Science topic

# CFD Coding - Science topic

This topic is to discuss the various issues involved in debugging or writing any kind of code in cfd .

Questions related to CFD Coding

Dear all,

I have tried to simulate the phase change from a solid to liquid in Ansys FLUENT by providing heat flux at a wall [Using the Solidification and Melting model]. I got the results [video attached: 0-1 min temp plot, after 1 min liquid phase plot]; the heat flux creates temperature change over time, leading to a change in phase based on the solidus and liquidus temperatures.

But, the fluid flow doesn't occur, i.e., the flow equation is not solved. I want to simulate the flow of liquid PCM due to gravity. Is there any predefined option to perform that? or is any udf available? Kindly help me..

Hi, I have been trying to import the thermophysical properties of CO2 (for the supercritical region) to Fluent by using UDF. End of the analysis, the result is not correct. I think Fluent is pulling a Tref value which causes my enthalpy to go negative; therefore, the energy equation does not give accurate temperature results, so the result of thermophysical properties, which are functions of temperature, are wrong. I want to be grateful if you could share your recommendations, especially on the methods of correct calculation of enthalpy. My specific heat code is as follows:

#include "udf.h"

DEFINE_SPECIFIC_HEAT(supercritical_cp, T, Tref, h, yi)

{

real cp;

if (300. >= T)

{

cp = 2.256999118844760E-02 * pow(T, 4.) - 2.606618818487370E+01 * pow(T, 3.) + 1.129129898467780E+04 * pow(T, 2.) - 2.174235523392760E+06 * T + 1.570278261279480E+08;

}

if (300. > T >= 306.)

{

cp = 1.147018354719330E+01 * pow(T, 4.) - 1.385519872072390E+04 * pow(T, 3.) + 6.276090044658930E+06 * pow(T, 2.) - 1.263530241490370E+09 * T + 9.539285116131690E+10;

}

if (306. > T >= 307.8)

{

cp = -1.611612838918710E+04 * pow(T, 4.) + 1.978085636985280E+07 * pow(T, 3.) - 9.104578256081260E+09 * pow(T, 2.) + 1.862478067464320E+12 * T - 1.428738938943020E+14;

}

if (307.8 > T >= 310.)

{

cp = -1.576135476848110E+03 * pow(T, 4.) + 1.945866130859760E+06 * pow(T, 3.) - 9.008641337104630E+08 * pow(T, 2.) + 1.853611584329810E+11 * T - 1.430227164258690E+13;

}

if (310. > T >= 320.)

{

cp = 1.770529718817220E+00 * pow(T, 4.) - 2.242833202341920E+03 * pow(T, 3.) + 1.065432793165650E+06 * pow(T, 2.) - 2.249454519629040E+08 * T + 1.781003821884030E+10;

}

if (320. > T)

{

cp = 2.086961941877520E-03 * pow(T, 4.) - 2.851496372954040E+00 * pow(T, 3.) + 1.461548345109060E+03 * pow(T, 2.) - 3.330816449664890E+05 * T + 2.848088978782360E+07;

}

*h = cp*(T-Tref);

return cp;

}

I am trying to use NIST Real Gas Model for heat transfer studies of super-critical water. I want to write a code to be used in fluent and know nothing about coding. Will some one please help me as it is a part of my final year project.

Thanks in advance. :)

I have a specific case about internal pipe flow with constant heat flux. Although the inlet boundary condition is laminar, the flow is a passing transition (a significant part of the tube) and turbulent regime along the tube (because of the change of thermophysical properties depending on implied heat). SST models with intermittency term (For fully laminar flow, γ = 0 and the model reverts to a laminar solver. When γ = 1, the flow is fully turbulent.) can catch laminar/transitional and turbulent flow regimes. These models were designed for turbulent inlet boundary conditions (models solve intermittency term, so it needs extra boundary conditions such as turbulent intensity). Can Transitional SST Models be used for laminar inlet / turbulent outlet boundary conditions? If so, what is the approach?

Regards,

EB

Dear researchers,

I am currently working on the development of a Low Mach Number multi-species solver (a system similar to that used in LMN combustion, but with no reactions at present ...) I am having issues with deriving the exact temperature equation (note that c_p varies for each species...) I emphasize that I am looking for having an equation expressed as a function of the temperature (not enthalpy, not internal nor total energy !)

- Can you please help by providing some references that can help to derive this equation ?

- Shall I start from the conservation equation of the internal or total energy ? should I neglect specific terms ?

- From your experience, is the inter-species diffusion term important and should be taken into account in such a system of GE ?

- Same for the term div(Pu) ? any ideas

- Same for the viscous tensor (u Tau) ... this is so complex to code in fact ....

Thanks for your comments and recommendations !

Regards

Elie

Hello,

I've successfully simulated the closure of a flapper non-return valve as illustrated.

The inlet velocity increases gradually with a specific acceleration.

The following UDF is used to specify the motion of the flapper:

#include "udf.h"

DEFINE_SDOF_PROPERTIES(flappers_motion, sdof_prop, dt, time, dtime)

{

Six_DOF_Object *sdof_obj = NULL;

sdof_prop[SDOF_MASS] = 2.73e-3; /* flapper's submerged weight */

sdof_prop[SDOF_IXX] = 2161.86e-9; /* around the hinge */

sdof_prop[SDOF_IYY] = 367.96e-9;

sdof_prop[SDOF_IZZ] = 2471.27e-9;

real m= sdof_prop[SDOF_MASS];

real L= 0.024479 ;

sdof_prop[SDOF_LOAD_M_X] = 0 ;

sdof_prop[SDOF_LOAD_M_Y] = 0.0;

sdof_prop[SDOF_LOAD_M_Z] = 0.0;

real th_deg = theta * 180 * 7 / 22 ; /* valve opening angle, in degree */

sdof_obj = Get_SDOF_Object(DT_PU_NAME(dt));

if (NULLP(sdof_obj))

{

/* Allocate_SDOF_Object must be called with the same name as the udf */

sdof_obj = Allocate_SDOF_Object(DT_PU_NAME(dt));

SDOFO_1DOF_R_P(sdof_obj) = TRUE; /*1DOF rotation*/

SDOFO_DIR(sdof_obj)[0] = 1.0;

SDOFO_DIR(sdof_obj)[1] = 0.0;

SDOFO_DIR(sdof_obj)[2] = 0.0;

SDOFO_CENTER_ROT(sdof_obj)[0] = 0.0;

SDOFO_CENTER_ROT(sdof_obj)[1] = 0.0;

SDOFO_CENTER_ROT(sdof_obj)[2] = 0.0;

SDOFO_CONS_P(sdof_obj) = TRUE; /* constrained motion */

if (SDOFO_CONS_P(sdof_obj))

{

SDOFO_LOC(sdof_obj) = 0.0;

SDOFO_MIN(sdof_obj) = -0.0349 ; /* min allowable angle */

SDOFO_MAX(sdof_obj) = 1.0471 ; /* max allowable angle */

SDOFO_INIT(sdof_obj) = SDOFO_LOC(sdof_obj);

SDOFO_LOC_N(sdof_obj) = SDOFO_LOC(sdof_obj);

}

}

}

But now I want to simulate the closure of the flapper, taking into account the friction at the flapper's hinge.

I tried to just assign the friction value to "sdof_prop[SDOF_LOAD_M_X]" ,but the flapper started to move backwards (opening) until the flow increases, which is not correct.

So I want to get the value of the hydrodynamic torque of the flapper, and compare it to the friction with some kind of "if statement" that may look like this:

real static_friction= 50;

real kinetic_friction=40;

real hydraulic_torque =??? ;

If (hydraulic_torque<static_friction)

{

sdof_prop[SDOF_LOAD_M_X]=0

}

else

{

sdof_prop[SDOF_LOAD_M_X]=-1*kinetic_friction;

}

BUT THE PROBLEM IS :

I don't know the udf code that can get the actual value of the hydraulic_torque on the flapper to compare it to the friction value.

Your help is highly appreciated.

Thanks a lot in advance.

In order to represent our observations or sight of a physical process and to further investigate it by conducting experiments or Numerically models? What are basics one need to focus ? Technically, how one should think? First, thing is understanding, you should be there! If we are modeling a flow we have to be the flow, if representing a let's say a ball, you have to be the ball! To better understand it! What are others?

Hello all,

I am looking for a simple test case to validate model for perfect gas with heating, preferable flow in a channel. Does there exist any analytical or reference solution for such case

Any appropriate reference would be really helpful. (I am operating in laminar regime )

Thanks

Hello,

I am looking to write an UDF code for inlet velocity!

How can I assign

**inlet transiant velocity**through UDF(user defined function) ? What formula/expression/equation for velocity has to be used for an airfoil simulation? Could you direct me towards - how can this be done in UDF!Your help is much appreciated.

Thanks.

PLEASE I am trying to add a lag to this code after each period. Does any one have an idea how to do that?

"#include "udf.h"

DEFINE_PROFILE(unsteady_velocity, thread, position)

{ face_t f; real t = CURRENT_TIME;

begin_f_loop(f, thread)

{ F_PROFILE(f, thread, position) =A*sin(w*t);

} end_f_loop(f, thread) }"

Basically, I want the loop to initially run for "X" seconds, stop and then start again at "Y" seconds instead of it running continuously as default.

I would like to start a discussion of this specific topic.

Here I would like to discuss the list of possible techniques helpful for performing the simulation of oscillating bodies in quiescent fluid.

This discussion is open to all the students, teachers, and researchers.

I request you to reply here if you are familiar with code development in OpenFoam, IBPM, NEEK1000, lilypad and CFX

I guess my question is quite simple: you know how for compressible CFD codes we have the Sod Shock tube problem that we can use as a benchmark. What if I now want to expand my code and add chemical reactions to it, what would be a good/similar test problem that I could use to validate how well my code runs?

I have a structured vtk file. I would like to convert this to OpenFOAM format in the quickest possible manner. There is a vtkToFoam code library - that is available - however, that is only for unstructured VTK data.

Hello everyone

I have a question can we use an ion exchange membrane for peptide separation from animal blood or plants for example alfalfa plant? if yes then how it will works, I mean how peptide will divide into ions? will amino acid will convert into amino and carboxylic ions?

I read few papers on it but didn't find any helpful paper on it, which give me detail information of peptide separation by ion exchange membrane.

thank you

Irfan Ali

We adopted the famous open source CFD code, openFoam, and the finite element software code_aster in some applications of cardiovascular biomechanics, but havn't using them together to solve fluid-structure interations problems in this field. So we wonder whether they can be used together for solving FSI problem? and if yes, how?

Hello;

I am currently working on a UDFusing the DEFINE_HET_RXN_RATE for Heterogeneous reactions. My idea is to use VOF to describe a simple method of VLE using the vapor pressure of condensable components (in my case water and methanol). I am using the Evaporation-Condensation UDF provided by Ansys in their manual UDF book as a baseline.

By now, I am having trouble with filtering the rate of the reaction based on their names. I was trying to use STREQ and !strcmp command, but every time I compile it gave me the following message:

- error: member reference base type 'real' (aka 'double') is not a structure or union

Besides a problem with an exponent where its values depend on the temperature, it is the only problem I have so I can test the UDF.

I have a question on Cp in the wind turbine. I have calculated the moment in the z-axis as my rotor also rotors along the z-axis. I got the moment values from my simulation. I applied the procedure which ansys recommended formula (P= torque x rotational velocity) for extracting power from the turbine. I got huge discrepancies between actual and theoretical. After calculating power, I have calculated Cp it comes around 0.8 to 1, but the Betz limit is 0.59. plz help me to calculate the Cp.

Conditions :

Turbine Aera =17.5 m2

R=3.5m

V=3

omega=2.14 rad/s

TSR=2

Fluid water (990 is the density)

Hello,

I have been trying to model evaporation at temperatures far well below 100C in Fluent. This is primarily driven by the vapor content of air at the water-air interface.

A saturation temperature UDF is attached below.

The setup this is used with has 2 phases, one a species mixture of air and water vapor and the other is water.

After some help from the forum, I have got it up and running and it seems to be performing fairly well in transient simulations. However, when I try to use this code to calculate the saturation temperature for any steady-state simulation, I get a floating-point error. This is sometimes instant and sometimes after a few iterations. An example error message is:

**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

Stabilizing pressure correction to enhance linear solver robustness.

Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction Stabilizing temperature to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: pressure correction

**Error**at host: floating point exception

I can't understand why I am running into this issue. Is there anything I could try to remedy the problem? I have tested on many geometries, with a variety of problems. Is this UDF unsuitable for steady simulations? and if that's the case then what alternatives do I have? I really need this functionality.

I thought it may be because the system varies a lot so I set up a closed system with a little water in with the walls set to a temperature of 300k and initialized it at 300k. My logic was that the only thing left to solve was the vapor fraction. I got a simulation to run 10000 iterations. However, the vapor fraction was 1.0 everywhere in the gas phase leading to relative humidities many times larger than 100%. This makes me worry there is something wrong with the UDF itself. I know that this kind of study must be possible somehow as I have read papers of people doing similar things, yet these don't go into enough detail for me to successfully imitate.

Any help is appreciated.

Cheers

**#include "udf.h"**

**#define MOLAR_MASS_WATER 18.01534**

*//g/mol***#define MOLAR_MASS_AIR 28.97**

*// g/mol***#define RHO_WV 0.5542**

*// kg/m3***#define RHO_AIR 1.225**

*// kg/m3***DEFINE_PROPERTY(saturation_temp, c, t)**

**{**

*// t: mixture thread*

*// c: cell variable*

*// Cell volume***real vol = C_VOLUME(c, t);**

**Thread *pt = THREAD_SUB_THREAD(t, 0);**

*// Primary phase thread***Thread *st = THREAD_SUB_THREAD(t, 1);**

*// Secondary phase thread*

*// Get the volume fraction of both phases***real vf_s = C_VOF(c, st);**

**real vf_p = 1 - vf_s;**

*// Get the pressure of the mixture***real p_mix = C_P(c, t);**

*// Get the operating pressure***real p_op = RP_Get_Real("operating-pressure");**

*// Primary phase density***real rho_p = C_R(c, pt);**

*// Get mass fractions in primary phase***real mf[2];**

*// Array to store mass fractions***Material *m = THREAD_MATERIAL(pt);**

**Material *sp = NULL;**

**int i;**

*// Species index - 0 for water vapor and 1 for air***mixture_species_loop(m, sp, i)**

**{ mf[i] = C_YI(c, pt, i);**

**}**

**real p_w;**

*// h20 pressure for cell*

*// If secondary phase only***if (vf_s == 1)**

**{**

**p_w = p_mix + p_op;**

*//****** I'm not sure if this is right **********}**

*// If primary phase or mixture of phases***else**

**{**

*// Find the partial pressure of water vapour*

*// partial pressure = cell pressure * water mole fraction*

*// mass of primary phase in cell***real m_prim = rho_p * vol * vf_p;**

*// mass of water vapour and air in cell***real m_wv = mf[0] * m_prim;**

**real m_air = m_prim - m_wv;**

*// No of moles in water vapour and air***real N_wv = m_wv / MOLAR_MASS_WATER;**

**real N_air = m_air / MOLAR_MASS_AIR;**

**real N_total = N_wv + N_air;**

*// water vapour partial pressure***p_w = (C_P(c, t)+ p_op)* (N_wv / N_total);**

**}**

*// Calculate saturation temperature***real t_sat;**

**t_sat = (1730.63 / (10.196 - log10(p_w))) + 39.724;**

**return t_sat;**

**}**

Hello, we have a CFD code written in MATLAB and we wanna save the calculations at a specific node to a text file like ANSYS FLUENT..Any suggestions please?

We will be extremely grateful!

Thank you!

My goal is to study the pressure drop in the tube for different combination of number of fins, fin height and fin width. The internal fins have a certain helix angle and there are a number of fins. The tube has one inlet and one outlet. Since the fins are arranged in a helical pattern, a single helical strip of one helix pitch length is to be modeled. I can understand that a transnational periodic boundary condition can be applied between the inlet and outlet of one strip of the fin, but I am not sure as to how would the sides of the fin can be modeled. I have one reference where he applies rotational periodicity to the sides of that one single strip.I went ahead with the reference, but I got absolutely wrong results. The pressure drop was of the -10^4 order,which is not even close to the reference measurements. The residuals were close to 10^-6 for all the equations.I am using 4 meshed-domains ;2 for connecting inlet and outlet and 2 for connecting the side faces of the helical strip. I applied the periodic conditions through "Mesh--> modify zones--> make periodic" through TUI option in Fluent,however I got a bit confused when a started to input the "mass flow rate" in periodic operating conditions.There was only periodic operating conditions input, so for which PBC I was entering the mass flow rate-rotation and translational ? The model being used is RANS SST k-omega. I also went through the "periodic repeats " option thinking that I have two periodic zones adjacent to each other, but it's usage was for something completely different. Also,since I have gone into a considerable detail, I also want to know whether it's possible to have mixed type boundary conditions ,for example, can I have translational and rotational boundary conditions on two faces of an hellical geometry, such as this pipe?

I need to measure the water depth in the cylinder ( the picture attach) that mixes with air in Ansys CFX, and I don't find an excellent expression to do that.

I'm using Ansys Fluent software for CFD simulation and I'm gonna to learn CFD coding and optimization and also UDF.

Thank you;

Dear all,

In my simualtion domain, I need to use mixture of gas ( N2 gas with 20% CO2) at INLET in ANSYS Fluent.

Mixture model, and species model, may be these models work. Actually,

**I need your support to notify the model and how to put the above specifications on that model too.**Regards

Hi there. Im writing a program in C to solve the viscous burgers equation in 1D using the finite volume method. I am currently using a structured uniform cartesian grid as my computational grid. However i want to implement adaptive mesh refinement in my program. Could anyone tell me the steps i should take in order to do this. Would i have to make i have to make an additional function like say Adapt_Mesh() as well as my Init_Mesh() function and call the Adapt_Mesh() function in the main time loop every time the mesh needs refinement and how could i go about determining if my mesh needs refinement or how would i go about this. Im relatively new to the realm of CFD hence im struggling a lot by thinking how to go implementing this. Could anyone help me. Id be willing to share my current code if anyone could point me in the right direction in regards with how to get started.

*EDIT: Also i have a current gird with 100 cells. If was to adapt the mesh would it refine the mesh so that NX is always 100 ie. by making areas of less density and areas of higher density so that the total points add up to 100 or does the adaptive mesh increase the number of total cells everytime the mesh is refined. This is something im unsure of.

If anyone is curiosus i have attached my program below just incase anyone wanted to take a look

I have a case, which is about internal flow with constant heat flux. Although the inlet boundary condition is laminar, the flow is passing transition and turbulent regime along the tube. As known, the intermittency term is 1 (so, admitted as turbulent inlet BC) for freestream velocity for external flow, I would like to learn that whether using the transitional SST model by laminar inlet boundary condition in the pipe is the corrects way or not.

Best regards,

hi

I am working on the validation of the case which is "simulation of the flow around a circular cylinder at Re=3900 by using XFLOW software " .my boundary conditions is shown in the attached pic. the top and bottom and span wise sides have "periodicity" boundary condition.

my problem is about lift coefficient. my drag is matching with experimental data but my lift isn't. actually lift coefficient in compare with my drag coefficient changes more with decreasing mesh size and become far from experimental data with decreasing mesh size. why does lift coefficient change in this way?

are my boundary conditions true or not?

another thing i want to know is how must be the shape of drag coefficient- time graph at 3900 Reynolds? does any one have a pic or reference?

Thanks for your answers

Farshad Chegeni

I am trying to simulate a heterogeneous reaction between two phases in Eulerian multiphase model. I have written a UDF and it compiles and runs well. The reaction is: C+2H2--> CH4. Although my solution shows reasonable values for reactions rates, but I do not see any changes in Hydrogen concentration from the inlet gas. Can anyone where the problem is arising from?

In the CFD area, it is common sense to set interfaces between two bodies that have different meshes. My questions are:

1) Which set of variables are mapped between two different meshes on the interface? For example, Velocity? Or Massflow?

2) How the solver solves the fields between the interface? Are the fields in the two bodies (on the two sides of the interface) solved together or separately?

Thanks in advance.

Hello everyone, hope all is good.

I want to analyse multi-phase fluid flow through pipe, which software is best to do so ?

Hello,

As part of simulation of gases mixture and water, I need to calculate viscosity of the fluid components and I am using relationships proposed by Chung et al. (1988).

The irony is while I am able to validate that I have coded the relationships well for gases like methane, oxygen but when I am trying to do with water, there is drastic difference, especially for T between 300 K and 700 K.

In order to check if it is only in my case, I was able to find an article where the authors are closer than NIST/CoolProp data base.

I also need to evaluate conductivity and I have same issues for water. In the temperature range mentioned, the conductivity even goes negative in some regions.

I am not able to understand how come it shows this anomaly only in case of water.

May some one help in this regard.

Thanks

(P.S: I can share more info if required. Thanks)

I am developing a solver to simulate compression of oil in shock absorber filled with viscoelastic compressible oil. The model will consider the loss due to viscosity which will decide the response of damper to the shock it experiences. Please include any link or document you think curucial for this.

I have made models for incompressible flows but I am having a hard time to find resources for this case.

Thank You!

Since Abaqus CFD is no longer available in newer versions what are other available codes for Fluid-Structure Interaction Simulation

OpenFOAM is a great open-source CFD code offering impressive accuracy and robustness for free, however, for CFD users who are interested to switch from expensive commercial software like CFX, Fluent, Comsol, etc, it has a steep learning curve, and also it is time-consuming for big projects. To bypass this limitation, Simscale and Simfow have developed a graphical user interface with OpenFOAM CFD code at its core, but you have to pay a license fee. I am interested to know if there is any open-source graphical user interface for OpenFOAM.

Assuming two-dimensional flow, I'm trying to implement a code for a quasi DNS problem. There is no doubt that i should replace the velocities in Navier-Stokes equation (NSE) with its equivalent velocities in the form of u=u_base + uf, where u_base is the steady state solution for NSE for the channel flow and uf is the perturbed velocity which varies with time. By the new definition of the velocities, one can get new extra terms in NSE, as a function of u_base and uf. My point is to find the fluctuation behavior with time so that i can calculate the growth rate and start an instability study for the flow field.

There are two forms of the new NSE, maybe more but at least these two were the common equations which i found in most of the researches which i read. The first one is in the form of du/dt + div(uu) = - dp/dx+ iv(grad(u))/Re where u was defined earlier. The second form is: du/dt + div(uu) = - dp/dx+ div(grad(u))/Re - omega x u.

Which one should i use for the purpose of instability studies?

Note: You can check the attached files for the non-conservative form of the two previous models.

Dear all,

I want to simulate the distribution of relative humidity inside an agricultural greenhouse. I have modelled the relative humidity in fluent using the Species model. the model works perfectly, but when I display the relative humidity contours, sometimes it exceeds 100% !!!

I know that is normal because Fluent uses a mathematical formula to calculate the RH.

but what I want now is to ask if i can write an udf to modify the results of relative humidity as follows:

if RH > 100 ----> Rh = 100??? or does anyone have another solution!!!

I'd be appreciated for any help.

Hi all,

I am modeling a batch reactor which is a cubicle box with micrometer dimension. Inside this box there is a liquid water along with a specis A which is getting converted into B through heterogeneous reaction. B is a solid phase. So i am using multiphase eulerian model. initially there is no phase B. After sometime there will be specis B in the system.

**But what i see is that total mass is increasing with time in the system. why is this happening?**

**Can anyone please help me out?**

**Waiting for your reply.**

Thanks

Vivek

I have mostly come across second-order spatial and temporal accuracy using projection/fractional step method. The spatial derivatives are descritized using second-order approximations. For the temporal accuracy, Kim and Moin use Adams-Bashforth for the convective term and Crank-Nicolson for the viscous terms. However, second order accuracy may be insufficient when one deals with transition or DNS studies. To extend to higher-order accuracy in time, what are the possible schemes, one can use? Can I use WENO (5th order) for space, RK-4 for time? What happens to the poisson equation? Do I need to discretize the second derivatives of pressure using higher-order approximations of Taylor series, instead of the conventional second-order approximation? Any ideas you have may be helpful. Thanks in advance.

Hello all,

I am looking for an method / algorithm/ or logic which can help to figure out numerically whether the function is differentiable at a given point.

To give a more clear perspective, let's say while solving a fluid flow problem using CFD, I obtain some scalar field along some line with graph similar to y = |x|, ( assume x axis to be the line along which scalar field is drawn and origin is grid point, say P)

So I know that at grid point P, the function is not differentiable. But how can I check it using numeric. I thought of using directional derivative but couldn't get along which direction to compare ( the line given in example is just for explaining).

Ideally when surrounded by 8 grid points , i may be differentiable along certain direction and may not be along other. Any suggestions?

Thanks

Many comercial and free code provides some options for modeling non-Newtonian flows.

Which one is very simple to use and appropriate for sludge flow?

The Error as Follows:

Reading "J:\Plane analysis\fluent.msh"...

Clearing partially read grid.

1028289 nodes.

5971754 tetrahedral cells, zone 29.

53145 tetrahedral cells, zone 30.

28 tetrahedral cells, zone 31.

3 tetrahedral cells, zone 32.

3 tetrahedral cells, zone 33.

31 tetrahedral cells, zone 34.

35 tetrahedral cells, zone 35.

2 tetrahedral cells, zone 36.

31 tetrahedral cells, zone 37.

2 tetrahedral cells, zone 38.

2 tetrahedral cells, zone 39.

27 tetrahedral cells, zone 40.

1 tetrahedral cells, zone 41.

5 tetrahedral cells, zone 42.

53 tetrahedral cells, zone 43.

1 tetrahedral cells, zone 44.

3 tetrahedral cells, zone 45.

10 tetrahedral cells, zone 46.

3 tetrahedral cells, zone 47.

1000000: Unable to allocate storage [323.06MB] for 12098307 faces.

Reading Faces: failed while reading section 13.

Clearing partially read grid.

Error: Read_Grid_Section: Aborted due to critical error.

Error: Read_Grid_Section: Aborted due to critical error.

Error Object: #f

Dear all,

I'm doing a two way FSI problem with Static Thermal and Fluent as my systems. Something like the video attached. While solving the system coupling threw the following error: "Update failed for the Solution component in System Coupling. The coupled update for System, Fluid Flow (Fluent), threw an exception."

In total there were four errors. See the image attached.

Anyone with any suggestions or advice is appreciated.

Regards,

Nikhilesh

**Dear Researchers**

**FSI simulation in the biological fluid problems**

**Ansys-Fluent or Abaqus or Adina?**

You know that solving the fluid and structure equations as a

**couple equation**is very valuable for FSI simulations. The power of software in the**easy meshing**of the biological model obtained from MRI is also important.However, how much is the

**solving**of fluid and solid equations**simultaneously**worth?According to the aforementioned concerns, which one of Ansys-Fluent or Abaqus or Adina software is better for biological fluid simulation such as blood circulation analysis in the vessels.

Regards

Dear researchers,

I am working on developing a reliable and accurate COMSOL model to investigate the inertial focusing of particles inside micro-channels. Although I add and define the lift forces (wall-induced and Saffman) and drag forces correctly, my results are incorrect. I believe that COMSOL's wall-induced and Saffman lift forces are not working properly. What can be done?

I would appreciate your insights on this matter.

Hello,

I went through ansys fluent dynamic meshing guide. It says remeshing can be done only on tetrahedral mesh. I still tried to implement it on hexahedralmesh. It works well. It is bit misleading for me that, when manual says it works for tetrahedral only. I din't encounter any problem. Am I correct in implementing remeshing on hex or wrong?

Many people implement smoothing and remeshing only on tet mesh. None did on hex, so I am confused.

Any lead or document or answer would be a great help.

Thanks in advance.

Regards,

Naveen

I'm trying to develop a code to solve the stream function-vorticity equations using the Finite Element Method in order to simulate a 2D incompressible flow problem. I was wondering what the pros and cons are, whether coupling a turbulence model is possible, whether formulating the boundary conditions may face difficulty and whether the evaluation of the pressure field is flawed possibly due to decoupling of the pressure variable from the governing equations. Note an accurate evaluation of the pressure field is particularly important for my case of study.

I very much appreciate helping me out.

I'm doing a simulation to determine maximum lift for a two elements wing, 30 degrees flap angle. by alternating the angle of attack.

I'm using second order accuracy K omega SST model (Re=10^6) with the transition and low Reynolds's correction turned off using ANSYS Fluent, so the model (as i read) uses wall functions as default for this case.

my Y+ is between 0 and 20, i found out that i either have to be less than 1, to use near wall modelling, or use wall functions for Y+ between 30 and 300, but my problem is that i'm between both ranges, will this affect the solution accuracy and detect separation correctly ?

Thank you

I am working on cross flow condenser.I have made CFD code based on it. My total mass should be 2.817kg every node. I am getting range of 2.817 to 3.192 kg. My highest error in percentage in some node is around 3 percent and lowest is around 0.2 percent. Can I consider my CFD coding is acceptable?

Particularly i am having confusion in deciding boundary condition for swirl part.

The origin of many, if not all, vascular diseases can be correlated with endothelial cells (ECs) mechantransduction. The mechanosensory of ECs is strongly linked to the physics of blood flow. CFD models of vascular blood flow can provide insightful information about the hemodynamic environment associated with different vascular disease. Hence, CFD can contribute to the research on ECs mechanotransduction. However, since blood flow is inherently multi-harmonic pulsatile flow and vascular geometry have complex 3D morphology, CFD models require rigorous validation practice in order to ensure that their results are as valuable as they are considered to be.

I would like to discuss the previous efforts conducted to provide consistent, reproducible and physically meaningful validation procedure for CFD models of pulsatile flow for vascular hemodynamics applications. Is there any validation resource available for public access? What would a good and reliable validation database include?

An aircraft is consist of many sub-parts , while estimating the Reynolds number and y+ value first layer height which length do we consider as the characteristic length to be used in the respective formulas ?

Hi everyone ,

I am implementing Acoustic model in FLUENT. Geometry is 2D. By using FW-H model, I am facing difficultly to understand these things. ( I have already read FLUENT manuals and one tutorial )

1) It is very important and necessary to define accurately

*in 2D geometry. I do not know this parameter. how to calculate it. my geometry is very simple, just a rectangular to 10*20 mm.***Source Correlation Length**2) What should be the

**? In 2d-cylindrical tutorial, I read it is a cylindrical wall. My geometry have 0.5 mm inlet a bottom. Is it the source zone and type will be Velocity INLET ?***source zone and type*3) Where will be the

**? I have to monitor the the time history when gas passes through from INLET ? I read one paper there was one monitoring point which is away form the inlet.. I could not understand.***receivers position*4) What is

**? I think, the under investigation portion has very fine mesh. this is called FW-H integral surface. But I am not sure about it..***FW-H integral surface*Any type of advise, guideline or tutorial will be highly appreciated. Thanks in advance..

I am trying to solve the flow over a solid sphere by using a finite volume method in the spherical coordinate system. I have discretized the Navier Stokes equation as per the Patankar Power Law Scheme. But I am not getting any results. I am attaching here my source code. If anyone has worked on the spherical coordinate system, kindly respond.

If the nodes of the mesh are updated by specifying the increment in the radius of the sphere (dR-which is calculated based on a set of PDEs), what is the best way of decomposing the mesh for parallel processing? Is it possible to use one of the existing decomposition methods in openFoam (i.e. hierarchical/manual/metis/multiLevel/scotch/simple/structured) or should the cells be manually allocated to each processor?

Can anyone an expert explain with examples or tutorials how can convert pump as a turbine using CFD code?

Hello Everyone ,

I was wondering is there any literature available on the extent of transitional regime in space and that for how long does it last ?

Regards

Aamir Sultan

Does continuity , momentum and energy laws remain conserved when we use local refinement in adaptive meshes ?

Hello Everyone !

It is alway said that SA model is apporopriate for adverse pressure gradients then how come it lacks the ability to accurately predict separation ?

Hello Everyone

I am simulating an airfoil at Low Reynolds Number flow Regime Re=10^5 , in this particular case a laminar boundary layer separates , forming a laminar separation bubble , then transition to turbulent and reatching to the airfoil . Is SA model capable of simulating such kind of flow in which three 'different behavior of flow exists ?

Regards

I wrote a CFD code in Delphi for turbulent axisymmetrical pipe flow (incompressible - SIMPLE - exponential discretization - staggered grid).

Epsilon diverge during Gauss-Seidel point to point iteration. Should i calculate k first by setting epsilon to zero? Any suggestions for the sequence.

Right now, I am calculating coefficients of linear k and epsilon discretized equations first. Then Gauss-Seidel iteration initiates for point values of k and e. Then I return to calculation of coefficients again.

I need to simulate a 2-D problem with DGFEM. I have been advised to use C/C++ for a code that delivers quick and efficient results, however, I am not very comfortable with them, and my base code happens to be in MATLAB. Would Julia be a better choice than MATLAB, comparable to the performance of C/C++?

Hello Everyone ,

Hope you are doing fine . I have this question about the reference values , that which length should one use while doing external aerodynamic CFD simulation of a full aircraft . The main objective of the simulation is to get the aerodynamic coefficients values at different angle of attacks . Should I be using full length of the aircraft as the resulting boundary layer will be formed over whole of the aircraft length ?

Your kind suggestions in this regard will be really helpful .

Aamir

I got one really good paper on

**, in which they have used***"Two phase modelling in ANSYS FLUENT"***UDF**and linked them to Governing differential equations of**VOF**Model in ANSYS FLUENT. The Paper I have attached below, in which terms to be added as source term is also given.I am going through UDF manual of ANSYS FLUENT and all the materials that I have with me for

**understanding how to link the source terms though UDF with the Governing differential equation of VOF model.**If you have any program written in C for adding the source term to governing differential equation of VOF model,

**please share your inputs on this topic**Thanks regards,

Somnath Rangrej

Mail ID: rangrej.somnath@learner.manipal.edu

I have modelled a transient flow in a microchannel in ANSYS FLUENT using 100 timesteps. I want to export the velocity at each node in excell format for all timesteps simutaneusly. Although using the export command i can only do it for each time step individually . Please advice me how to extract velocity for all timesteps simultaneusly in excell format (does not matter if there is a diferent excell file for each timestep).

Sometimes we hear somethings on stiffness problem of solution for chemical reaction modeling.

There is an option in Fluent software to figure it out.

Have you guys used it so far? tell us when and why did you use it?

Guys,
Sometimes after initializing the problem in Fluent and triggering the calculate button, a residual/residuals start from a big non-zero magnitude. For instance, to me, it in many cases happens for some convection-diffusion equation when I'm simulating combustion. Interesting point is that the results looks ok and have good agreement with experimental results. In this page:

It's said that:

"For most problems, the default convergence criterion in

**ANSYS FLUENT**is sufficient. This criterion requires that the scaled residuals defined by Equation 26.13-4 or 26.13-9 decrease to 10^{-3}for all equations except the energy and P-1 equations, for which the criterion is 10^{-6}."As it is said, the residuals need DECREASE TO 10

^{-3}. Then it means that it doesn't matter from where the residual starts, it should finally decrease to 10^{-3}.- Am I right?
- What's your opinion?

Another question:

3. Why does it happans? (I mean why does the residual start from a non-zero magnitude?) and How to figure it out?

I've attached two screenshots of the residual of a project for instance.

I recently updated my OpenFOAM version 4.0 to 6. I'm facing an issue in the direction of flow. My flow is always pointing in x direction. Hence I tried to change the flow axis in a tutorial windaroundbuildings in simplefoam. The default wind direction was 'x' axis, so there was no issues. When I changed the Uinlet to (0 10 0) I mean the flow is in y direction, still the flow is pointing in x direction. I'm concerned about this flow direction because in my real case, I need the flow to be in 'y' axis but the flow is along 'x' axis. Is this a bug in openfoam 6? (I have attached the image of the tutorials in which I changed the flow axis to be 'y' but still in paraview glyph is along 'x' axis)

Also I tried to run an interfoam solver, initially I set the writeinterval to be 0.5 then I thought of reducing it to 0.1, when the time was around 0.2 seconds to see what happens at 0.3 seconds, instead the program terminated with error 0.1 has already completed. Is it also bug where we can't adjust or reduce the writeinterval in OpenFOAM 6?