The three-dimensional time-dependent compressible Navier-Stokes equations are numerically solved to study spatially developing plane Poiseuille flows undergoing laminar/turbulent transition. NSCBC and Compact Finite Difference Scheme are used in the streamwise (x) and the vertical (y) directions, however, a classical Fourier method is employed in the periodic (z) direction. Several subsonic simulations, with isothermal walls, for different Mach numbers and perturbed with different random-disturbance amplitudes are carried out to study the effects of compressibility and the disturbances on the transition mechanism. Some of the simulations in their early transitional state show the appearance of vertical vorticity in the vicinity of the walls. High and low speed streaks are created between the counter rotating vortices and both structures evolve longitudinally, giving birth to bypass transition.

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