Science topic

Computational Fluid Dynamics - Science topic

Numerical methods to solve and analyze problems that involve fluid flows.
Questions related to Computational Fluid Dynamics
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I am doing research in CFD and currently using RK Gill. Can you suggest a better method?
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CFD is the simulation of fluids engineering systems using modeling and numerical methods.
CFD is a set of PARTIAL differential equations - PDE’s, describing conservation laws for transport of mass, momentum and energy.
CFD is the solution of such fluid dynamic problems by means of computer based simulation
Components of a numerical simulation are :
• Mathematical model
• Discretisation method
• Coordinate system
• Computational mesh
• Approximation
• Solution method
• Convergence criteria
CFD code consist mainly of three modules:
• Pre-processor- problem formulation and mesh construction
• Solver- solution of discretisation of governing equations
• Post-processor- analysis and display of results
The continuous Initial Boundary Value Problems - IBVPs are discretized into algebraic equations using following numerical methods :
• Discretization methods
• Solvers
• Numerical parameters
• Grid generation and transportation
• High performance computation and post processing
Discretization methods are as follows:
• Finite difference method
• Finite volume method
• Finite element method
Types of CFD Codes;
1. Commercial codes:
a. FLUENT
b. STARCD
c. CFDRC
d. CFX/AEA
2. Research codes:
a. CFDSHIP-IOWA
3. Public domain codes:
a. PHI3D
b. HYDRO
4. Grid Generation and Visualisation codes :
a. GRIDGEN
b. GAMBIT
c. TECPLOT
d. FIELDVIEW
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Is there any benchmark problem to study the fluid flow behavior in the elbow using a computational method or any publication on experimental study of fluid flow in the elbow.
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please refer to this attachment, experimental work on the elbow. TQ
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Is it possible to diagnose a disease from mechanical properties of blood ?
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In computational hemodynamics, usually the blood flow is modeled by Non-Newtonian model (e.g. Carreau–Yasuda model), where the non-linear relationship between shear rate and viscosity could be established. Then, the wall shear induced by the blood flow imposing on endothelial cells can gradually change the alignment of the cell pavement and trigger some pathology of atherosclerosis. Thus, the viscosity modelling plays an critical role in computational hemodynamics.
Therefore, the rheological properties of blood is very important in prediction and diagnosis of atherosclerosis and other vascular diseases.
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I have been working on rotor and propeller blade modifications that shift L/D and also Cd at high and low AoA respectively. The work is focused on rotorcraft at present, with rotor diameters from 25' to 65', symmetric and asymmetric blades. Are there any testing programs involving HAWT blades with diameters from 60' through to 180'? The boundary layer modification that is being employed indicates that some rotor models such as Camrad II are not suitable to a CFD analysis of the dynamics involved.
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Arturo, COMSOL becomes constrained at higher Re values to being RANS rather than a DNS. This results in limitation of the validity of the outcome. In principle it would otherwise permit the evaluation of the development of a vortex filament on a surface subject to radial acceleration. Thanks for the thought.
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I am doing a CFD analysis of from part of motorcycle geometry, and I need to verify data i have obtained in turbulent model in order to progress further. I have been looking online, but I havent found any data related to which i could compare with. Is there any other way to verify what i have computed?
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Dear Gintas,
I think the best thing is to first test your code against some simple standard benchmarks, eg flow in a lid driven cavity or similar simple problems for which there are plenty of data available. Of course the closer the test problem to your physics the better. Then you can at least claim that your code is doing the right thing.
There are of course standard methods like grid and time independence studies and also methods to measure the uncertainty in your calculations. I have used a method due to Celik in my recent paper IJHMT 04/2013; 59:219-229 where you can find the reference. Additionally you can use AD (automatic differentiation) to estimate the sensitivity of your calculation to say, for example k-epsilon model parameters.
Although non of these mean that your calculation is absolutely right but at least give you some confidence in your simulations. At the end of day the only way to be absolutely sure is to validate your results against experiments or theory but when there is no experimental of theoretical studies available then you may just publish your results and the community ill decide weather you results are useful or not...
Hope this helps
sina
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I am looking for software for wind simulation for Mac OS. I use Ansys but I heard that there is no version for Mac. Is there any other software that you are satisfied with using? Is there a free version for students?
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By the way... virtual machine consume lot of resources.
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The equivalent sand grain height approach is widely used in modern Computational Fluid Dynamics (CFD) calculations on rough surfaces. I am conducting a few simulations against available experimental data on a rough aerofoil. The experiment reported the rough surfaces were sandpaper P80 and grit 36 without mention the equivalent one. Surface roughness research is not a field I'm familiar with, because I concentrate on roughness modeling in aerodynamics. So I tend to ask if any one who knows any data or correlations to sandpapers. Don't mentioned the method in Boundary Layer Theory by Schlichting, because the experiment didn't provide me sufficient data to use that. Dirling's correlation is also not viable because I can't do the roughness geometrical measurement.
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I am working on optimising the design of the static guide vanes found encasing a vertical wind turbine however I am finding it difficult picking out aerodynamic theories that would be relevant to this area of study. Any suggestions would be welcome.
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We have done a lot at our department in the Otto von Guericke University Magdeburg to optimize the Savonius turbine. Send me an email, I can send you a doctor thesis.
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What is the right way to change the moisture content of the grain from wb% to mol/m3 to put the initial and equilibrium moisture contents in COMSOL?
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These equations can be put directly as an expression in COMSOL, it will do the rest of the calculation.
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I am modeling the transesterification of vegetable oil and i am interested in the use of OpenFOAM to couple the flow and reaction. Is there anyone who has experience with OpenFOAM for reactive mixing?
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I would like to find out a simple model for solving Saint Vanint equation in 2d. Is there a free software can do this?
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Any basic book to understand the code of a Lattice Boltzmann Solver for CFD? I basically want to use XFlow.
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There is the book "The Lattice Boltzmann Equation: For Fluid Dynamics and Beyond" by Sauro Succi, which is a standard reference. If you just want to download a summary from the web try http://www.ndsu.edu/fileadmin/physics.ndsu.edu/Wagner/LBbook.pdf
Myocardial Blush Grade and TIMI myocardial Perfusion Grade
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I have read that the visual assessments of Myocardial Blush Grade and TIMI myocardial Perfusion Grade methods is categorical, subjective and operator dependent. Will you agree this. Please explain what is meant by categorical and subjective?
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The Euler equation is used with vorticity confinement methods.
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Do you mean the Euler's equation of inviscid flows? viscosity is assumed zero for an inviscid flow and Re is not defined
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I have to simulate a feed nozzle design for FCC (Fluidized Catalytic Cracking) column in a petroleum refinery. It is a multiphase problem. For this, I am asked to choose the most appropriate simulation package b/n COMSOL and FLUENT?
Can anyone help me in this regard by sharing your views on which is best for solving such cases?
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Attachment.
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Considering a fully developed flow in an annular pipe. The velocity is only a function of radius. What a bout the pressure? I know the pressure is a function of pipe length. Is the pressure also a function of radius?
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pressure drop is the driving force to push fluid to flow through a pipe, that means as far as there is no pressure difference between two points along the pipe length there is no flow. Generally pressure drop takes place even radially, but the value is too smaller than that in length. therefore we just consider the pressure drop in pipe length.
when you have a fully developed flow it doesn't mean that there is no pressure drop, it just means there is no velocity difference along the axis where we have fully developed flow.
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As we know, the Nusselt number for an isothermal flat plate is written as Nu=h*x/k where h is the convective coefficient, x is length and k is the thermal conductivity of the fluid. In addition: h=q/(Tw-T_inf) and q=k*dT/dy at y=0.
Now, if the thermal conductivity is a function of temperature, then, the thermal conductivity of free stream (k_inf) is different from thermal conductivity at the surface (k_w). For q and Nusselt which k is adequate? I believe that for q we should use k_w and for Nusselt we should use k_inf. Because q is calculated at the plate, but Nusselt is calculated regarding to flow. However, in some papers (not all of them) i see that they used k_inf for both of the Nusselt and q.
What is the best definition for Nusselt number and why?
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Hi mohammad,
don't have experience in that specific case but as far as I know a local Nusselt number can always be calculated by an energy balance on the surface in this case you only need k_w. But obviously dt/dy|_w changes and so does Nu_x.
I have used a similar approach in the following paper: International Journal of Heat and Mass Transfer. 01/2013; 59:219 - 229. for calculating the local Nusselt numbers around a cylinder. Of course k was a constant in that case but this doesn't change the formulation.
For a simulation it would be quit easy to calculate dt/dy and correspondingly the local values of the Nusselt number then you can integrate this for a mean Nusselt number. Of course it is possible to use an average temperature to advise a mean Nusselt number but then the question is how to calculate the film temperature (1/2 1/3 and other suggestions).
Anyway for engineering purposes I guess using a film temp and an average k would be just fine.
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I need some suggestions on CFD Analysis of microturbine ( speed above 1,00,000rpm)..
i am planning to use ANSYS-CFX as i need to proceed with FSI of blades after getting forces from CFD..
Details- Curved blade rotor, 8 blades, axial flow, clearance btw wall 1mm.
I am planning to use sliding mesh to the rotating interfaces since unsteady conditions may exist.
My Query- How to mesh fluid and solid region, whether rotating parts alone meshed separately or stationary volume also need to be meshed along with it..
Does it requires to define the boundary btw blades and hubdisk since both are rotating..but separate..
I am using Sliding mesh for first time,, looking for some tips
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Hi there.
I have been working on Microturbine Generation system modelling and simulation using MATLAB. I'm getting speed about 2,73,000 rpm when connected to permanent magnet synchronous generator. As i'm from electrical field, i couldn't able to understand the basics of those control blocks (temp control, radiation shield, exhaust temp, fuel valve actuator...). Could you please help me out?
And i saw one thesis for your CFD analysis...I can forward that copy if you're interested.
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Give your personal opinion for others to read.
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I did not elaborate in my earlier comment because I thought most people are aware of h index and impact factor. But it seems it is necessary to say a few things.
By and large, impact factor relates to quantification of the quality of a Journal whereas h factor to that of an author. A journal has higher impact factor if it has more readership and thus popular. Now we know all over the world the number of scientific community is much more in biological and medical sciences. In physics it is not that big. In chemistry still there is large community. Therefore the impact factors f journals in physics remain low as compared to those in medical and biology fields. Now a days there is a tendency to have broad based generals like "biomedical and materials" having high impact factors because the audience they cater to is very large. Anyway this has become a technique to increase impact factor o a journal. The classical journals in physics who are well rated like Physical Review do not get their impact factors increased very much above 3. Still they have their place in the society of physicists.
As regards h index, it has not much to do with impact factor of a journal directly. It only is an indicator how many of your papers are cited how many times. It does not depend on the quality of who cites them or which journal cites them. In big groups this h index tends to rise enormously because all collaborators refer invariably the group citations and continues endlessly.
Of course there is a problem for a relatively new entrant to establish and find ppl who can cite his/her work. It seems one has also to be smart in addition to good worker.
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This book required for beginners only.
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I am also searching a book? If you have please inform me.
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Other than matlab
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For symbolics Wolfram Mathematica is considered very useful, I prefere MathCad from PTC for engineering calculation. Wolfram has very nice site with examples and manuals, as well does PTC online community. Many fields are thoroughly researched and published in unofficial way on community forums in form of codes. Sage is nice tool and also open source, not so fancy like Mathematica but useful and free. Matlab is good for huge amount of data and has many functions, but not good for symbolic calculations like Mathematica and not so friendly using physical units like Mathcad.
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I wish to make a simple program that solves tridiagonal matrix . now TDM can be solved using Thomas' algorithm, which is very serial in nature. I have come across cyclic reduction , even-odd reduction method in one of nvidia's papers. Can some one please explain me this algorithm, and help me with the pseudo code?
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NVidia's cusparse library
appears to provide a tridiagonal solver
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I am working now on the grain drying with CFD simulation using Comsol and I need to start with one kernel simulation for moisture transfer during drying. This is the first time for me to use the Comsol. So, How can I start?
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please have a look the following paper:
Kumar, C., M.U.H. Joardder, T.W. Farrell, and M.A. Karim, Multiphase porous media model for intermittent microwave convective drying (IMCD) of food. International Journal of Thermal Sciences, 2016. 104: p. 304-314.
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The gate opening time in experiments exceeds the required time for a sudden dam-break (0.3 sec instead of 0.17 sec). Numerical results match with exp data for the laminar flow condition for the k-epsilon model.
Can this be correct?
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Hello, you have also a comparison between numerical and experimental dam-break flows on wet bottom in this publication :
Three-dimensional Large Eddy Simulation of air entrainment under plunging breaking waves
Coastal Engineering, Volume 53, Issue 8, June 2006, Pages 631-655
Pierre Lubin, Stéphane Vincent, Stéphane Abadie, Jean-Paul Caltagirone
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I made a model on CATiA V5 and I am facing difficulty in doing the analysis part. I really do not know how to do the analysis. I haven't used Gambit or fluent before.
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You can export your file with *.stp after then open ANSYS Workbench and select "Fluid Flow (Fluent)". Now import file in "Geometry". Then you can create mesh with the mesh section. Then you can select boundary condition in "setup".
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I have been trying to simulate droplet falling, impact and spreading. I have used COMSOL and Fluent. I got some results but they are not satisfactory. Is there anyone who worked on similar things? I need to :
1) define an initial velocity of the droplet
2) apply dynamic contact angle during spreading
For COMSOL, the droplet don't deform that much after the impact.and for fluent I having trouble defining a free / open boundary. I have been using pressure inlet for free boundary. Here is some simulation result.
1. VOF+Level Set - with surface tension - with wall adhession (https://www.youtube.com/watch?v=P4VkHX9UYeE)
2. VOF+Level Set - with Surface Tension - no wall Adhession (https://www.youtube.com/watch?v=4UVQ-AM-vkY)
3. VOF (no Level Set) - without surface tension - no wall adhession (https://www.youtube.com/watch?v=rtVbNEHD6zE)
Can anyone help me regarding regarding my queries?
1. How can I assign initial velocity for the droplet?
2. How can I get more realistic deformation?
3. How can I apply wetted / non-wetted surface condition?
4. How do I implement dynamic contact angle?
Can anyone tell me whether Smooth Particle Hydrodynamics (SPH) is a better option for this problem?
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I think those droplets are big enought that you should be able to use the Stoke's settling velocity as a decent estimate, though less than about twenty microns might need a better estimation. Ther teminal velocity of the 100 micron and smaller droplets is surprisingly slow. Down to about 10 microns they fall so slowly that I suspect the surface tension is going to overwhelm much of your other deformation simulations.
A good first step might be to plot your settling velocity for your range of particle diameters. (They're droplet shaped, but you can use the aerodynamic diameter, which is basically the average diameter.) I suspect that you're going to see that you'll need a few different simulations for the impact and spreading.
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I have a reasonably complex experimental electro-mechanical hydraulic system (using water medium) design I would like to have simulated (to include pressure and flowrate versus time response, valve operation - steady state and transient) before I spend a lot on hardware to build it. If anyone has any connections/suggestions, please let me know.
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Thanks to all for links, etc., but I really need an expert to do this study, rather than software...anyway, I posted the job on a freelancer site and seem to have found someone.
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I looked up through the literature and I ended up with a work done by Olsen H. and here is the citation "Olsen, H. (1970). Unpublished sloshing experiments at the Technical University of Delft. Technical report, Delft, The Netherlands." However, I was not able to get this reference.
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Here are few references:
[43] G. G. Stokes. On the theory of oscillatory waves. Transactions of the Cambridge
Philosophical Society, 8:441–455, 1847.
[44] G. G. Stokes. Mathematical and Physical Papers. Cambridge University Press,
pages 197–229, 1880.
[45] I. A. Svendsen. Introduction to nearshore hydrodynamics. World Science Publishing
Ltd, 2005.
[46] J. M. Vanden-Broeck and M. C. Shen. A note on solitary and cnoidal waves
with surface tension. Journal of Applied Mathematics and Physics, 34:112–117,
1983.
[47] G. R. Whitham. Nonlinear dispersion of water waves. J. Fluid Mech., 27:399–
412, 1967.
[48] A. S. Peters and J. J. Stoker. Solitary waves in liquids having non constant
density. Communications on Pure and Applied Mathematics, 8:115–164, 1960.
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Because Fluent is a commercial code, it is not always good to use the default turbulence model inside for research purposes. To define an omega equation based turbulence model, in Fluent, we can choose the k omega model, define our own user defined scalar (UDS) transport equations, and then solve the newly defined transport equations instead of the default k omega model. The k and omega values are also necessary to be copied back to the default k and omega field, because the momentum and energy equation needs the value of k and turbulent viscosity (computing the unknown Reynolds stress) as well.
So, my first question is, is there anyone has done similar things before?
I managed to write an UDF to define all necessary UDS, boundary conditions, and initialization, but I find the k and omega jump to negative values in some region of the flow field. Linearization of the source term, limiters for k and omega may help, but I don't exactly know how to do it. So, my second question is, how to deal with the solution divergence when using UDS k and omega equations.
My ultimate goal is to define all k omega based turbulence models, such as SST, and γ-Reθ SST.
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Hi Ali,
Have you got your UDF to work? I downloaded it and tried to run a simulation with it and received errors
what does plane wave solutions to a coupled system of differ.eqns indicate? Do the show any relation with integrablity or symmetricity of Differ.eqns.
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vivek sharma NMiMs,Mumbai.
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I am researching biomimetics of fish and sea creatures, especially their motion. Any paper, documentary, or piece of information would be useful for me.
I am trying to understand the idea behind motions of fish and sea creatures, regarding efficiency and hydrodynamics.
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Hi,
you can also check this out:
around minute 25 of the film you have some simple examples
Hope this will help
Andrei
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It can be any type of DNA like pUC18. The DNA should change it's location with time when a force will be applied to the microfluidic device like electric force, magnetic force etc.
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I want to model the propagation of a flame front using MATLAB. What model can be used? Any references from where I can get information?
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Try this book: "J. Warnatz, U. Maas, R.W.Dibble. Combustion. Physical and Chemical Fundamentals, Modeling and Simulation, Experiments, Pollutant Formation. ISBN-10 3-540-25992-9. Springer-Verlag Berlin Heidelberg 2006." I have used it for modeling the gas kinetics for gasification.
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I think mesh-based methods can be completely replaced by mesh-free methods, but maybe mesh-based methods such as FEMs have some useful properties that mesh-free methods don't have them.
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In general, for similar problems and at the same level of demanded accuracy, FEM is faster than mesh-free methods. The reason is the necessity of seeking the neighbouring nodes at every step, it's extremely time-consuming job.
Nowadays, mesh-free methods (again, in general) should be used only in two cases:
1. When mesh deformation is a significant problem. In such cases mesh-free is faster, or just only available method. For FEM deformation of elements can be overcame by dynamic remeshing, but it's time-consuming too and not always works correctly - than one can use mesh-free method.
2. When many crack surfaces are developed in the material - like for example in crushing a ceramics. For FEM, alternatively one can use XFEM method, but it's slow.
So answering the main question - in the near future, mesh-based methods rather will not be fully replaced by mesh-free methods - they are too slow.
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I am working on an analysis in which oil flows through a tube and causes a turbine to spin. I would like to add friction between the spinning turbine and the shaft as it is spinning around.
Currently, according to CFD, the turbine is spinning at over 7 million RPM at average flow which seems completely impossible. Any insight on this matter would be greatly appreciated.
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Hello Isabelle,
Since I am here on campus, you should feel free to drop by, room 007A Hayden. Something is indeed wrong with your simulation, and it is not just a matter of friction: a turbine even without skin friction or form drag will still have a fixed angular velocity relative to the flow velocity, just like a screw turning through wood... Jim Papadopoulos
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I calculated the flow in arteries and I would like to show that for some time steps the wall shear stress has the opposite direction, for example in the curves, branches, etc. For the straight pipes it is easy but how to do it for the more complicated geometries?
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I think that you should use MATLAB to write a piece of code to control the dynamic mesh.
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I am doing analysis of centrifugal pump in turbine mode. I meshed model in turbine mode. Then exported in Gambit for boundary conditions. Then read mesh file in fluent and done 3 D analysis. After doing complete analysis I closed fluent. When I start fluent again and read cas and data file it shows error of grid interface. It shows like this:
Building...
mesh
Error: %%create-sliding-interface: wta(sb2-id)
Error Object: sb1-id
materials,
interface,
domains,
mixture
zones,
default-interior:014
default-interior:001
default-interior
inlet
outlet
outlet_pipe_wall
casing_walls
wall
interface_1
interface_2
interface_3
interface_4
Skipping zone wall-18 (not referenced by grid).
Skipping zone wall-19 (not referenced by grid).
wall-21
wall-22
casing
impeller
outlet_pipe
interior-17
interior-20
Error: CDR: invalid argument [1]: wrong type [not a pair]
Error Object: #f
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you are doing something wrong when your are defining boundary conditions in the gambit might be your are not able to give proper interface between two interior faces or didn't define flow field very well that the reason this error come so i would like to suggest you to do meshing and give boundary conditions at meshing packages like gridgen, icem  or you can use fluent mesh as well to resolve this issue.
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In CFD for which applications do we take the conservative governing equations and for which applications do we use the non-conservative governing equation?
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We drive the governing equations by considering a finite control volume. This control volume may be fixed in space with the fluid moving through it or the control volume may be moving with the fluid in a sense that same fluid particles are always remain inside the control volume. If the first case is taken then the governing equations will be in conservation form else these will be in nonconservation form.
See the book "Computational Fluid Dynamics - The Basics and Applications" by Jhon D. Anderson
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To better understand the discretization and also to narrow the mesh independent test.
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I assume you are talking about RANS. I think the mesh size mainly depends on the y+ of the first grid point near wall (y+_1). If your mesh is fine enough to make the y+_1 less than 1.0, it means the mesh is fine enough for LES, you reach the maximum size; To make law of the wall (log law) working, you y+_1 has to be less than some value. This value varies for situations, usually less than 5,000. Thus, 1.0 < y+_1 < 5,000 gives you the maximum and minimum mesh size.
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of temperature, the model doesn't seem to handle the heat produced by Joule dissipation. It is going further
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I don't know how high the temperature gets, but at high temperatures heat-loss due to radiation may be a significant contributor to keeping the temperature down. Did you account for this?
I don't know the HMNF module, but you should make sure that it accepts a temperature-dependent electric conductivity.
Hope it helps.
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I have been asked to represent a rectangular shape as a mesh. I am doing a numerical work which deals with flow inside tanks in case the tank subjects to external excitation. The dimension of the tank is considered to have 104 points in x-direction and 60 in y-direction. Does anyone know how can I handle this task?
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I suppose, you mean to mesh the tank so you can do flow simulations. For this, you need to create a checkerboard like pattern. I mean that you create 104 vertical lines and 60 horizontal lines to get mesh of rectangular shape.
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Velocity profile is a factor, that you could find the velocity in any depth of fluid by changing the variable.
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Basically, the profile of velocity not only shows you the magnitude of velocity but also shows you the characteristics of the flow like direction, change due to shape of the domain or increase-decrease in the velocity magnitude with respect to the geometry and so on. So in general, it helps you to understand how the fluid behave while it is transported through the domain.
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I would like to verify my FLUENT model for the dam-break process on a positive slope (upward, like a beach). But my reservoir is in the horizontal plain. Can you suggest some literature for this purpose.
Secondly, can dam-break be modeled with laminar flow conditions (instead of turbulent k-epsilon model)?
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What is the flow properties.
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Fluid mechanics.
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There can also be inertial forces if you are in a non-inertial reference frame.
With ionics liquids, electromagnetics forces can also be added to gravity if external electromagnetic fields are present.
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I am learning to develop algorithm for flooding and drying. And am using the 2D shallow water model.
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Note that the 2D-shallow water model excludes viscous effects; thus it inherently cannot describe the dynamics of dewetting that would lead to dry spots. Further, the shallow water model cannot describe the flow of thin liquid films near a boundary, the dynamics of which are dominated by viscous effects. I think the approach you will have to take is one based on a singular perturbation analysis, in which the outer solution is described by the shallow water wave model and the inner solution ( when the layer thickness is sufficiently thin) described by a lubrication-like flow dominated by viscosity and surface tension. There are many examples in the literature that discuss deweting of thin films using a lubrication model.
But your challenge will be to define the appropriate scalings such that you have the correct limits as the layer becomes vanishingly small in thickness, and have the correct matching conditions.
Perhaps others on the forum know if this has been done before- I am not familiar with the literature of shallow water waves....
Heat Exchangers
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Can anyone tell me what will be the end result if the tube of the tube and fin radiator is increased after certain length?? For ex Case 1: tube dia (D)= 10mm and Tube Length (L)= 100mm case 2: tube dia (D)= 20mm and Tube Length (L)= 100mm case 3: Tube Dia (D1)= 10 mm till 50mm length and then 20mm for remaining length Give explanation on each case pls!!!
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The aim is to model nanometer level contact problems involving fluids, better and in more detail regarding e.g. energy transport and friction.
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When I compile the code (written by Stephane Popinet), I am faced with a code warning like "max residual...". A screenshot is attached.
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Hello,
Gerris uses a prediction-correction method to solve the NS equations. The correction phase requires to solve a Poisson equation to obtain the pressure and a divergence-free velocity field. I think that the problem comes from this part of the computation.
This kind of problem is not supposed to happen if you use the default Gerris cases without modifying them. If you obtain this error with the standard version of the script file, you should contact directly Stéphane Popinet (he is on RG).
If you have modified the script file, please tell us what you have changed and I'll try to help you.
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I have meshed my design model but i am not able to export it to fluent (CFD). Everytime it displays an error in fluent. Please guide me.
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If "mesh exported successfully" message is displayed at bottom of Gambit transcript window, then only one possible mistake would result in displaying an error in Fluent. Either you are reading a 2D mesh in 3D fluent session or 3D mesh in 2D Fluent session.
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Hi,
I have a set of PIV vector data recorded at 5000 Hz (!), representing a flow field around a bluff body. Downstream of the body, the flow seems to be turbulent. I want to find out, if the flow has an impact on small droplets. Therefore i want to calculate the Stokes number St=(Droplet relaxation time)/(Kolmogorov time scale). It is no problem to calculate the droplet relaxation time, but for the Kolmogorov time I need the turbulent energy dissipation (epsilon). Epsilon is difficult to calculate from the PIV data, since spatial and temporal resolution are limited. Today a collegue told me someting about an analogy between the Kolmogorov time scale and a Reynolds time scale (?). He said something about Reynolds time being about six times larger than Kolmogorov time, but I was not able to find his equation in literature.
Has anybody a helpful comment on this topic? Is there a way to approximate the Kolmogorov time scale?
Greetings,
Greg
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We typically use other statistical functions to get the estimate of dissipation, e.g. structure functions, Taylor surrogate, etc. If you're interested in more details or cooperation, welcome off-board to http://www.eng.tau.ac.il/efdl
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Hi... I am modeling open sea air turbulence (Re ~ 6.0e6) using SST (Menter) K-Omega RANS based turbulence model. What should be turbulent intensity (T.I.) at inlet? 1%, 5% or 10%? Also, does anyone have experience on influence of drag prediction for different T.I.? What's the physics correlating T.I. and Drag?
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@ Roza: I guess this formula is true for internal flow (e.g. pipelines, inlet duct). Let me correct if I am wrong.
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Most of the papers I have read say that in the absence of pooling, the boundary condition at ground-level is given by a flux, something like q = K(dh/dz + 1). But I have not found how to specify what q is. It seems to me that it should be related to the humidity, and also the current level of saturation at the soil surface. Is there a common consensus on an elegant way to describe this boundary condition?
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Dirichlet condition (specified pressure head) can be assigned by using thermodynamic relation - please see Equation (12) in my paper at http://www.angelfire.com/nh/cpkumar/publication/IEI_1996_Evaporation.pdf
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I am proficient enough in programming using C and MATLAB but when I open any CFD text book, all i find is calculus. I want to slowly learn writing my own code but the books don't give any idea how to proceed with those hifi mathematical schemes.
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Hi Surya,
A strong or atleast functional understanding of calculus and numerical techniques is required to truly understand the code behind CFD and program a solver. Familiarity with C, C++, Python and MATLAB will definitely help in this direction. The programming codes are written to implement mathematical schemes.
Text Books : You can refer to 'Versteeg and Malalasekara' for a good introduction and specific guidelines/ an example to programming a pressure based algorithm. I also recommend using John Anderson's - Introduction to CFD, which is a great book for the theory with a gradual progression in the complexity of the mathematics involved. Another book that should help relate to the coding is 'Applied CFD - Rainald Lohner'.
A simply worded introduction to CFD , focused on concepts and much less mathematics (and a free ebook) > http://bookboon.com/en/textbooks/energy-environment/computational-fluid-dynamics
To understand Fluid Mechanics on a fast(er) track, try the videos and notes at > http://web.mit.edu/hml/ncfmf.html
Some very nice sources for coding examples : http://storify.com/ShreyasRagavan/software-and-code-related
Once you get along, you might want to plunge into open source CFD applications like OpenFOAM and SU2.
I'd recommend playing around with SU2 before going for openFOAM.
Have a look at the resources I've collated > http://cfdrevolutions.weebly.com/resources.html
The 'open access' and 'mathematics' sections have resources that can help with streamlining your understanding of the required calculus. The links I've posted above are spread across different sections and are available in the website.
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What are the boundary conditions that should be imposed in order to obtain the simplified momentum, energy equations for shock waves? Is it possible?
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What is your problem exactly?
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Software- fluent 12.0
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:) ok I ll check. Thank You Shantanu.
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Are there any published results for experimental data of measurement of skin friction drag of a triangular plate at zero angle of attack?
Also, can we use theories developed for solving boundary layer over a flat plate (like blasius equation) to estimate the skin friction drag over a triangular shaped plate at zero angle of attack?
Thank you in advance!
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You can use Blasius theory if the flow is laminar, but those for the fully turbulent flow von Kármán’s empirical formula has to used.
You can check the calculation by Squire and Winterbottom, "Note on further profile drag calculations.
RAE Rep. BA 1634, 1940.".
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A three-day course in ''Large Eddy Simulation (LES), hybrid LES-RANS, Detached Eddy Simulation (DES) and unsteady RANS'' is given at Chalmers, Gothenburg, Sweden, 27-29 June, 2012.
LES is suitable for bluff-body flows or flows at low Reynolds numbers. To extend LES to cover industrial flows at high Reynolds numbers, new approaches (hybrid LES-RANS, DES, URANS, SAS, PANS) must be used. They are all based on a mix of LES and RANS. The course will give an introduction to LES and these new methods.
LES, or any of the new approaches, is the first step when performing accurate CAA (Computational Aero-Acoustics). Lectures will be given in the mornings; in the afternoons there will be workshops using Matlab on PC Workstations.
In the workshops, the participants will use Matlab for analyzing SGS models, hybrid LES-RANS, SAS and PANS. Matlab scripts will be used to generate synthetic turbulent fluctuations for inlet boundary conditions and embedded LES.
The number of participants is limited to 16. For more information, see and Lars D.
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Thanks
Vikas Sharma
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I think it could be possible using the Lattice Boltzman approach ?
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Sir I want to validate this paper. PDf attached.
I have a Simple Flow Situation If you can give a minute , It will Be Solved and my life will be a lot easier.
I have a 3d duct, with a small obstruction/wing to create disturbance.
, Walls are at 400 k constant temperature.
and air at 0.8 m/s at 300k.
the duct is 21 x 14 X 160 mm.
well they are two parallel plates that are 14 mm apart. and the side are open , which are at 21 mm, i have defined symmetry.
It is similar to tutorial "Forced Convection over a plate""https://confluence.cornell.edu/display/SIMULATION/FLUENT+-+Forced+Convection+over+a+Flat+Plate", except, that , that my problem is in 3 d .
Most of friends have replied me like this " As far as finding nusselt number, that is the only way of doing it. ie. report surface integral and manipulate them in excel and then plot. "
i use h*x/k along a line at the bottom plate in its mid, but that gives the local axial variation i think.
but i need average, without using exel if possible.
Anyone intrested in seeing the *.cas, *.dat, *.lay files can mail me, i will send the files so that one can check properly.
Regards Saksham
+919467704656
any help on Tecplot or Fluent is welcome.
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I suppose you want to solve the Eq. 4 of the paper. Once you've simulated the flow you already have T_w1, T_w2 and T_b values. You can solve the denomiator using any numerical integration algorithm. For the numerator, first you find the heat transfered q_1 and q_2, trough Fourrier's Law. Use some numerical differentiation technique to find dT/dx and then integrate it. I would use MatLab to solve this.
Sory if I wrote something useless, I didn't read the paper neither understand your real question. :)
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Hey there,
I am trying to set up experimental equipment to measure the diffusion coefficient of ATP and ADP in Cellculture Medium. I did some experiments before to measure some other metabolics of cells, but it was done with a self constructed two chamber system. Now i want to go "more professional" as it's for my phd thesis. Does anyone have experience with two chamber diffusion measurements or can give me a hint what kind of system would be the best?
I can set up my self, but right now, the membrane between the chambers is the biggest problem because the diffusion length is not given accurately enough due to not exactly vertical membrane poreways.
Thanks in advance.
Alex
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Can anyone provide an explanation?
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1: export your CAD as IGES format
2: Import that file in meshing tool and mesh there and save the mesh file.
3: now you can run that mesh file in fluent.
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I mean there is any simulatio program or softwear can do it simulatio for bod human or for any part of body?
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You are not very specific as to what exactly you want to simulate- physical motion (kinematics), chemical processes, ergonomics, or any number of other approaches. Perhaps this paper (http://www.cescg.org/CESCG-2000/RFilkorn/) can provide you a starting point.
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For example, there is a strip placed in center of a room, and is a high frequency noise source. Does the code allow to simulate the effect of this noise on the surrounding flow?
Thanks in advance!
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Hi Charles.... thank you very very much for the links. Really helpful.
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I collected raw data from the field and intend to generate a function from the data, how do I do that?
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You might give Eureqa a try. http://creativemachines.cornell.edu/eureqa
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I am interested in solutions of Nonlinear hyperbolic conservation laws with jump conditions (propagation of shock wave).
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The present topic of my study is generalization of Riemann invariant for hyperbolic system based on symmetry analysis. The final goal is to construct a generalized Riemann invariant and its application to CFD. But, I',m not researcher of CFD.
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now days i carried out simulation of flow pst circulare ,square ,triangle cylinders by using fluent
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Please see Karabelas,S.J., et al ,Applied Mathematical modelling,36(1),pp379-398,2012.It is high Re but you just avoid the turbulence model, if you prefer.
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I want to simulate a diesel exhaust system and verify it by measured data of pressure drop. I am so far unable to find any data pressure drop. I am also confused about what properties to consider for diesel with suspended particulate matter.
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Can anyone help me in Computational modeling of Wind Turbine's Wake? I am just not sure to how to start this project in 2D? assuming an actuator disc doesn't always work... any new ideas?
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Wind Turbine wake modelling is not a simple problem and simply selecting one CFD package over another is not the answer.
Modelling the flow over an aerofoil section requires a fine and rather sophisticated mesh to capture the boundary layer separation. This means elements in the 1mm range on the blade surface.
Problem is an wind turbine is massive which means a lot of elements. The second issue is the wake zone, what exactly are you trying to measure or simulate? If it's related to the performance of the blade section then you really don't care what happens downstream because this has no influence on the blade past 1 rotation (turbulence from the proceeding blade due to the solidity factor).
If however you are trying to model the low frequency noise that is driving everyone mad then you need to accurately capture the pressure pulsations.
That is an extremely difficult problem to solve because all of the current CFD commercial packages are highly diffusive due to the dominate face centered solvers.
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Is there anyone that conducted research on supersonic caviyt flow with FLUENT or other CFD codes?
or, is there anyone interested in this topic?
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yes i am interested, presently i am working on fluent.
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Anyone out there with experience coupling syrthes with Code_Saturne? Actually, my issue seems to be getting syrthes set up properly- I have tried building four different versions of the code on two different computers. The executable appears to be made properly, but always winds up with a segmentation fault at exactly the same point in the execution:
**TEMPS D'ENTREE ETAPE DE RESOLUTION DE LA CONDUCTION : 3.680000
Segmentation fault
The results files are built, but empty. The mesh appears OK (it is from an example that others have run), converts to syrthes format, then I can also look at it in Paraview after reconverting to ensight.
But, the program just won't go beyond telling me what my initial temperature is...
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I need help in sector , trimmimg and mapping method of combustion analysis of Diesel engine
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Dear Dr. Sandeep Joseph,
It is better that you ask the your question on STAR-CD online discussion forum in CFD online.
I think you can get more help rather than here.
Regards,
Souichi Murata
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I'm working on elliptic geometry that is made to rotate at a distance from the central axis of the duct. I need to determine the local and average Nusselt number.
The values being generated from FLUENT are too low
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Dear Popolla
I am working on similar kind of problem, In my problem fluid is flowing past an unconfined elliptic cylinder. While calculating the Nusselt Number, I use area weighted average method tool box. second thing is that if you are using very high Prandtl number and Reynolds number, then you should have super fine mesh near the cylinder surface to capture the thin thermal and hydraulic boundary layer.
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I have to simulate a THREE PHASE SEPARATOR in which water+air+chemical enters into the chamber and water is to be taped out from one (01) OUTLET
and Air from second (02) OUTLET and chemical remains in the chamber...
***The problem here is that MIXTURE is set on all boundary conditions as well as on OUTLET. I am unable to select any one (01) fluid at OUTLET using FLUENT.
Can FLUENT Simulate this problem?
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Yes, it will be simulated in CFX not in FLUENT.
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I want to solve a CFD problem with a mesh generated by my own code in OpenFOAM. The question is: in what format is better to export the mesh for OpenFOAM?
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Thank you Bruce, the problem I have is that writing the point file is not difficult, quite intuitive actually, but the others, since they require the knowledge of the relationship between an element and the other, are a bit difficult. Anyway, thanks a lot!
Cheers
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I need to generate a mesh over the surface of a 3d object consisting of a number of intersecting cylinders. This needs to be done repeatedly, within the loop of an optimization. I'm hoping there is a simple and free tool out there that could handle the task, so I wouldn't have to make my own. (Panelizing the cylinders is easy, but making an algorithm to deal with panelizing the intersections would be too complicated to code myself.) Are there any such software tools out there? Ideally something that could be called from within matlab or a c++ code?
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There are a couple of free tools available, for example gmsh (take a search machine to find). However, I suppose you additionally need something with open sources to add your routines for automatic processing. This is not always the case with otherwise free tools. A good start to search for a suitable instrument is:
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Total drag is sum of viscous and pressure drag . code Cdp and Cdf in C++??
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Hi Krunal,
You just need to integrate the total stress tensor on the surface of your immersed object. Have a look at: international Journal of Multiphase Flow. 04/2012; 40:38-55,
There are some suggestion for the interpolation and integration of the stress tensor on the surface in the context of fixed mesh methods if using a body conformal mesh the problem would be much simpler. Of course there is no code in the paper but should be pretty straightforward to implement the method in any Languages.
Not sure what you mean by FDM (finite difference method maybe?) but I think the important thing is the type of mesh you are using and you need some interpolation and integration to calculate the surface forces.
good luck
Sina
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I'm not very clear about the no-through condition and no-slip condition. When I write programs to do the impulsively started cylinder simulation, I found that after convect the particles, a few enter the boundary. I want to know whether the no-through condition should take into account this time and how to do it.
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What is the "no-through condition"? A replacement of "solid boundary", i.e. "wall"?
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Original fluid composition, composition of any swelling test fluid. Any suggestions?
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How can we raise the limits of integration for a triangular element in cylindrical coordinates in FEA? How are the limits in the radial and tangential direction?
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I have to discretize a spatial domain through triangular elements but shape functions must be expressed in terms of cylindrical coordinates, i.e, radial and tangential coordinate. The problem arises when I perform the Galerkin integral because I have to know the limits of integration for each coordinate in element but I don´t know how to raise it.
My problem is solve a motion equation in a vortex.
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I am using the SSME geometry to perform a CFD analysis for the flow characteristics, thrust and plume. I am using an Inviscid density based solver with 20 MPa and 3500 K for my inlet. I am having difficulties in defining the pressure and temperature at the exit. Also should I be using a different type of solver (i.e. Pressure based SA Modle, etc.)?
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Sorry, may I know the SSME geometry. Usually we are doing cfd analysis for control volume. if we define inlet boundary conditions, then cfd gives output values for control volume.
who can send “Parametric study of a vortex diode for a nuclear reactor emergency shut-off system” paper to me?
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I want to read this paper.
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sorry to hear that. I see now it's a thesis... maybe you can ask it directly to the author!
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I am a Student of M Tech (CFD) and working on Nasal Airflow simulation. I want to prepare a 3D geometric reconstruction of Nasal cavity. The computer tomographic (CT) images are used to obtain 3D model, but I dont know how ? Can anybody help me by explaining how these images are processed to get 3D model and is there any software used in medical technology to convert into 3D model ?
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Hi,
I think I have an answer for you! 3D animation program Blender can help you to prepare the nasal cavity, the air and the simulation of it. It is a free software which is worth thousands of dollars.
Check the links in the following order:
Good luck!
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1. When the liquid content between grains is small, liquid bridges are formed at the contact points of grains and create the meniscus models.
But I can't imagine where the liquid bridges would be generated when the liquid would flow into the grains. Which grains will be included? That is to say,
How is the connection between the grains generated? Is there a theoretical basis to explain this phenomenon?
2. When the liquid content between grains is small: how to calculate the liquid bridge force accurately?
When the liquid content between grains is more or almost saturated, how to calculate the suction due to the pressure difference between the air and the liquid?
Some references to explain this phenomenon would be very helpful.
3. We know that the wet granular materials can express complex phenomena, such as the repose angle can be larger than 90 degree.
But I wonder that whether cohesion is enough to express this phenomenon? Or should we take the lubrication of solid-solid friction caused by liquid into consideration?
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Hi Sheng,
I think you have some questions the answers for which are still on-going research. however in-regard to your second and third question I would suggest you to read the following article especially the first 3-4 sections of the paper. You can get a better idea about liquid bridge formation, forces, cohesion, lubrication(little bit) and references to article on angle of repose.
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I am trying to simulate BL transition on a flat plate at 50.1 m/s and 0.18% Tu. The plate is 1.8 mts long. Although, I detect transition on the plate it is way too early and is not correlating with the paper whose simulation I am trying to repeat. This is extremely strange because I have followed their instruction and have set the mesh parameters right with a y+ of 0.1. (I have mirrored the authors mesh). The only difference is they are using the SST gamma-theta model in STAR CCM and I am doing it in FLUENT.
Does anyone have any suggestion on how to improve the simulation? I am attaching the reference paper. Please see figure 3 in the attached paper and Case 1-TSK.
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Are you certain that the turbulence is "created" at your inlet boundary condition?
For some turbulence models, such as the SST, you have to provide values of turbulence properties at the boundaries. For your turbulence closure, you should provide to the code values of the "k" and "w", and maybe other, properties depending on which solver you are using.
I hope it was useful,
Good luck!
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I am using k-epsilon model , is there a fluent tutorial available
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Did you try looking at the static mixer tutorial in fluent?
Try googling it. It should be easy to find.
Hope it helps.
Best wishes...
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Idea of learning a analysis software.. Which among the four is best with respect to application, popularity, useage and user friendly? I learnt Ansys structural and thermal analysis but yet to learn Fluid Analysis... Hyperworks is mainly for meshing but anyway I include it too... Please suggest me with better options..
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First learn the concept with any one of that , than you can choose . Because diferent people woring with their requirment.
Thanking you
Best regards
SUJAN
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Materials that can be useful.
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I need to simulate wet&dry cyle of concrete cylinder by real test results.
My question is in ANSYS since I do not know how to model moisture transport analysis. Mainly I have difficulties in running coupled moisture transport and heat transfer. Do you any training reference or input files ?
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Micropolar fluid
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Do you think that i can simulate that with comsol?
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I have modeled the arc chamber.
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DO you want to run thermal simulations or design simulations for your model. For thermal simuation use FLUENT.
btw in which software did you model your "arc chamber".
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I am solving lid driven cavity using fvm and am having issues regarding scaling the residuals.
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it depends on the problem. for unsteady terms like du/dt you must put all the d/dt<0.001, and for pressure equation you can employ ((Pnew- Pold)/Pnew)<1e-8. if you want to get most accurate results, the following conditions are suggested
1. d/dt<0.001
2. ((Pnew- Pold)/Pnew)<1e-8
3. ((Unew- Uold)/Unew)<1e-8
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I want solve by shooing method but I am not getting it. We can also use F''(-infinty) =0;
and F''(+infinity) =0; can anyone help?
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As I am sure you know, this is the Blasius equation. Below is a shooting method that I once wrote in matlab, for the typical case where you shoot from y=0 to infinity in order to get the ZPG boundary layer profile. It will be easy to adapt to your case.
Shooting from minus infinity to plus infinity sounds like a bad idea for stability issues - I suggest you shoot from y=0 in both directions, and you adapt the (unspecified but needed) BC for F'(0) iteratively.
To try this routine, pick a y0 not too far from 0.33:
======================
function [T,Ynew]=shootingBlasius(y0)
% by Lutz Lesshafft, 2011
% solves the ODE y''' + y*y'' = 0 with BC y(0)=0, y'(0)=0, y'(inf)=1.
% input parameter y0 is initial guess for y''(0).
% shooting algorithm:
[T,Y0] = ode45(@diffeqn,[0 20],[0 0 y0]);
y1=y0+0.01;
[T,Ynew] = ode45(@diffeqn,[0 20],[0 0 y1]);
while (abs(Ynew(end,2)-1) > 1e-15)
ynew=interp1([Y0(end,2) Ynew(end,2)],[y0 y1],1,'linear','extrap');
y0=y1; Y0=Ynew; y1=ynew;
[T,Ynew] = ode45(@diffeqn,[0 20],[0 0 ynew]);
disp(ynew);
disp([' error: ',num2str(abs(Ynew(end,2)-1))]);
end
end
function dy=diffeqn(t,y)
dy = zeros(3,1);
dy(1)=y(2);
dy(2)=y(3);
dy(3)=-0.5*y(1)*y(3);
end
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Does anyone know how to time-average NO mass fraction in FLUENT?
After running combustion transient simulation, I enabled NOx model and turned off all equations except NO. Then, I continued the iteration.
However, NO mass fraction, concentration and rate of production being calculated appeared in the data sampling statistics. So, I could not get their time-averaged values.
Please kindly give me some suggestions.
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Calculate time averges outside of Fluent by writing the value to be averaged at each time step in the computation. The writing can be done using monitors where you can form various quantities from the solution and instruct these to be written to a file. That file will have time and the quantities written so can be read into a program such as Matlab or Excel to calculate the required average.
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If we want to simulate long period case, we must use time scale to reduce our simulation time. But, I still dont understand the effect of NS Equation. How is the effects?
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Scaling through non dimensionalization makes your max time as 1. When we non dimensionalize NS equation, we non dimensionalize other parameters like velocity, viscosity , pressure as well. But as we scale, our time step decreases, hence there is no effect on final solution for NS in simulation.
Hope this helps.
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I am writing a cfd code for solving N-S equation on a structured collocated grid (lid- driven cavity), my code is slow because of the above reason.
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You must check the error control subroutine. Probably the error target is very small, and mathematical or phisical oscillation makes that the code runs even in the stady state.
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What are the physical quantities that are examples of a surface source term in a general integral conservation eqn and why is it a tensor?
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Is it possible to simulate fire using Fluent in CFD?
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It was once done in COMSOL. Please read the abstract :
"Analysis of burning candles is extremely complex; combustion produces a highly non-linear temperature profile through the flame in which local temperatures may exceed 1400 °C. Heat transfer includes radiation, conduction and convection components and the low melting point of the candle wax leads to a phase change that allows mass transport via capillary flow prior to combustion in the flame. COMSOL Multiphysics has been combined with generalized strategies to analyze heat transfer and fluid flow during candle burning. Radiation was included through a radiating surface that was non-locally coupled to the radiating gas volume. The dynamic behavior of the plume was incorporated by artificial diffusion to give a time-averaged approximation. Heat transfer within the liquid wax used an anisotropic thermal conductivity to account for convection in the horizontal direction. The analyses predict the velocity flow field for a half-burned three-wick candle and demonstrate spreading of the flow away from the flame. Predicted temperature distributions in the wax and candle container compare favorably with experimental measurements"
Sloshing experimental work is needed!!
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Hi guys, I have been searching for this thesis " NUMERICAL AND EXPERIMENTAL INVESTIGATIONS OF CAPTURING LIQUID FREE SURFACE FLOW PROPERTIES IN SLOSHED TANKS" but I was not able to get it. I even contacted the author and he did not respond for my email. Why this thesis is important to me? well because I am doing a numerical work that simulate the sloshing within the Tuned Liquid Dampers (TLD) and this work contains experimental part that I would like to make my simulation based on. If anyone knows how to get it or any other thesis that contains the experimental work of a fluid sloshes within rectangular tank under a harmonic excitation force, and it is important to include a figures of the sloshing force time history and/or the free surface evolution so I can compare my numerical results with them. I would be more than appreciative for any help. Thanks once again.