The initial condition for turbulence channel flow

Ma Jianfeng

I'm a freshman in DNS and want to do the direct simulation of plane turbulence channel flow. The plane turbulence channel flow has been studied widely and have many available results, So I choose this case as my start.(the flow is 3-D,the periodic boundary condtions are imposed at the streamwise and spanwise, the no-slip boundary condition is imposed at the upper and lower wall) In the simulation, I found I can't given the proper initial condition. From the literature, some authors says they start their simulation from the laminar velocity profile with random noise. So I write the following code as the intial condition of computation.

ran=1.0e-8; srand(2); //create a seed of random-number for (i=2;i<L;i++) {

for (j=1;j<=M;j++)

{

for (k=2;k<N;k++)

{

u[i][j][k]=ran*rand()/double(RAND_MAX); v[i][j][k]=ran*rand()/double(RAND_MAX); w[i][j][k]=1.0-uy[j]*uy[j]+ran*rand()/double

(RAND_MAX); ///the main flow profile

p[i][j][k]=0.0;

dp[i][j][k]=0.0;

}

} } In the computation, if I large the variable ran, then the pressure may not convergence. If I choose ran=1.0e-8 or even smaller, as the advance of time, these random noise may decrease step by step and the main flow w[i][j][k] didn't changeat all.

So who can help walk out this quandary?? Thanks a lot!!