Science topic

# Turbulence Modeling - Science topic

Explore the latest questions and answers in Turbulence Modeling, and find Turbulence Modeling experts.

Questions related to Turbulence Modeling

In fluid mechanics and computational fluid dynamics (CFD), the fluctuating velocity components u' v' w'′ represent the turbulent fluctuations in the velocity field. These components are used to model the turbulent behavior of fluid flow. The prime notation (u' v' w') denotes the deviation of the velocity from its mean value (

*U*,*V*,*W*).For laminar flow, turbulence is generally not considered, and the flow is assumed to be smooth and ordered. In this case, the fluctuating velocity components (u' v' w') are essentially zero.

In CFD simulations using software like FLUENT, you typically specify the turbulence model and relevant parameters to simulate turbulent flows. Common turbulence models include the k-epsilon model, the k-omega model, and the Reynolds stress model. These models provide equations for the turbulent kinetic energy (

*k*) and the turbulent dissipation rate (*ϵ*), from which the fluctuating velocity components (u' v' w') can be derived.In FLUENT, you will need to set up your simulation by defining the geometry, boundary conditions, and fluid properties. Additionally, you'll need to specify the turbulence model and provide initial conditions for the turbulence variables. The software will then solve the governing equations, including the RANS equations and turbulence model equations, to obtain the mean flow field and turbulence quantities, including the fluctuating velocity components.

The specific steps may vary depending on the version of FLUENT and the turbulence model chosen, so it's recommended to refer to the FLUENT documentation or user guide for detailed instructions based on your simulation setup.

Some turbulence models such as DES and LES are incompatible with the overset mesh in fluent software. Is it possible to avoid or handle this problem vie UDF file and how?

Dear CFD Researchers,

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

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

Thank you for your comments.

Kind regards,

Guven

Hello all,

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

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

Regards,

Armin

Hello everyone

I hope you are doing great, I am working on offshore VAWT, and trying to simulate a vawt in ansys fluent. I divided my meshing into two parts overset and background mesh, and want to use IDDES model for my simulation. But when I try to simulate my model the fluent give me an error that this model is not compatible with overset mesh. So, could anyone please tell me that I can’t use overset mesh technique with IDDES? or I can use this technique by changing any solver setting?

Thank you so much for your time!!

Many researcher are using python all over the world. Few young researcher are interested to learn more to develop computation skills in application to planetary science, space science research and Helio-physics. If any experts who want to teach such interested researcher, I will make a common platforms in which we can learn together virtually.

How use y plus value with different types of turbulence models in cfd ?

Hello! We pump the contour of a metal tube with a diameter of 3 mm with oil with a viscosity of 0.0031 kg / m * s (abt. the viscosity is 4 times higher than that of water). We are interested in the pressure for pumping this circuit (at the inlet).

When validating the model in Ansys CFX with k-epsilon default settings, the difference between the result and the experiment reaches 100%, although the mesh is adjusted according to the tested and validated model, only on the water (with a maximum deviation of 10%). The Reynolds number in a pipe with a diameter of 3 mm is Re=2500, that is, we are dealing with a transitional flow regime, and the pipe is not hydraulically smooth in terms of the critical number Re=20d/"roughness".

Tell me, please, maybe for this mode it is necessary to use another turbulent model, for example, "Reynolds stress" or "k-epsilon" set up somehow differently? Maybe there are works in which a similar problem is solved, or there are works with recommendations on the use of turbulence models?

Hello all
I am simulating flow over a sphere at Re = 881 where Drag coefficient must be almost Cd=0.5. I simulate it using both using laminar and Turbulent models(KOmegaSST). for laminar simulation, I get Cd ~0.5 but fort the Turbulent simulation, first of all it takes very long tome to converge and even after convergence, it gives Cd~0.65(Actually it has not fully converged yet, see attached figure). Now I have two questions;
1- what happens if I use turbulent model to simulate laminar flow?
2- when should I expect convergence based on the attached figure?

I need some urgent help . I have been simulating the steam cracking furnace from certain papers namely

1.) CFD simulations of steam cracking furnaces using detailed combustion mechanisms

2.) Impact of radiation models in CFD simulations of steam cracking furnaces.

In both these papers furnace geometry, reaction, composition of the fuel and the models applied are similar. But in both these papers , the maximum flame temperature was achieved at the height of 1.5m . But when I try to simulate these papers using the same flow , combustion , turbulence model in the ANSYS fluent , same as that of the papers my maximum flame temperature reaches at 2.1 m and has a longer flame when compared to those above paper. Can someone please help me why this is happening even though I have applied the same case as that of papers

I am attaching the papers for the reference

Hello,

I am running a 3D density based transient problem with Spalart-Allmaras turbulence model. After few iterations I am getting Negative Nut in xxx cells. I tried to search the cause, but not successful in finding answers. Could anybody help me in understanding from where this problem arises?

In openFOAM, there are multiple options for choose in LES, such as WALE model, Smagorinsky model and so on. Which one is suitable for dynamic mesh and why ?

I am a bigginner of LES simulation, as far as I know , the only difference between them is WALE model includes the rotation rate in the calculation of

*νsgs, and*Smagorinsky not. What else should I take into account in simulation?In compressible flows, would improvements based on the SST K-Epsilon turbulence model , such as the use of AI，be a more promising direction in engineering. ten or thirty years from now, will the most commonly used model be the Reynolds stress model or its deformation, or will DES be the most commonly used simulation method.

Hello,

I am trying to simulate phase change during turbulent flow in comsol multiphysics, for that I require to add an additional sink term at the end of turbulent kinetic energy and energy dissipation rate equation which is 'k' and 'epsilon' equation in turbulent model to include the effect of solidification in the turbulent flow. Can somebody please suggest how to do that.

any suggestion will be greatly appreciated.

-Akshay

I tried writing a udf for the turbulence model needed to validate a study. The wall boundary conditions (epsilon and f) specified for the v2-f model are available in the code I wrote. While I get consistent results for velocity and cp values in my validation, I do not get the correct result for v2 and f values. Is there a problem in the code or am I not transferring the boundary conditions to fluent correctly? I would be glad if you help me in this regard.

Hi

A 3D numerical simulation project involves a turbulent flow of water in a tube with a constant heat flux entering the surface.

This numerical simulation needs to be validated by a similar article that has simulated the K-Omega SST Turbulence model.

Please guide me if there is an article I can refer to.

Thanks

Hello everyone

I have attached the integral length scale definition where upper limit goes up to infinity, but in some references practically they integrate from 1 to where autocorrelation function becomes zero (and naturally negative part is not included), references like;

1- Davidson, L., 2018. Fluid mechanics, turbulent flow and turbulence modeling.

*Chalmers University of Technology, Goteborg, Sweden (Nov 2011)*.2- Tritton, D.J., 2012.

*Physical fluid dynamics*. Springer Science & Business Media.which one is correct,

1 - Integrating up to where R11 goes to zero

OR

2 - Should I include negative part too?

Thanks,

Farzad

Hello, I want to publish a research paper on the assessment of CFD turbulence models, I need an airfoil geometry to start with. where can I find airfoil geometry or profile? and its experimental data, cd and cl values or cl alpha values? I have searched for experimental data, but unfortunately, I did not find any.

Can you please advise me about where to find airfoil geometry and its experimental data?

what type of airfoil should I choose for the assessment of different turbulence models?

Hello everyone,

In my research project i have air flow velocity and temperature distribution simulation from supply and return air duct in non furnishing control zone, which turbulence model is better ?

Hello all,

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

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

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

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

Here are my questions:

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

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

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

I appreciate your comments.

Hi all,

I am going to use either Ansys CFX or Ansys Fluent solver to simulate flow past a semi-submerged rectangular cylinder, as shown in Fig. 1. The main goal here is to achieve an accurate prediction of pressure distribution over the cylinder, which seems to be particularly reliant on the capability of the CFD model to predict the separation and the reattachment of the flow correctly. I would appreciate any tips regarding the following questions.

**Q1**. How important is the choice of the turbulence model? Which models are superior? Could the flow be modelled as being laminar at all?

**Q2**. How important is the approach to the free surface? Could the free surface be modelled as a free-slip wall to reduce computational costs? Is it necessary to precisely track the free surface using the VOF model for this study?

**Q3**. What are the most appropriate boundary conditions for the simulation?

**Q4**. Which is more suitable for this problem? CFX or Fluent?

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

internal flow over cylindrical, rectangular and ellipse shapes.

outside is rectangular shape.

Hi all, I have been encountering this problem shown in the pic with simulations with parameters:

- RNG k-epsilon Transient
- Pressure-based Coupled scheme
- massflow inlet and pressure outlet BC with Intensity 5% and Hydraulic Diameter 0.012m for Turbulence Specification Method
- URF and COurant number 0.2 while Turbulent Viscosity 1
**Three boxes for Frozen Flux Formulation, Warped-face Gradient Correction, Higher order term relaxation** - Timestep size 0.002 and 25 iteration/timestep

The problem occurs when the three boxes are checked, the number of cells overlimit starts very low and gradually builds up to such level after around 20 timesteps. When the three boxes are unchecked, overlimit cells range between 1 and 9 and disappear soon after.

Online posts suggested me to drop timestep size, max iteration per timestep, and URF but they don't seem to work for me. Especially when URF is quite low already. Assuming I wish to keep those 3 boxes checked, does anyone has any ideas?

I have been bugged for long. The model is also attached. Thanks a lot!

Can we plot u-plus (U/Utao) Vs y-plus (Y/Ytao) plot for a turbulence model in ANSYS-Fluent post processing? Basically, I want to be ensure that the model will take into account the gradients in the viscous sublayer.

I'm using Ansys Fluent to model a rotating cage setup to monitor Flow Accelerated Corrosion.

Is kw sst suitable for analyzing the flow over an airfoil after the airfoil has been stalled? specifically if we want to model the effective body of a stalled airfoil, can I do it with Kw sst or is there any better turbulent model to choose.(computational power is also limited )

Hi all,

I am modeling a high-velocity (200 m/s) flow of water vertically entering the air. The water is supposed to hit the wall after traveling a 0.5 mm distance. The flow is highly turbulent, and I am using the k-omega phase-field approach for modeling.

The problem is that once the jet approaches the wall, the problem stops converging (Error: maximum number of segregated iterations reached). Any idea what is the root of the problem and how to solve it?

Thank you for your time in advance,

Majid

First I simulated scramjet problem using k-e model in fluent. The results are validated using literature after that necessary modification was done in boundary conditions using same mesh. The results shows expected trends. After getting this results I refined the mesh and changed the turbulence model to K-w. The results are showing similar trends as k-e models but equivalence ratio of critical phenomenas are higher than k-e model. I want to know what are the possible reasons of high differnce of equivalence ratios? How I can verify which models are giving correct results?

Hi everyone,

I am trying to simulate turbulent flow over a sphere with the following conditions:

Freestream velocty= 100m/s

ambient density and viscosity

Sphere diameter = 0.82 m

Reynold's number = 5.6 x 10^6

experimental Cd = 0.195

Sphere enclosure = 42 x 28 x 28 m3

mesh Size 4.5 milllion

I tried using S-A model and K-omega SST model in fluent, using which I am getting Cd=0.14. which is almost 26% error.

Any suggestion as to how may I improve the result?

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

In my study, I have two cases for CFD which I performed on Ansys Fluent,

1)

**oscillating flow over a solid cylinder**(blunt face perpendicular to flow direction)and

2)

**solid cylinder**(blunt face perpendicular to flow direction)**oscillating in the stationary fluid**. It involves dynamic meshing.In both of the above cases, I am using the

**SST k-w turbulence model**for this simulation.[ ie what should be the input value for

*Turbulent Kinetic Energy*and*Specific dissipation rate*? ]What does it means if both these values are equal to 1.0?

I have attached a graph representing drag force as a function of time [calculated from the case (2)]. I want to know what might be the possible reason for this behavior in the initial time.

My

**UFD**(equation for velocity of moving cylinder): V = 1.0 * cos(2*3.1415*1.55*t) m/s.**The initial spike? why does this occur?**

**The decreasing amplitude?**

**What would be the expected output if this was calculated for longer time values (amplitude behavior after 5 secs)?**

Fluid: incompressible (water)

calculation settings:

time-steps = 500, time-step size = 0.01 sec, maximum iterations = 500.

Meshing (element size = 1.0 mm, element shape = triangles)

In case of turbulent flow over an irregular shape, how can we find the first layer thickness near the walls of the irregular boundary.?

For flow over a flat plate, the skin friction co-efficient can be found by the direct formula, for irregular shapes how can we find the skin friction coefficient.

Some commonly used turbulence models include k-epsilon, k-omega and shear stress transport (SST) models. The k-epsilon model is a best candidate for flow away from the wall (e.g. free surface flow region), while the k-omega model is best suited for near the wall flow region (e.g. adverse pressure gradient flow region). The choice of most appropriate turbulence model for any turbulent flow problem may be extremely difficult for young computational fluid dynamists, hence the need for this germane question.

I'm reading this paper.

This paper is claiming there is a problem in k-epsilon model.
Because in k-epsilon model, we assume that eddy viscosity(

*ν*) is isotropy. But actually in real world, eddy viscosity(_{T}*ν*) is anisotropy for high Reynolds number and is isotropy for low Reynolds number. It means there can be error when we consider flow with high Reynolds number._{T}And I have a question in uploaded figure.
How he can calculate fluctuation velocity?

What I know is
fluctuation velocity can be calculated only when we assume that eddy viscosity(

*ν*) is isotropy(like k-ε model)._{T}When we use k-ε model, we can find k(Turbulence Kinetic Energy) by T.K.E transport eqation and k is same with '½(u'

^{2}+v'^{2}+w'^{2})'.Then if k(T.K.E) is found, we can calculate u', v' and w'

because u', v' and w' are same each other by assumption of isotropy.

But in this paper, author claims that we should consider flow as anisotropy and he suggests new Eddy viscosity(

*ν*) with new Cμ. (I've uploaded expression of Cμ by picture.) So I think it is impossible to calculate fluctuation velocity because flow is considered as anisotropy._{T}But there is a fluctuation velocity profile that is calculated by CFD.
And I think author calculated fluctation velocity using root mean square and T.K.E

Because we can find desription in figure that means he calculated fluctuation velocity by root mean square.
(Figure 8: Profiles of rms velocities perpendicular (v) and parallel (u) to the wall in the impinging jet)

So it looks like contradiction to me.

How fluctuation velocity is calculated in anisotropic flow?

Actually I've thought that assumption of isotropy can be possible in the impinging jet sometimes.
Because impingement occurs nearby wall, so there is a low Reynolds number nearby wall by No slip condition(dominant molecule viscosity).
But, eventhough my deduction is right, I can't understand why there is a difference between v' and u'.
In the case that r/D=2.5, there is a difference between v' and u' that I've marked in uploaded picture.
Difference between v' and u' means this flow is anisotropy and this is contradiction against author's claim also.

Also I've infered about the one more reason why calculation of fluctuation can be possible in this paper.

I don't know well but what I've heard is

In RSM(Reynolds Stress Model) is suggested by the same claim of this paper.

I've heard RSM is suggested because flow with high Reynolds number is anisotropic in real world

and this is different with original k-ε model.

So in RSM, it is possible to calculate the each fluctuation velocities(u', v' and w') in anisotropic flow.

So RSM and this author's model has same purpose that pursue to consider anisotropic flow.

And RSM can calculate the the each fluctuation velocities(u', v' and w').

So I think this author's model can also calculate fluctuation velocity in the same reason.

Eventhough I don't know how RSM calculate each fluctuation velocities(u', v' and w'), I've tried to infer.

Summary

Anisotropic flow by using new eddy viscosity that has direction - Calculated fluctuation velocity

: I think there is a contradiction.

Left side: Anisotropic

Right Side: Should be isotropic

→ ???

Calculated fluctuation velocity - Difference between u' and v'

: I think there is a contradiction.

Left side: Isotropic

Right Side: Anisotropic(Different fluctuation velcity.)

→ ???

I'm not good at Turbulent.

I'm just Senior.

I don't have bachelor's degree yet.

But I'm interested in Turbulence.

But I'm confused now :(

Please help me.

Thanks :)

can one use turbulent models for studying quasi-steady flows in pipeline

Hello everyone.

I'm working on a flow simulation in an axial pump. in the literature, they recommend that y + should be kept below 1. however, my results have shown that y + is greater than 10.

how can I keep y + below 1?

Note 1: I am using TurboGrid for the mesh and I am using SST as the turbulence model.

Note 2: I am using TurboGrid as a mesh generation tool.

I am designing a turbine and predicting the

**Performance of the Vertical Axis Turbine**. I have the experimental results of the same turbine with me. The problem is**after the optimum TSR, the performance of don't go down**its continuously increasing and goes above the Bitz limit. May be its**not concluding stall due to high TSR**. How do i resolve it?Its a

**steady state Analysis****Geometry -- Mesh -- CFx**

Doubt i have but need help to resolve,

* I unable to capture the correct

**boundary layer**, if it so then how could i capture it?*Maybe i am using Turbulence model which is not correct, But i have chosen shear stress transport which is be better choice, mabe?

* Also share if you any any other.

I will be

**very thankful**, and please make it**urgent.**Hi.

I'm trying to simulate a fluid through a vertical channel, width = 0.2 cm - height = 60 cm - fluid == water - inlet v = 1, using the 2D model in COMSOL. Due to the characteristics mentioned a turbulent model is needed. When choosing Algebraic YPlus method the no-slip condition in the vertical walls states (u,v) = (0,0), which is what I thought, but when using the k-epsilon or k-omega model for de NO-SLIP condition (u,v).(nx,ny) = 0 [u = 0 and v is free] which i don´t understand why. Can anyone explain why in k-e or k-omega don'y use velocity=0 on the walls?

Thanks in advance

Dear CFD Fellows,

Is there a decision table, diagram or software you use for turbulence model selection? What I'm looking for is not a table with information for each model, but rather a visual with decision steps such as "if the flow contains a-b-c, these models can be used". In the relevant case, after following the characteristic factors of your flow, I expect turbulence models to be proposed in the last section that can best define the flow.

Thank you for your interest.

Best regards,

Güven

Dear CFD Fellows,

Is there a decision table, diagram or software you use for turbulence model selection? What I'm looking for is not a table with information for each model, but rather a visual with decision steps such as "if the flow contains a-b-c, these models can be used". In the relevant case, after following the characteristic factors of your flow, I expect turbulence models to be proposed in the last section that can best define the flow.

Thank you for your interest.

Best regards,

Güven

Hi all,

I'm planning to simulate flow past a floating body using CFD method with the main purpose of investigating its stability against hydrodynamic forces. A sketch of the problem is presented the the figure attached.

It seems that an accurate estimation of pressure field, and therefore hydrodynamic forces, is heavily dependent on correct prediction of flow topology, particularly separation and reattachment of the flow.

I'm wondering what turbulent models would best handle this problem. I would appreciate it if you provide details and specific reasoning.

Regards,

Armin

I have watched videos about wall function on youtube but still confused about understanding viscous sublayer, logarithmic region, and wall functions. I couldn't find relevant material. Where do I find these topics? Can someone suggest some material regarding viscous sub-layer/logarithmic region and to understand y+ (wall functions)?

Turbulence model for blood flow simulation

Hi everyone

I am working on a shell and helically coiled tube heat exchanger with laminar flow through the shell and turbulent flow through the coil tube. I have performed iterations for coil by selecting different types of turbulence models but in each case, energy starts to diverge after some iterations (images attached).

What is the possible reason for this?

**Can you suggest where can I find video lectures on turbulent flows or turbulence modelling? Are there any video lectures on understanding turbulence modeling? Or any books to understand turbulence modelling? Can someone please help!**

**i have a project on how different turbulent models can be used on Naca aerofoil. and i am not knowing how to find material to understand turbulent flows.**

in turbulent flow calculation is it acceptable to use an y+ of 15 with a wall function in k-e turbulence model?

I am performing CFD simulation upon NACA 4418 airfoil at 45 m/s free steam velocity and Reynolds number of 3 million. I am following a particular paper where the experimental results of NACA airfoils are shown. The turbulence model I am using is k-omega SST turbulence model and the transition is ticked on. The mesh is also properly refined and since my computational power is limited, therefore I am choosing my y+ value to be greater than 30. But the following problems are observant from my simulation

01. Lift coefficient seems to be around the mark but the error percentage is still a bit above 10%

02. Drag coefficient is the real issue as it is exceeds the supposed value and produces.much higher value. Almost double the value that I want

What is the issue here and what should I do? I have been going through the theory behind drag and lift coefficient and the Computational process used behind but it's not helping me so far and I really need help regarding this right now.

Thank you very much

hi everyone
I need a little help here;
Im new to fluent and recently I am trying to simulate a two phase flow in a pipe-tank system where I want to see and analyse the intake vortex with the air core.
i am using vof+cls and les as turbulance model,
I don't have problem with convergence but after simulating 100s of the flow, I can't see the formation of vortex and air core of in getting sucked in to the pipe.
can any body help? has anyone experienced this problem too?
I really need help at this point📷

Hello guys,

I am running a simulation of a mixing tank in unsteady-state( transient) with turbulence model SST K-omega and multiphase model VOF. And I gave a number of time steps as 10000 and time step size as 0.0003 and max iteration as 50 and the solution is converging at each time step. So my question is how do I know my simulation is completed ? or I need to wait till 10000-time steps to complete?

Thanks in advance

Regards

Johnny

I am performing CFD simulation over a NACA 4418 airfoil on Ansys FLUENT and I have collected a data chart of NACA (from 1945) for the purpose of validation.

The Reynolds Number chosen for this CFD simulation is 3,000,000 and the free stream velocity is 45 m/s. Since the simulation for my case is 2D simulation both the characteristics length and area is 1m. The value of y+ considered is 1 and that is ensured by calculating the wall spacing and putting that on First Wall thickness and I have even gone through Report in Ansys FLUENT to check the maximum facet value is below 1. I have used both Spalart Allmaras and K-omega SST Turbulence model. But the following problems are prevalent:

01. For Spalart Allmaras Turbulence model,my lift coefficient is within the range i.e less than 5% difference in between but drag coefficient is way too much high in value sometimes even 200% more

02. For K-omega SST Turbulence model, my lift coefficient is significantly higher in value and as Angle of attack increases this difference gets higher but the highest it gets is below 30% however drag coefficient is also over predicted but in this case the difference is around 50% higher.

I have tried it again for both Turbulence model with a bit more refined mesh but the value of lift coefficient increases in both the cases and but the difference for drag coefficient decreases for K-omega SST Turbulence model

I have been trying this for months now and haven't come to a proper solution. I tried everything at my disposal. Read aerodynamic books and gone through understanding how it is represented on CFD but so far I am not able to find the solution. If anyone can explain it to me what is going on for my case and how can I find a solution for this, that will be really helpful and appreciated.

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,

I am interested in broadening my understanding of the physical assumptions needed to simplify its mathematical description. From these assumptions i will to choose a suitable turbulence model to run the simulation in Ansys.

The problem is fairly basic;

Inlet flow conditions: Velocity in= 44.2 m/s, Mach number inlet = 0.128, atmospheric total pressure and temperature. Turbulent boundary layer thickness @ 4H upstream of the step is 1.9 cm.

Outlet flow conditions: Fully developed flow.

Any advice would be much appreciated

Kind regards

Anton

I want to determine the aerodynamic coefficients of a 2D model (solid boosters). To be clear with the model, It is a 2D axisymmetric model, with blunt nose and flared aft body. There is a plume exiting from the nozzle. The jet plume interacts with the freestream flow, to form plume induced flow separation (PIFS). The interaction will affect the aerodynamic coefficients.

Experimentally the axial force coefficient was found to be decreasing at increased jet pressure ratio (Jet pressure/free stream pressure). I've solved it using pressure based solver with standard, K-e turbulence model (I've tried using other turbulence model too). But results from Ansys Fluent showed no change with change in jet pressure ratio.

Am I missing something or is there any other method to find axial force coefficient.

I am trying to run a transient simulation of a stirred tank reactor. Initially, I am simply trying to using water as the only fluid with the k-epsilon turbulence model. I ran the steady-state simulation first and then in the same workbench's fluent file, I simply changed the option of steady-state to transient and set the simulation to run using for 0.0008-sec timestep, 2000 timesteps, 25 iterations per time step (in order to use that steady-state data as the initial condition for the transient case). I had also used report definition function for plotting turbulence kinetic energy as a function of time and had used the option of autosave for every 5 steps along with export data of certain parameters for every 5 steps. (pl find the ss)
But after around 200 timesteps, I am getting the error of (Error: GUI-domain-label: no domain selected Error Object: 1522351816) and the simulation stops at the next iteration. I am able to click ok and the simulation runs for another timestep but the error crops up again every timestep.

Both PANS (Girimaji, 2006) and TFLES (Pruett et al, 2003) provide a self-consistent formulation that allows one to recover RANS versus DNS at opposite limits. Are the two approaches fundamentally different (e.g., in the sense that RANS vs LES employ different ansatz and thus yield different types of closures to be modeled: the Reynolds stress vs the subfilter stress)? Or are they conceptually the same approach, independently developed and thus mainly differing in preferred modeling choices/perspectives?

(note: I am unfamiliar with PANS and only marginally familiar with TFLES; apologies for any misinterpretations)

I want to add the penalty term as you suggested in the paper "Topology optimization method with finite elements based on the k-ε turbulence model" Could someone guide me on how to add the penalty terms for Eq. (11) and (12) as shown:

Hi everyone,

I'm simulating a 3D turbulent pipe flow using the SST K-W turbulence model in ANSYS Fluent. Is there any quantity among the postprocessing quantities that represent "eddy size" or "eddy length scale"? If there is not such a quantity, How can I define it in Fluent?

Thank you.

The methodology I am using was

Type- 2D Axis-symmetric behaviour

Flow domain is divided into finite number of unstructured quadrilateral cells

2D double precision, implicit, density based solver of flux type Roe-FDS

2 equation SST k-w turbulence model and RANS energy equations are solved

Air of ideal gas density as fluid with 3 coefficient Sutherland’s viscosity

Pressure far-field, stationary wall and ensured no slip condition

Free stream conditions

Mach number 6

Pressure 1064 Pa

Temperature 234 K

Thermal condition for wall : constant wall temperature of 300k

Turbulence intensity of 5% and Viscosity ratio of 10

Green gauss node based gradient

First order upwind discretization scheme for first few iterations and followed by second order upwind for further till convergence

Higher Order Term Relaxation, Convergence Acceleration for Structured Meshes and Warped face gradient correction were enabled

All the residuals were set to 1e-06

Hello

Just before I start I am new to CFD modelling and I am trying to simulate a numerical wave tank with a wave of amplitude 0.1m and wavelenght of 1.561m using stokes third order. I am using the VOF method Implicit model with 2 Eulrian phases. The turbulence model is K-omega SST and I am using a water as my second phase where I have selected compressible so it is able to interact with the air. I have set up numerical beach at the end of my domain and the BC I am using are as follows.

Inlet-Velocity inlet

outlet-pressure outlet

Atmosphere-pressure outlet

bottom and side walls-Wall(no slip)

cylinder-wall(no slip)

I am using the PISO algorithm and have decreased the relaxation factors for momentum,k and omega. For some reason I am not able to reach similar results to an experiment. I am not to sure where I am going wrong. If anyone could help I would be extremely grateful.

Thanks in advance.

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.

Hi everyone

I'm doing a steady state simulation using ANSYS fluent and k-epsilon turbulence model to investigate thermal mixing in a T-junction and I need to get a temperature contour at a specific time steps. How can I achieve that?

Any help will be much appreciated. Thanks in advance.

I'm currently working on a project that is using the SST k-w turbulence model. This model, reads velocity flow on the near wall region of a bluff body as well as the far wall region which is the combination of k-w and k-e turbulence model. The SST k-w model can be the best approach in solving this type of flow problem. The only issue is defining this model onto the CFX pre process.

Hi all. I am running simulations on a compressor fluid domain (Turbocharger compressor for a passenger car) in Ansys fluent 19.3. I am using tetra element and k-omega SST turbulence model. But y+ is still high after refinement. How to reduce to get y plus value <5 ? Could someone give me any suggestion.

Hi

I am trying to model an impeller rotating at a certain angular speed using MRF technique in Ansys fluent. Overall i expect clean attached flows and I am not really interetsted in resolving the boundary layer as I am more interested in studying the mixing of 2 liquids by the impellers. As i understand K-omega reliazable model is computationallly expensive and more for resolving the boundary layers. Which turbulence model is better for my flow as I want to keep my model light weight so that it is easier for convergence and computationally less expensive. Your advise will be really appreciated

Thanks/Regards

I am running a simulation for a turbocharger compressor fluid domain with turbulence model k-omega SST.

I am going to refine the mesh as the solution does not converge. What I know is that for a turbulence model k-omega, the Y plus value has to be <5.

I am looking to calculate the Y plus value before running the simulation.

Currently, I have a model of 3 Million of mesh elements.

Can someone explain what total mesh element number approximately should I refine to reach the Y plus value of <5?

I have problem in making my turbine simulation work with SST turbulence model

the other models: k-e, k-omega, BSL converge without problems