Computational Fluid Dynamics - Science topic

Hello, please, how can NOx (ppm) be determined numerically (using CFD ANSYS)?

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.

We're looking for collaborators in the area of CFD with application in airborne virus transmission reduction. Specifically we're interested in speech-driven airflow and the resultant downstream flow around face-shields (and possibly other types of PPE).

We're especially interested in researchers located in (and possibly around) the African region in countries that could have a full-fee discount for publishing [www.springernature.com/gp/open-science/policies/journal-policies/apc-waiver-countries].

We're currently planning our article that we intend to publish in Nature (or similar) in an 'open-access' way (Nature's 'Scientific Reports', for example. We're happy to co-author this article if we retain full intellectual freedom to continue our R&D (happy to co-design this with you).

We're independent (non-profit-y) researchers located in Australia, with motivations of health equity & disruption (without possible constraints of being more concerned with 'h-index' & similar academic paradigms). If interested or any questions, please contact us. Regards, Nick: nchowlett@pm.me

Myself Shanmukh sagar Ganesh currently pursuing M.Tech in Applied Computational fluid Dynamics in VIT, Vellore. Currently I am doing a project based on ship hull but I do not have any how to design a ship hull. So, I am searching for 3D models of ship hull. Please help me out.

Given that LaTeX formula cannot be displayed as expected here, you'd better copy and paste it into a Markdown file.

This question was proposed on Physic StackExchange yesterday (https://physics.stackexchange.com/questions/830965/how-to-determine-the-alpha-value-of-artificial-viscosity-in-smoothed-particle-hy), but was closed today because it deals more with engineering instead of physics, and is thus off-topic. So I propose it here and hope someone may help me explain it.

I am confused about how to choose an appropriate value of $\alpha$ in the artificial viscosity. The value that I deduced is far from the recommended value and led to great numerical instability.

Artificial viscosity is introduced into the momentum equation of smoothed particle hydrodynamics:

$$\Pi_{ij}=-\alpha h\frac{c_i+c_j}{\rho_i+\rho_j}\frac{\boldsymbol{v}_{ij}\cdot\boldsymbol{r}_{ij}}{{r_{ij}}^2+\epsilon h^2},$$

where $\alpha$ is a dimensionless factor, $h$ is SPH kernel radius and $c$ is the speed of sound. The artificial viscosity is related to the physical dynamic viscosity (Pa*s) by

$$\mu=\frac{\rho\alpha hc}{8}$$

for two-dimensional cases [1]. Hence, if the values of $h$, $c$ and $\mu$ are given, we can estimate the value of $\alpha$ as

$$\alpha=\frac{8\mu}{\rho hc}.$$

When it comes to the sound of speed, in order to both limit the density variation within 1% ($\delta\rho/\rho\sim v^2/c^2$) and allow an acceptable timestep (by the CFL condition), $c$ is also artificial, and customary to be $10v_\mathrm{max}$, where $v_\mathrm{max}$ is the maximal fluid velocity [2,3]. As to the case of dam break with the initial water column height of $H_0$, the estimate of $v_\mathrm{max}$ is

$$v_\mathrm{max}=\sqrt{2gH_0}.$$

So Monaghan set $c$ as $\sqrt{200gH_0}$ in [2].

Assume the initial spacing between fluid particles is $H_0/N$, and the SPH kernel radius is triple the spacing,

$$h=3\frac{H_0}{N}.$$

Now we may obtain a proper value of $\alpha$:

$$\alpha=\frac{8\mu}{\rho\cdot(3H_0/N)\cdot 10\sqrt{2gH_0}}=\frac{2\sqrt{2}}{15}\frac{\mu N}{\rho\sqrt{gH_0^3}}$$

In the case of dam break, one can assume that $\mu=1\times 10^{-3}~\mathrm{Pa\cdot s}$ (water), $\rho=1000~\mathrm{kg/m^3}$, $100\leq N\leq 1000$, $0.1~\mathrm{m}\leq H_0 \leq 1~\mathrm{m}$, $g=9.81~\mathrm{m/s^2}$, and we may estimate that

$$6\times10^{-6}\leq\alpha\leq2\times10^{-3}.$$

This is way too far from the recommended range of $\alpha$ which is 0.01-1.

And when I used the estimated alpha value to simulate the dam break, it could not converge as expected. **So, I wonder whether there is any mistake in my estimation, or any misunderstanding of the SPH theory.** Any comments or advice will be appreciated!

**References**

[1] Monaghan, J. J. Smoothed particle hydrodynamics. Rep. Prog. Phys. 68, 1703–1759 (2005).

[2] Monaghan, J. J. Simulating Free Surface Flows with SPH. Journal of Computational Physics 110, 399–406 (1994).

[3] Monaghan, J. J. Smoothed Particle Hydrodynamics and Its Diverse Applications. Annual Review of Fluid Mechanics 44, 323–346 (2012).

I am currently working on a project that involves modeling the performance of metal hydride hydrogen storage systems. A critical aspect of my research is accurately determining the real-time density of the metal hydride during the absorption and desorption phases.

I am seeking guidance on the appropriate expression or equation that can be used to calculate this real-time density during these dynamic phases (ρ_s, density of solid). Additionally, if there are any relevant resources, papers, or examples that can provide further insights into this calculation, I would greatly appreciate it.

Any assistance or suggestions would be invaluable to my work. Thank you in advance!

Hello ,

I'm starting a new position and I want to use a CDF program to get some thermo-fluid dynamics in active buimding facades (or even inside).

Do you have any recommendations on what program to use?

Note that this is going to be my first experience in such programs.

Thank you in advance.

Joseph

I'm working on optimizing the geometry of a Ventricular Assist Device (VAD) using computational fluid dynamics (CFD) simulations. My research focuses on adjusting design parameters such as blade angles, thickness, and rotor length to maximize pressure rise and hydraulic efficiency. I'm exploring various optimization techniques, including surrogate-based models and multi-objective algorithms, to achieve an optimal VAD design.

I have two questions:

I'm thinking to do some optimisation of geometric parameters using OpenFOAM to find 'best' design - for a non-profit project. Thinking of using CFD in combo with Machine Learning. Basically a massive parameter sweep using CFD then using those (hopefully) empirical results to predict in-between results via ML. Has anyone tried this before?

CFD - Mesh Generation - Grid Generation - Spatial Discretization

Dear all,

I am working on particle deposition in human's & rat's respiratory airways using CFD and I am looking for the 3D CAD file for my simulations (STEP or IGES format).

If somone has such a file I will appreciate it if he/she can share it with me.

Kind regards

Mounir

In terms of CFD, we often analyze the stability of the error using Von-Neumann analysis, especially for FDM based problems. Should we follow the same approach for a compressible fluid flow using FVM ?

Dear ResearchGate Community,

I am actively seeking a PhD opportunity in Mechanical Engineering, with a particular focus on Computational Fluid Dynamics (CFD), Advanced Materials, and Heat Transfer. I am highly motivated to contribute to groundbreaking research in these areas and am looking for a dynamic and innovative research group where I can pursue my academic and professional goals.

While deriving for a momentum equation with elastic stress effects, I am planning to put a ratio between elastic modulus (in Pa) and dynamic pressure (in Pa) in a simplified form.

I am not dealing with compressible flow or acoustics; should we still denote it as Cauchy number or modified-Cauchy number?

My equations are related to thixotropic flow where the time scale for relaxation is infinity. Hence, I am unable to use Deborah or Wi to any significance.

#Transport Phenomena

#CFD @CFD

#Navier_Stokes

#Complex Fluids

#Non-Newtonian Flow

#Rheology

Hello all,

I've got a 2D simulation case in which the flow separates from the sharp leading edge of rectangular bluff body and reattaches to the wall some distance downstream. The main goal is a accurate prediction of pressure distribution along the body's face parallel to the flow.

I'm doing a transient simulation using SST model in conjunction with gamma-Re transition model. The time- cord-averaged y+ is less than 2~3 and the inflation layer around the face of interest contains 10 prism layers. The Re number based on the body's width (perpendicular to the flow) is 1.7e+4.

The problem is that my model overpredicts the reattachment length, which in turn leads to delayed pressure recovery.

I have a suspicion that longitudinal decay of turbulence values specified at the inlet might be to blame. Consulting the Ansys CFX-solver Modeling Guide, I learnt that one solution is to prescribe appropriate turbulence values at the inlet based on the desired values at the body. An alternative approach also suggests some additional source terms for k and w transport equations in order to preserve the inlet values up to some distance upstream the body, from where decay is allowed.

Here are my questions:

1- Is my suspicion valid in the case of my problem?

2- Is the decay of turbulence of physical basis or a numerical artifact?

3- which of the two methods works better? Are there any attempts in the literature?

I appreciate your comments.

Hi! I am trying to evaluate the performance of a bypass graft using transient CFD via ANSYS Fluent. However, I cannot find a way on how to calculate and display time-averaged wall shear stress, oscillatory shear index, and relative residence time on the software? Can anyone help me? Thank you!

Keeping Computational Fluid Dynamics (particularly using OpenFOAM) post-processing in Python allows significant advantages, to my mind. Transparency (did I hack my stats models to get lovely pictures that fit the data then say can't show it because of IP?) & risk reduction (does access to foundational code go missing when some business owner gets pissed-off?), namely.

Specifically, access to a whole ecosystem of data analysis capabilities [1]: the ability to hook into R-based [2] statistical modules from Python [3], in addition to Python-based modules [4]. Can be visualised in-depth via PyVista [5].

Other's thoughts? Alternative hypotheses very welcomed!

[1] https://jakevdp.github.io/PythonDataScienceHandbook/

[2] https://www.r-project.org/

[3] https://rpy2.github.io/

[4] https://www.statsmodels.org/stable/index.html

[5] https://tutorial.pyvista.org/index.html

I am running a coarse DNS case for pipe flow with 2.1 Million cells. My residuals are quite fluctuating as its a fully turbulent annular pipe flow case but its getting statistically converged to a mean value.

My doubt is, the residual values are quite high where its mean is getting converged for instant close to 0.1 or 0.01(refer attached .png), despite of giving tolerance of 1e-06. Due to this I think I have results of velocity profiles and shear stresses quite under predicted.

what can be the possible ways to reduce these residual values?? and what is the reason of having such high residuals??

NOTE: I am already using higher order schemes for solving Fluid flow equations in OpenFOAM

What should be the Capillary Number obtained for water flow inside a silicone microchannel so that we can ignore the Capillary Effect in this study?

My study investigated forced flow with Reynolds numbers between 125 and 1300.

If our criterion for the capillary number is 1, and we consider the capillary effect non-negligible for low values of 1, according to the capillary equation, the capillary effect cannot be neglected in many conditions and cases. For this reason, I think the value of 1 is not a critical value.

Also, the denominator of the capillary number equation is related to the surface tension parameter. Is the value of this parameter equal to 0.0726 N/m, which is the surface tension between water and air, or should we put the surface tension between water and a solid wall (silicon)? In many research studies, authors have used the value of 0.0726 N/m.

Ca=μ*U​/σ

"How do advanced computational modeling techniques, such as finite element analysis or computational fluid dynamics, aid in the precise characterization and optimization of thermal bridging phenomena within complex building assemblies?"

In CFD simulations, determining the appropriate inlet and outlet boundary conditions is crucial for accurately modeling recirculation phenomena in both two-dimensional (2D) and three-dimensional (3D) scenarios.

For recirculation simulations, the inlet boundary condition typically involves prescribing the flow properties entering the domain. This may include specifying the velocity profile, temperature, turbulence characteristics, and any other relevant parameters. In 2D simulations, the inlet boundary condition can be defined as a 2D plane through which fluid enters the computational domain. In 3D simulations, this boundary condition extends to a full 3D volume or surface. In both 2D and 3D simulations, accurately representing the inlet and outlet boundary conditions is critical for capturing the complex flow dynamics associated with recirculation zones. Properly defined boundary conditions ensure that the simulated flow field closely matches the real-world behavior, thus enhancing the reliability and accuracy of the CFD predictions.

hello Everyone,

if I want to study, coal combustion in different atmospheres for example in O2/N2 and O2/CO2. I obtain the kinetics of both atmospheres using Hetrogenous models. ( Shrinking core model ) and Random pore model.

I was wondering if it’s possible in CFD to study particle profile. Does the heat transfer affect in CFD will calculated based on the Gas composition input or I should add something in UDF file.

FYI, the reaction models are based on conversion so I am not really sure how CFD will identify the differences in Atmospheres.

further, I wish If I found a sample UDF file that been used for Hetrogensous models.

Ahmad

Hello Everyone,

I have some queries about if its possible using heterogeneous models reactions to model particle Temperature profile in CFD ?

I performed Kinetic analysis of my reaction (coke oxidation for example) my only concern what should I do in CFD. Also Let's say I am performing the reaction into two atmosphere, how the CFD will identify the reactant since heterogeneous model are based on conversions.

This is a code block from nutWallFunction library in OpenFOAM where in, effective kinematic viscosity ($\nut_w$) at the wall is calculated using resolved field(in case of LES)/ mean field(in case of RANS) and $y^+_p$ (wall normal distance of the first cell center). this allows to set a new viscosity value as boundary condition at the wall using log law. Considering the first cell center is in the logarithmic layer of the universal velocity profile.

Now, in this code block of member function defined as nutUWallFunctionFvPatchScalarField::calcYPlus()

There has been iterations done for the yPlus value to reach convergence with maximum of 10 iterations. Why are these iterations needed? and why is the maximum number of iterations 10. I have given a reference of the code below;

tmp<scalarField> nutUWallFunctionFvPatchScalarField::calcYPlus

(

const scalarField& magUp

) const

{

const label patchi = patch().index();

const turbulenceModel& turbModel = db().lookupObject<turbulenceModel>

(

IOobject::groupName

(

turbulenceModel::propertiesName,

internalField().group()

)

);

const scalarField& y = turbModel.y()[patchi];

const tmp<scalarField> tnuw = turbModel.nu(patchi);

const scalarField& nuw = tnuw();

tmp<scalarField> tyPlus(new scalarField(patch().size(), 0.0));

scalarField& yPlus = tyPlus.ref();

forAll(yPlus, facei)

{

scalar kappaRe = kappa_*magUp[facei]*y[facei]/nuw[facei];

scalar yp = yPlusLam_;

scalar ryPlusLam = 1.0/yp;

int iter = 0;

scalar yPlusLast = 0.0;

do

{

yPlusLast = yp;

yp = (kappaRe + yp)/(1.0 + log(E_*yp));

} while (mag(ryPlusLam*(yp - yPlusLast)) > 0.01 && ++iter < 10 );

yPlus[facei] = max(0.0, yp);

}

return tyPlus;

}

My doubt is concerning the do-while loop at the end for yPlus iteration.

I need to use computational fluid dynamics software to obtain wake data for LHA ship, and I would like to get your help.

I am new to limiters in FVM CFD so pardon me if its a blunder. Was curious about Venkatakrishnan's limiter (first image) that is industry standard in many commercial CFD solvers. He came up with the final form as given below and further modified the Δ_ term in order to avoid division by numerical values close to zero. Why not eliminate Δ_ term by taking out one from the numerator(second image)? Any advantage of writing in this form(first image)? ref: 10.1006/jcph.1995.1084

ref:

Low Prandtl number fluids like air, Pr <1, takes very long endTime for simulation to get the fully developed convection cells pattern and thermal boundary layers. What is the possible reason for this? Is it solely because of the dependency on kinematic viscosity (numerator of prandtl) being very low? Or is this related to simulation case setup.

Dear Friends,

I am looking for a faculty or Engineers or others who are interested in working on CFD of multiphase flow in chemical engineering reactors for collaboration research. Please contact me on Facebook messenger or text and call on +9647713171293.

Associate Prof Haidar Taofeeq

Can we do it on COMSOL or Ansys (CFD)?

Please can you clarify about this question.

computational approach

I am in search of commercial Computational Fluid Dynamics (CFD) software tailored for modeling hydraulic structures, particularly for applications related to stormwater, small dams, flood control structures, channels, and similar scenarios. The primary focus will be on studying free-surface flows. Affordability is a crucial consideration in the selection process. While I am already familiar with Flow-3D, Ansys Fluent, and Ansys CFX, I am open to exploring additional software options. I would appreciate any recommendations for alternative applications, and it would be beneficial to receive insights on various features to facilitate a comprehensive comparison for making an informed decision.

Hello everyone, I'm working on a CFD analysis to compute wind pressure coefficients (Cp) on a building facade. My objective is to use these Cp values in EnergyPlus AFN to evaluate the impact of natural ventilation on thermal comfort. While reviewing various studies that have undertaken similar work, I've encountered conflicting information regarding the parameter Uref. I encountered some sources that recommend default values of 10 m/s for Uref and 10 m for Zref. Nevertheless, some research papers suggest that the dynamic wind pressure (Pd) necessary for Cp calculations should be determined at the building height. Moreover, one source suggests setting Uref as "the largest freestream velocity at the top of the [wind tunnel] modeling domain". My analysis involves a parametric design, exploring different building heights. So I suppose I need to establish a consistent reference height for all simulations. I've already obtained weather data containing wind speeds and directions and have calculated average wind speeds at a height of 10m for 12 different directions. My question is whether these averaged values should be directly input as boundary conditions for the cylindrical domain or if I should stick with a fixed value for Uref, like the mentioned 10 m/s. Any guidance to clarify this matter would be greatly appreciated.

I wonder if there is a document like tutorial that is useful to simulate an Archimedes Screw

Hello, the Research community,

I'm currently working on a project involving heat transfer between a solid domain and a liquid domain using Ansys Fluent, and I'm facing some challenges. Here's a brief overview of my setup:

I aim to simulate and analyze the heat transfer process between the solid domain walls and the flowing liquid. I'm seeking guidance on the further steps to solve this problem effectively. Specifically, I'm looking for advice on:

I would greatly appreciate any insights, tips, or step-by-step guidance from those with experience in conducting heat transfer simulations in Ansys Fluent. Your assistance will be invaluable in helping me advance my project.

In addition, kindly guide me through the necessary steps to create an effective heat transfer interface between the solid and liquid domains in Ansys Fluent. Any insights, tips, or tutorials to help me set up this heat transfer simulation would be greatly appreciated.

Thank you in advance for your assistance.

Thank you in advance for your support.

Best regards,

Sudeep N S

I would like your expertise and guidance regarding a challenging Computational Fluid Dynamics (CFD) problem I currently have. The project involves species transport in Ansys Fluent, focusing on simulating a steam methane reforming process.

The issue I am encountering pertains to the Chemkin files that I have uploaded into the Ansys Fluent software. Unfortunately, I am encountering persistent errors, and it seems the software is not properly considering the uploaded Chemkin files. I have thoroughly reviewed the inputs, but the problem persists. Despite my best efforts, I have been unable to resolve this issue.

Furthermore, in this simulation, a key aspect involves maintaining a wall at an elevated temperature of 2000 degrees Celsius. The objective is to facilitate heat transfer to the methane and steam feed mixture to initiate the steam methane reforming reaction.

Regrettably, I have observed that the heat is not effectively transferring to the feed mixture, resulting in the absence of the desired chemical reaction. This poses a significant setback to the project, as the core objective is to study the reaction kinetics and product distribution in this specific environment.

Your support in this matter would be immensely important to my research progress.

Thank you in advance for considering my request. I am eager to learn from your expertise and am open to any suggestions or instructions you may have.

Sincerely,

Sudeep N S

FORTRAN in CFD Solvers

Hello dear all,

We want to set-up a CFD -Discrete Particle Modelling case for a bubble column where liquid is eulerian and gas bubbles and solid particles are discrete phases (three-phases total holdup <10 %) as given in attached diagram. In this case only gas bubbles are flowing with velocity UG <1 cm/s while liquid and solid particles have no initial velocity (means batch mode). Boundary condition (DPM) for gas phase at outlet is pretty straight forward "escape" but we want to retain second discrete phase "particles" with in column volume. However, Boundary condition panel in Ansys Fluent do not show "escape" or "wall" or "reflect" for an individual DPM (injection) phase but one for all DPMs.

We want to model the effect of gas bubble induced flow behavior (in one-way coupling) on liquid and solid phases, so we need to keep liquid in batch mode and solid phase (one-time injection). Any suggestion on how to set-up DPM-BC for two discrete phases (two different injections) separately in Ansys Fluent?

How can we optimize the flow & consumption of fuel in Aerospace sector using CFD ?

Detailed suggestions are needed with tutorial link etc.

Dear CFD Researchers,

Since AI tools are currently very popular, I am wondering if anyone use them to choose turbulence model for a CFD case.

So if you did, please share your experiences. Due to the answer, we can extend the boundaries of this discussion.

Thank you for your comments.

Kind regards,

Guven

Hello all,

I'm doing a 2D simulation of flow beneath a partially-submerged rectangular bluff body. The problem's geometry is shown in the figure attached. I'm using a fully structured hexahedral mesh with a y+ of below 1. When the draft (i.e. t in the figure) is small, the model predicts the reattachment length (i.e. Lr) quite accurately. However, it leads to excessive reattachment lengths for cases of large drafts.

As the draft increases, I wonder what turbulent mechanisms/characteristics become influential that SST fails to capture properly. Could it be the increasing curvature of the streamlines or probably turbulence anisotropy? I appreciate any insights.

Regards,

Armin

Hi everyone. I have some problems about evaporation - condensation. (This is very long question :) )

I am trying to simulate water evaporation for different designs but actually I can't.

I'm a relatively newbie in liquid-gas two-phase simulations, especially in Fluent. I'm trying to simulate evaporation and condensation that occurs at every temperature, not boiling. I can't get the right result when I run my models by trying the VOF and mixture models.

The methods I have tried so far and the methods I did not get results:

I defined three phases (air, water-liquid and water-vapor).

1. I created a piecewise - linear graph for saturation temperature by choosing water to steam as the mass transfer. There was no evaporation. Also, if I choose steam to water, I got a negative latent heat error.

2.While researching, I tried creating source terms for cell zone, liquid and vapor. Simply, if t>t_sat was evaporation, if t<t_sat was condensation mechanism, they were udfs. I added define properties(saturation_temp) in udf, but I don't know if I made a mistake in Fluent, I couldn't Run the simulation. (Even if evaporation-condensation started somehow, the mass transfer rates were not correct.)

3. Lastly, I watched solar still videos on YouTube and tried to reproduce it. I tried to do exactly the same things, but what people do either doesn't work or even if the simulation works, evaporation at low temperature doesn't start.

To conclude; I need tips, a step-by-step guide, or the right UDF files to get to the right model. I am open to any help. 😊

If I don't get a result, I will try with OpenFoam, but my priority is Fluent because of my colleagues' Fluent experience and habits. (Another reason is that Fluent seems to be the easiest way for us to transferring this experience to our students when necessary.)

Turbulence structure is described by the formation of eddies. Size of eddies vary based on the turbulence length scale ( (Kolmogrove, Reynold and Hinze). Smaller eddies describes intense turbulence, larger eddies display low turbulence zone.

Recently, I came across a book by Bertin and Cummings, which says there are no physical laws to describe detailed turbulence structure pattern.

Are there any ?

Hi All,

Question: How do I get Mach No contour for CFD Post-processing?

What could I try?

Any help is appreciated.

Thank You,

Alin

I'm currently facing negative cell volume detected error because of weird mesh deformation, ig I might have made mistake in the dynamic mesh setting but I'm unable to pin point my mistake. Also the simulation occurs for a few time steps with ridiculous values of lift and drag coefficients. I'm attaching below the pictures of deformed mesh, lift, drag coefficient curves, my smoothing and remeshing parameters too. Also I'm using a udf to give motion to the cylinder body. The frequency defined in the udf is 1. I had created a total thickness inflation mesh around my cylinder which is of 5 layers, growth rate of 1.2 and maximum thickness of 0.025. Hence, I first separate the cylinder along with the 5 layered inflation from the surface body, then I give the udf motion to both the cylinder and the 5 inflation layers that I had separated. Kindly help me regarding this issue as I've been trying to solve this issue since past 3 weeks, took reference of changing the time step from various articles but still I get the same error.

I'm running a surface reaction. I'm wondering how does ANSYS Fluent calculate the surface deposition rate?

Thank you.

I'm trying to simulate VORTEX INDUCED VIBRATIONS in Flow Around A Rigid Cylinder. The diameter (D) and mass of the cylinder are 0.5 m and 35.78 g, respectively. The spring stiffness is 69.48 kN/m, the damping coefficient is 0.0039 Ns/m and Re=200. I've been trying various UDF since past 2 weeks but everytime m not able to simulate any oscillation so it would be of great help if you kindly provide the UDF.

This research aims to investigate the dynamics and properties of accretion disks around black holes using Computational Fluid Dynamics (CFD) simulations. Accretion disks play a crucial role in astrophysics, and understanding their behavior is essential for studying the physics of black holes and their associated phenomena. The proposed research will employ CFD techniques to model the complex fluid flow within the accretion disk, considering factors such as viscosity, magnetic fields, and relativistic effects near the event horizon. The simulation results will be analyzed to gain insights into the disk's structure, energy transport mechanisms, and radiation emissions. The research findings will contribute to advancing our understanding of black hole accretion processes and their impact on astrophysical phenomena.

Please, are there any CFD software applications that can be used to generate an O-grid mesh for airfoil flow simulations apart from pointwise?

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

Hi guys

Can anyone model the water spray from the tiny holes in a tank exposed to a hot, high velocity external flame using CFD? What commercial software do you recommend?

thanks

It would make my essay easier to find information about this airfoil.

Thank you anyway!

#naca #aviation #engineering #airfoils #pilots #2430 #information #wind turbine #CFD

I've worked on simulating 3D VIV (a cylinder forced by Karman vortex street) and been stuck with settings. Considering the transition to turbulence due to the oscillation of cylinder (Re≤200, laminar upstream), "SST k-ω coupling with intermittency transition" is my scheme now.

However, I'm not sure whether I should enable "intermittency transition" since I don't fully understand the statement given in the user's guide, which says "The Transition SST model is not Galilean invariant and should therefore not be applied to surfaces that move relative to the coordinate system for which the velocity field is computed; for such cases the Intermittency Transition model should be used instead."

I don't understand the bold sentence in the statement especially. Does it mean the moving surface of cylinder (in my case)? Hope anyone can provide any guideline. Thank you so much.

Hello everyone!

I'm doing CFD propeller marine. But I am errored. Can you help me?

Error at Node 0: floating point exception

Error at Node 1: floating point exception

Error at Node 2: floating point exception

Error at Node 3: floating point exception

Error at Node 4: floating point exception

Error at Node 5: floating point exception

===============Message from the Cortex Process================================

Compute processes interrupted. Processing can be resumed.

==============================================================================

Error: floating point exception

Error Object: #f

Registering ReportDefFiles, ("C:\kp_files\dp0\FFF\Fluent\.\report-file-0.out")

Calculation complete.

So I usually use the COMSOL Multiphysics software to deal with hemodynamic problems with the CFD module of the software. i found OpenFoam as a opensource software but i don't have ideas about it.

is OpenFoam suitable for scientific reasearche in matter of medical field?

what are the major difference between Ansys Fluent, Comsol Multiphysics and OpenFoam?

are the results obtained with OpenFoam equivalent to thous obtained with the commercial software ?

thanks in advance

Hello,

I wish to solve the weak N-S eq (based on PDE's) in COMSOL.

By default, COMSOL applies the equation in all domain but I want to solve it in each mesh (not all domain).

I want to do this in order to add different porosity in each CFD mesh.

Is it possible?

Thanks in advance.

Which software is mostly preferred in research for preprocessing during CFD analysis and gives best results?

G'day,

I'm working on simulating 3D Karman Vortex Street, confused how to distinguish laminar and turbulence. As the pic shows (this is a frame before starting oscillation), there is downwash near the top of the cylinder, but the Reynolds number in this case doesn't exceed 200, namely, it should be laminar. ----------------update--->

Yesterday, I asked Perplexity Ai to find some info and it provided some reference talking about the wake structure due to the end of finite cylinder. So now I just want to collect your suggestions, since it seems no reference directly indicates "the downwash is inherent no matter the flow is laminar or turbulent". So if anyone knows relevant paper, please let me know, thank you so much!

[1]

Hello, I'm COMSOL newbie working on cluster computing.

I'm using distributed parametric sweep mode, in which each server node solves a single problem (ex. Node 1 - Inlet fluid velocity 1m/s, Node 2 - Inlet fluid velocity 2m/s, etc...)

In distributed parametric sweep mode,

(1) I want to monitor multiple convergence plots since multiple problems are solved simultaneously. But I can only monitor a single convergence plot... Please give me some advice.

(2) How can I monitor multiple probe plots (which are Probe parameter - Iteration number plots)? I can only monitor the accumulated probe table, which is the final converged value. But I want to check the probe value trend with respect to iteration number.

Thank you very much!!! Every comment is my energy please help me!

I am working on BioFluid Dynamics. Ansys CFD Post doesn't have an option to plot AWSS and OSI directly like wall shear stress(WSS). So I am unable to plot this. In hemodynamics, it is an important parameter. Can anyone help how to add AWSS and OSI in CFD Post?

Hi, I am modeling sloshing of a fluid inside a container using ANSYS Fluent. For this, I am using VOF model. I consider two accelerations. a_x=2 m/s² and a_z=9.81 m/s². The modeling continues for 2 sec. Physically, a container with a liquid inside under constant acceleration will have a steady inclined surface after sometime. However, the surface that I get fluctuates. As it is shown in the image (it is just an indication), the flat surface reaches to max inclination until t=0.8 sec. After that the surface starts returning to its original flat horizontal condition and again starting going up. Could you please let me know what is the problem? Thank you,

I'm doing a 2D transient simulation of turbulent flow past a sharp-edged rectangular bluff body. I'm using a version of k-omega model for turbulence modeling. My objective is the time-averaged flow field; I'm not interested in the instantaneous field. The problem is that I'm not sure how to choose an efficient timestep size.

In the literature, i have come across two methods in this regard:

(a) The timestep is adjusted repeatedly to ensure a max/rms Courant number, or

(b) based on an estimation of the Strouhal number (associated with the dominant frequency of vortex shedding) known from previous experiences, the timestep size is determined such as to resolve each vortex shedding cycle through n temporal increments.

The problem is that, i couldn't find any consensus in the literature over appropriate values for max/rms Courant number or n in either methods. I understand that this should be really addressed through a sensitivity study, but I have very limited computational power to afford that, especially given that it takes a long time for the simulations to reach a statistically converged solution. I am hoping there's some reliable rule of thumb or related studies to use, thereby avoiding such a sensitivity analysis.

I would appreciate your comments.

i have a problem with reaction modeling by Ansys Fluent. when i change the Arrenius parameters, nothing change and it makes me confuse. can anybody help me?

Dear ALL,

What project do you recommend for CFDer not software engineer to improve coding skills, Is leetcode a good choice?

In addition, what strategy do you recommend for reading others multiple-file code? Debug and see the stack?

Thanks in advance.