Hello, all: While now I am going to do some Isotropic turbulence simulation, but no idea on how to impose the initial condition, seems like I have to generate the fourier modes and do the 3D FFT or DFT, but I am wondering how to generate the fourier modes. Thank you in advance, please indicate me some hints or reference, thank you!

Hi,

Look for a paper by Rogallo (1981) or (1977). It is technical report from NASA or Stanford. I do not know the exact reference but it is cited in many papers on DNS. To generate an initial field I give each mode a random amplitude (between -1 and 1) and a random phase (between 0 an 2 pi). Then project the velocity field to obtain a divergence free field. Compute the spectrum and specify the desired spectrum. Then correct the amplitudes so that the desired spectrum is obtained. Check if it is isotropic etc. Rogallo does it in a more advanced way but the end results are very similar.

Good luck.

Thank you sir.