Investigation of supersonic boundary layers by DNS

The capabilities of modern DNS methods will be demonstrated by two examples of activities currently pursued at the Institute for Fluid Mechanics at the Technical University of Dresden. As the first example, transition in the boundary layer along a compression ramp at Mach number M=5 is investigated. The compression-ramp flow shows many generic features of those in more complex geometries. The deflection shock generated by the compression ramp causes the boundary-layer to separate. A clear separation of acoustic and vorticity effects is observed. Compact finite differences of higher order with a localized ENO-scheme allow to capture these physical phenomena [1, 2]. As the second example, Investigations on laminar-turbulent transition for high-speed flows at hypersonic Mach-numbers will be presented. Dissociation takes place above a temperature of T>2000K within the boundary layer, a temperature which is reached easily at Mach-numbers above M=5. Additional degrees of freedom for the energy must be taken into account by employing a vibrational energy equation. Chemical reactions take place which are modeled by a 5-species model proposed by Park [3]. Further details on the chemical modeling can be found in Ref. [4, 5]. Controlled disturbances can be introduced by means of a disturbance strip at the wall which is also capable to model point source disturbances. Results will be shown for free-flight conditions at an altitude of H=50Km and at a speed of M=20. Experiments for qualitative validation of the results are available in Ref. [6].