On the origin of streamwise vortices in braid regions for compressible mixing layers

The origin of initial streamwise vortices in braid regions and their relationship with deformed spanwise are numerically studied via direct numerical simulation (DNS) the compressible mixing layer a convective Mach number (Mc) 0.4. Through an analysis fast Fourier transform on DNS data, two low-rank velocity models (vd vs) developed to demonstrate that both all originated from linear superposition fundamental norm mode [mode (1, 0)], pair oblique modes [modes ±1)], mean mode. Further investigations reveal that, downstream vortices, increase amplitude ratio (Ao/An) between ±1) 0) leads formation vortex regions. As Ao/An further increases, reaching threshold rotation motion exceeds irrotational deformation 0), generated aforementioned path for provides mechanism support our flow visualization results emergence precedes field.