ON HYPERSONIC BOUNDARY-LAYER INTERACTIONS AND TRANSITION

Certain features of recent theoretical research into hypersonic flow are described, concerning boundary layers, shock layers, nozzle flows, wakes, viscous-inviscid interactions, and hypersonic instability and transition. The research is on the continuum range, for high Mach numbers and high Reynolds numbers. The fundamental area of steady, laminar, external planar flows in the hypersonic strong-interaction regime is studied first, for flat-plate and thin airfoils. The interplay of the equally thick viscous and inviscid layers, and the bounding shock, induces global upstream influence of a particularly severe kind, requiring a special computational treatment to determine the flow solution. Secondly, internal steady flow is discussed for a slender hypersonic nozzle configuration which produces a two-stage flow structure downstream of the nozzle throat. Similarities and differences between these external and internal flows are pointed out. Thirdly, properties of instability and transition of the hypersonic boundary layer, its wake and the inviscid outer layer are considered. These include the viscous and the inviscid modes within the viscous boundary layer, inviscid modes within the outer layer, their interaction, vortex-wave interactions, finite-time break-up in the unsteady interactive boundary layer, and surface cooling. Some experimental comparisons, and open problems, are also described.