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-   -   Turbulence in channel become laminar (http://www.cfd-online.com/Forums/main/15523-turbulence-channel-become-laminar.html)

pankaj saha August 6, 2008 05:29

Turbulence in channel become laminar
 
i am doing channel flow by LES. I have set the problem like below. Specially the mean pressure-gradient term as below. can anyone check it whethere i am correct or not? -----------------------------------------------------

My domain is: 4piH x 2H x 2piH (dimensional)

I have non-dimensionalised by H-(half height of channel)

So my actual dimension is---4pi x 2 x 2pi

Re=U_tau x H/nu =180.(nu=viscosity)

i have taken H=1.0(clear from my non-dimensional dimension). and U_tau=1.0

So, i set nu=1/180, in my code.

As, in the code i set H=1, nu=1/180. As, i am using periodic b.c, so nowhere i can put U_tau=1.0. To, ensure U_tau=1.0, i calculate the mean pressure gradient keeping , U_tau=1.0.

FROM BALNCE OF WALL SHEAR STRESS AND PRESSURE GRADIENT WE GET, DP/DX=TAU_WALL*2.0/2H.(2H=TOTAL HEIGHT OF CHANNEL)

so, from wall shear stress and mean-pressure balance, shows that, mean pressure gradien=1.0

And i am adding this constant pressure gradient=1.0, to my streamwise momentum equation.

So, during the computation of streamwise momentum equaation , at everycell, this added mean-pressure gradient(=1.0) is imposed .

also, i am using i.c with random perturbation.

Please,COULD YOU TELL, MY TECHNIQUE OF PROVIDING 'IMPOSE-PRESSURE GRADIENT' =1.0 IS WRONG OR RIGHT?

------------------------------------------------------

I am asking, because ...during the simulation, the mean value corresponding to the Re, will be settle down to the correct value.But, problem is that, my mean value doesnot become constatn but increasing enorsmously. for example, for Re=180, U_mean/U_tau=17.0 as, i have taken U_tau=1.0, so i should get U_mean=17.0 But, i was monitoring U_mean, at the outlet plane for every time step and saw that, it cross 17.0 and increasing and after a time of 67 it becomes 38.

Can you please, tell me where i am doing wrong in setting the problem or imposing pressure gradient?

Thanks----


Teresa November 9, 2010 08:16

channel flow set up
 
hi,
I noticed that you simulated the channel flow two years ago. U must get satisfied results already. Could you share the details of setup?


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