DNS of Laminar-Turbulent Transition in a 3D Aerodynamics Boundary-Layer Flow

Controlled laminar-turbulent transition of a 3-D boundary-layer flow caused by localized surface nonuniformities is investigated by means of spatial direct numerical simulations (DNS) based on the complete incompressible 3-D Navier-Stokes equations and a combined 6th-order compact Finite-Difference / spanwise Fourier-spectral scheme. The considered laminar spanwise-invariant flat-plate base flow is a model of the boundary-layer flow in the front region of a swept wing, with favorable and ensuing adverse chordwise pressure gradient. The primary downstream growth and nonlinear interaction of vortex-packet modes as well as the appearance of a secondary instability mechanism leading to turbulence is investigated in detail. The effectiveness of a steady, nonlinear, upstream flow deformation of the base flow with respect to significant transition delay is shown.