▶︎ CANCELED: GALCIT Colloquium
Laminar-turbulent transition for high-speed boundary layers is very complex and is therefore still a major unresolved topic in Fluid Dynamics. Compared to low-speed boundary layers, major additional difficulties arise because several instability mechanisms become relevant for Mach numbers higher than about 4. In the nonlinear transition regime, these instability mechanisms can compete and/or interact with each other, thus rendering the nonlinear transition stages highly non-unique. The understanding of high-speed boundary-layer transition is required for developing reliable transition prediction methods that are applicable for the design and safe operation of high-speed flight vehicles. Transition to turbulence in supersonic/hypersonic boundary layers is associated with considerable increases in heat transfer. Appropriate measures to guard against the heating caused by transition and turbulence are expensive and/or result in significant weight penalties. In our research we have successfully employed Direct Numerical Simulations (DNS), using our in-house developed Navier-Stokes codes, for extracting the relevant nonlinear transition mechanisms for several wind-tunnel experiments. In this presentation, the use of DNS as a tool for nonlinear transition investigations will be introduced and discussed in detail. Then results from simulations for several wind tunnel experimental conditions will be presented for a range of Mach numbers.