CFD Online Discussion Forums - simulation of subharmonic resonance in boundary layer transition

I meet a problem in the direct numerical simulation of subharmonic resonance in boundary layer transition.

I find the amplification of my subharmonic wave is significantly smaller than experiment data. However, the amplification and amplitude distribution of the fundamental wave are correct.

I suspect there is something wrong in my calculation of nonlinear terms in NS equations, through which the subharmonic wave obtain energy. I use spectral method in spanwise direction (with periodic boundary conditions), so the calculation of nonlinear terms are through the sine and cosine transformation. My method is based on Fasel (1990) Numerical investigation of 3D development in boundary layer transition.

Does any one meet a similar problem?

Thanks in advance.