ON SIMULATION AND ANALYSIS OF INSTABILITY AND TRANSITION IN HIGH-SPEED BOUNDARY-LAYER FLOWS

The simulation of instabilities and laminar-trubulent transition in hi gh-speed boundary-layer flows represents one of the major computationa l challenges of the decade. By taking advantage of recent advances in computational science and instability theory for compressible flows, w e have formulated an approach to this problem that combines parabolize d stability equation (PSE) methodology with spatial direct numerical s imulation (DNS). The relatively inexpensive PSE method is used to expl ore the parameter space, to compute the early (weakly and moderately n onlinear) stages of laminar breakdown, and to provide inflow condition s for the spatial DNS, which is then used to compute the highly nonlin ear laminar-breakdown stage. The approach is made feasible by an accur ate and efficient DNS algorithm, which has been implemented in paralle l on a GRAY C90 supercomputer. The design of the DNS algorithm is disc ussed in detail, with emphasis on factors that affect both accuracy an d efficiency. The method is applied to the investigation of the lamina r breakdown of the boundary layer on an axisymmetric sharp cone in Mac h 8 flow. Techniques for analysis of the resulting data are also addre ssed, including novel computational flow imaging procedures.