Numerical investigations of laminar-turbulent transition for a hollow cylinder flare wind tunnel model at Mach 5

Numerical investigations were carried in order to investigate the transitional shock boundarylayer interaction on a hollow cylinder flare geometry at Mach 5. The influence of the flare angle and the leading edge radius on the topology of the separation bubble was also investigated. The geometry and flow conditions are matched, as closely as possible, to those of the experiments in the Mach 5 Ludwieg Tube (LT5) at the University of Arizona (UA). Base flow calculations using various CFD codes carried out indicate that for the flow conditions and flare angles considered, a separation bubble develops downstream of the leading edge of the hollow cylinder. For relatively small flare angles a steady separation bubble is obtained. As the flare angle increases, the bubble topology becomes increasingly complex and “bubbles within the bubble” are observed. Additionally, it is shown that the bluntness of the leading edge, while keeping the flare angle constant, has an impact on the separation and reattachment locations, and subsequently on the size of the separated region. Calculations for low amplitude three-dimensional wave packets revealed that both axisymmetric and oblique waves are amplified while propagating downstream. Preliminary simulations employing a broadband forcing method, designed to emulate a “natural” transition scenario similar to wind tunnel experiments, confirm the presence of instabilities in the shear layer.