Two-dimensional expansion wave diffraction around a 90⁰ convex corner.

Abstract

The di raction of a one-dimensional expansion wave over a 90 corner was explored using experiment and simulation methods. Unlike studies in shock di raction, expansion wave di raction was hardly explored in the literature and therefore is considered as novel. Two independent parameters were identi ed for the present study: 1) the initial diaphragm shock tube pressure ratio, and 2) the position of the diaphragm from the apex of the 90 corner. The experimentation only considered variation in the shock tube pressure ratio whereas the simulation varied both independent parameters. A Navier-Stokes solver with Menters SST k-! turbulence model was found to adequately model the ow eld. A number of major ow features were identi ed, that occurred in the vicinity of the 90 corner. The ow features identi ed were: a shear layer which originated by ow separation near the apex of the 90 corner, a separation bubble that remained attached to a wall boundary in absence of rig-dependent e ects, and a re ected compression wave due to perturbation signals generated by di raction of the expansion wave. For a narrow-width expansion wave existing prior to di raction, it was found that after di raction a re ected compression wave developed which would steepen into an outwardly propagating, weak, cylindrical shock wave. Other major ow features identi ed were a strong indication of an oblique shock located near the separation bubble and a large wake region immediately downstream of the separation bubble. The wake region, through schlieren imaging, was found to consist of two distinct layers. The experimental results through shadowgraph and schlieren imaging have indicated large-scale turbulent structures within the separation bubble and the shear layer. Shear layer instability and vortex shedding o the separation bubble were also evident. The Navier-Stokes solver was found not to resolve the experimentally observed turbulence, the wake region and the vortex shedding.