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Help! How to hold turbulence in a 2d channel flow RANS simulation

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Old   July 27, 2012, 10:58
Default Help! How to hold turbulence in a 2d channel flow RANS simulation
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dw
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Newbie here.

I am doing a 2D rans simulation to investigate some turbulence models. I am wondering how to make the flow turbulent?

For example in a simple Re_tau=180 channel flow, or a little bit more than that. Pressure gradient driven, using some low Re turbulence model, and keep the mesh having y+<1.

Then I set the initial nut=100*nu, k/e>100*delta_t, mass is kept constant on the solver's side (I am using an unsteady solver (URANS)).

But I found the flow is always laminar or laminarized. This is very annoying.

But I read so many papers, they all have a perfect velocity profile, How did they do that? Any secrets?

Or what did I do wrong?

Any ideas?

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Old   July 27, 2012, 13:44
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Originally Posted by 1/153 View Post
Newbie here.

I am doing a 2D rans simulation to investigate some turbulence models. I am wondering how to make the flow turbulent?

For example in a simple Re_tau=180 channel flow, or a little bit more than that. Pressure gradient driven, using some low Re turbulence model, and keep the mesh having y+<1.

Then I set the initial nut=100*nu, k/e>100*delta_t, mass is kept constant on the solver's side (I am using an unsteady solver (URANS)).

But I found the flow is always laminar or laminarized. This is very annoying.

But I read so many papers, they all have a perfect velocity profile, How did they do that? Any secrets?

Or what did I do wrong?

Any ideas?

--------
1/153
Could you post your velocity profile compared to the DNS at Re=180?
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Old   July 27, 2012, 13:49
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Old   July 27, 2012, 13:57
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Thanks for helping. Yes the velocity profile is here: [shared just for 24 hours]

http://f.imgtmp.com/Dcdfq.jpg
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Old   July 27, 2012, 14:59
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Is that because 2D cant sustain the turbulence structures, so to damp out all the turbulence? Or is that I should use RANS not URANS?
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Old   July 27, 2012, 15:09
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Is that because 2D cant sustain the turbulence structures, so to damp out all the turbulence? Or is that I should use RANS not URANS?

No ... you are solving a 2D statistically steady solution, you never see in RANS any other variable that zero-order statistics....
But your problem is that you are solving a smaller Re number, your profile arrives at y+ about 10 at the half-heigh!
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Old   July 27, 2012, 15:16
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I will test with other LRN models to see if my new implemented model is wrong somewhere. But have you ever use steady RANS to get a correct profile before? Which turb model did you use? Thanks

Last edited by 1/153; July 27, 2012 at 15:32.
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Old   July 27, 2012, 15:39
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RANS is perfect in turbulent channel flow, you have some wrong in your setting/input
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