Numerical experiments on stability and transition in plane channel flow

Various secondary and tertiary instabilities in plane channel flow are explored via time-dependent numerical simulations using the incompressible Navier-Stokes equations. Comparisons are made between transitional flows at Reynolds numbers 1500, 5000, and 8000. The lambda vortex, detached shear layer, and inverted vortex regions are identified and the origin of the latter is explained. The laminar breakdown of the Re=1500 flow is computed with high resolution and the nature of its ensuing hairpin eddies is clarified by numerical particle paths. The potential of center-mode rather than wall-mode transitions is proposed and the resulting flow structure is described.