3-D-boundary-layer transition induced by superposed steady and traveling crossflow vortices

Crossflow-induced laminar-turbulent transition and the initial stages of turbulence are investigated by means of spatial direct numerical simulations for the accelerating 3-D flat-plate boundary layer of the ”Querströmungsprinzipexperiment” of the DLR-Göttingen [1]. The complete 3-D incompressible Navier-Stokes equations are solved marching in time on the basis of a 4-order Runge-Kutta scheme. Fourier spectral expansions and 6-order compact finite differences are used for discretization in space. In accordance with the experiment, both steady and traveling crossflow modes are excited. Attention is focused on the non-linear interaction between vortical structures generated by the primary instabilities. The growth of high-frequency secondary instabilities is also observed. Classical turbulent quantities are evaluated for the region downstream of the laminar breakdown.