Direct Numerical Simulation of Controlled Shear Flows

Two examples of controlled boundary-layer flows are discussed to illustrate the potential of advanced shear-flow control for drag or heat-load reduction. Delay of the drag-increasing laminar-turbulent transition, a procedure generally termed laminar flow control (LFC), is demonstrated in a three-dimensional boundary-layer as present on a swept airliner wing. Using a code for incompressible flow localized suction at the wall is applied at steady crossflow vortices exactly below the region where a strong localized high-frequency instability typically triggers turbulence, and significant transition delay is demonstrated at relatively low suction rates. Using a compressible code, effusion cooling through holes in the laminar boundary layer of a vehicle flying at Mach=6.8 in the atmosphere is simulated and investigated with respect to cooling efficiency as well as possible destabilization of the laminar flow, the latter possibly destroying the benefit of cooling. In both cases true unsteady simulations are performed to be able to correctly detect and capture flow instabilities, rendering the simulations costly. The performance of the used codes is discussed as well as the problems that will be attacked in the near future.