LES on isotropic turbulence

MrBHU

I am doing LES on decaying of isotropic turbulence.
I am using Rogallo's code (1981). He defined two random components of the velocity field in the plane orthogonal to k.
Q1 = sqrt( E(k)/4pi k^2 ).exp(i.theta1).cos(alpha) Q2 = sqrt( E(k)/4pi k^2 ).exp(i.theta1).sin(alpha)
Two unit vectors are defined as
e1 = ( k * omega )/ ( |k*omega| ) e2 = ( k * e1 ) / ( |k*e1| )
then
u = Q1.e1 + Q2.e2
it is supposed to get an isotropic, homogeneous velocity field.
But I can't get it, the initial velocity field I get is not isotropic. The integral length scale L11, L22 and L33 are not equal. Also u_rms = v_rms ~ 0.6, but w_rms is very small ~ 1.e-6. Can't understand why that happens ......
Anyone can give me some suggestions? thank you very much!