched model predictions. Maximum power densities of 2.7 and 5.1 W/m2 were observed for 35 and 60 g/L NaCl draw solutions, respectively, at 970 kPa of hydraulic pressure. Power density was substantially reduced due to internal concentration polarization in the asymmetric CTA membranes and, to a lesser degree, to salt passage. External concentration polarization was found to exhibit a relatively small effect on reducing the osmotic pressure driving force. Using the predictive PRO model, optimal membrane characteristics and module configuration can be determined in order to design a system specifically tailored for PRO processes.
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We are working on a Plug Flow Reactor carrying a biomass slurry. CFD simulations are carried out in order to simulate and check the possibility of particle settling within the reactor. As the slurry is homogeneous, we are planning to check the system at highest possible density (i.e. of the complete solid cake). This study shows me settling in Plug Flow Reactor. However, in original case, the density varies along with the reaction taking place within the reactor. Is it possible to define the Density as a function of length to get the results much closer to the real time situation?
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In ANSYS CFX, you can define the density of a material within the materials properties section as an expression (defined using CEL). For a case where the density of 1000kg/m3 for x less than 2m and 2000kg/m3 for x greater than 2m, you would use a function:
If(x>2[m],2000[kg m^-3],1000[kg m^-3])
I hope this helps. If not, let me know any follow up questions.
Kind regards,
William 
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UCLA Putterman Research Group fond that:
Sonoluminescence from xenon bubbles in water driven by a sound field with a frequency of 1 MHz. A flash of light is emitted as the implosion reaches 100 nm in size. The spectrum has all colors ranging from far UV to infrared. The sun is a 5,800 K blackbody and this bubbles is more ultraviolet than a 10,000 K blackbody. 
My questions are the following:
1- Is it possible to observe this phenomenon each time when introduced a bubble of Xenon?
2- Is it possible to repeat this experiment several times (tens or hundreds times) for the same water sample?
Best regards
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I am unsure what you mean by several times, during the sonication process there will be many bursts of light. If you are talking about experimentation for a set time period, then turning everything off and starting again then I do not have a direct answer to this question as it depends on several other factors. 
In short, the liquid properties will change. For example, at high frequency there will be an increase in the quasi acoustic streaming that takes place, this in turn can cause agitation at the liquid surface and increase the gas content of the solution. Also what powers would you be using? At higher powers there is an increase in streaming, coalescence and temperature of solution. Whilst gas is lost during sonication, streaming can aid in replacing the gas content. Coalescence can cause degassing and lead to a reduction in the numbers of SL bubbles (although at high frequencies coalescence can be beneficial). The temperature of the solution can have a significant role on the amount of SL taking place, therefore for long sonication times may be an issue. 
Coming back to your original question, In my opinion yes, it is possible. Cavitation cycles can last millions if not billions of cycles, BUT what I'm trying to explain above is that, the amount of light emission will not remain constant and can decrease significantly. The amount of light emission will depend on how the properties of the fluid change over time. 
Why would you want to use the same solution?
It depends on the aims of your experiment, I am unsure what you are trying to do(?)
Just some ideas, hope that helps a little.
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I'm trying to simulate in Fluent a biphase flow of a tank indcued by jets. This system is closed system, so the usual transient approach for localize and simulate the interface by the boundary conditions is not possible. 
I tried to "fill" the tank, using just velocity inlet conditions, calculating the iniciatl interface position by the discharge time, but it didn't work. 
I also tried using VOF proportions, expecting the gravity to create automatically the interface, but it didn't work as wel. 
Have anyone ideas for filling a tank to give an initial interface position to be simulated?
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Dear Guilherme,
If I well understood the problem, you want to simulate a filling tank process where you seek to track the interface between water and air for the jet flowing in and for the liquid part at the bottom. if this is true, than you have an open system (mass is not constant) and transient behavior. I found this video (https://www.youtube.com/watch?v=ijkpJnWyZ3c). I think you want to do similar simulations. Maybe if the initial conditions are void fraction 1 for air inside the tank and 1 at the inlet for water. Of course you need to specify the density and the gravity and its direction and the surface tension for water. this should work.  maybe this video can help you too https://www.youtube.com/watch?v=xQBvYceTg8E.
Good luck.