Abstract: Several prototype flows typical of the spanwise large-scale rolluop interactions are investigated through using the direct numerical simulation method. These phenomena have been captured experimentally in the transition region of the free shear layer for a long time. A highaccuracy upwind/symmetric compact difference hybrid method is developed and is used to solve the two-dimenmsional compressible Navier-Stokes equations. A fifth-order upwind compact scheme is employed to discretize the convective flux terms with the help of the Sieger-Warming flux- splitting technique, while a sixth-order symmetric compact scheme obtained by Collatz is selected to discretize the transport flux terms. The three-stage third-order explicit Runge-Kutta algorithm found by Wray is introduced for time-marching. The temporally-developing compressible shear layer is disturbed by the most-unstable viscous wave and its subharmonic modes obtained numerically by linear stability analysis. The fine-scale struCtures...