Direct Numerical Simulations of Subsonic Plane Poiseuille Flows Undergoing Transition

Compressible Navier-Stokes equations are numerically solved to study spatially developing plane Poiseuille flows undergoing transition to turbulence. Navier-Stokes Characteristic Boundary Conditions 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 forced with different random-disturbances are carried out to study the effects of compressibility and disturbances on the transition mechanism. Some of the simulations in their early transitional state, (i.e. DNS of Re=2500 and M=0.5 plane Poiseuille flow perturbed at the inlet with 5% of the streamwise velocity amplitude) show the appearance of ω_y vorticity component in the vicinity of the walls. This near wall vertical vorticity along with the generated streaks, located between the counter rotating vortices, evolve downstream with a longitudinal elongation.