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Question on simulating turbulent flow around a cylinder
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Hello,
I have simulated flow around a cylinder in turbulent flow (Re=2*10^5) with the K- omega SST in 3D. However, I have a question about the vorticity field that I have attached. Why there is such let's say noise in the area where I have shown by arrow?!! I am going to share my fvsolution and fvscheme to have a better discusion. Could you give me general advice on this matter? Thank you. Code:
/*--------------------------------*- C++ -*----------------------------------*\ Code:
/*--------------------------------*- C++ -*----------------------------------*\ |
I'm still looking for your contribution.:)
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Any idea 💡??
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Is the issue that you raise a mesh sensitive issue? Do artifacts disappear when you make the mesh finer?
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Thank you dlahaye for the reply,
No it is not the issue of mesh refinement to some what. Actually, couple of hours ago I found that the problem is very sensitive with div(phi, U) scheme. What I found is that Code:
div(phi,U) Gauss LUST grad(U); Code:
div(phi,U) Gauss linear; |
I suspect the sensitivity to the discretization scheme to disappear on finer meshes.
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I will share my results with different div. Schemes.
Thanks. |
Results using various div schemes are hard to make sense of in the absence of a analytical reference solution.
My suggestion again is to try various mesh sizes. I do realize this is a nuisance as 1/ you will need to create various meshes; 2/ you will need to run on various meshes. |
I'll try it.
Thank you again dlahaye. |
Cool! Please post your results here for us to have a look at.
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Hello everyone,
I hope you have nice days. I came back after few days in response to previous posts. As you saw I came across smearing gradients for flow around a cylinder at Re=200000 with the following mesh and discretization scheme: Code:
/*--------------------------------*- C++ -*----------------------------------*\ However, in order to get rid of this issue I employed various methods in openfoam. The procedures are as below: 1) Studing the effects of the mesh refinement and transition between cells (Number of cells between layers): I adopted the same numerical scheme and used refinement level of (6,6) instead of level of (5,5) for cylinder, Nevertheless, there was not significant changes!2) Studing the effects of different numerical schemes on the same mesh: In this state, I consider previuos mesh with refinement level of (5,5) and utilized different discretization scheme whether spatial or temporal. I tested various methods for ddtSchemes (Time) , gradSchemes (Gradient) and divSchemes (Divergence) ; what I found is that just applying different methods for divergence of velocity (U) considerably affects the solution of our problem. |
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Due to attachment restrictions, I have to make multiple posts, So I apologise for that.
…2) Besides, once again on the previous mesh with a refinement level of (5,5); the Gauss linear method was kept constant as a gradient Scheme and different divergence schemes were utilized: |
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...2)
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3) Studing the effects mesh topology:
In conclusion, linearUpwind grad(U) scheme along with the O-Grig type was the best choice. If you have any complementary opinions and ideas it would be really welcome. Best Regards, Saeed Jamshidi |
Congrats for your results.
Well done! |
linear scheme is second-order unbounded. That's why you are getting those oscillations. You should never use linear scheme for divergence terms under any circumstances for RANS simulations.
Regards Update: Specified that linear scheme is not suitable for RANS simulations. |
Nice thread, but let me just address the following:
Quote:
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Thank all of you for the opinions.
I want to add another type of divergence scheme which is frequently used in openfoam tutorials for the Detached Eddy Simulation, like Code:
surfaceMountedCube Quote:
Also, I employed this scheme and it gave me satisfactory result for the IDDES method: Attachment 97957 |
Quote:
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Yep - that makes sense Saeed: linear in the LES regions and linearUpwind in the RANS regions.
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