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NUMERICAL EXPERIMENTS ON SHOCK WAVE DIFFRACTION AROUND RAMP SPLITTER USING SMALL AND LARGE SHOCK TUBES

Page 61-72

Ahmed M. Bagabir

Abstract

The experimental studies on shock wave diffraction have been done on conventional small-scale experimental shock tube which reveals spatial and temporal limitations. The wave reflected from the walls of the test section interferes with the evolution of the shear layer and its associated vortex. The computational fluid dynamics can simulate flow patterns of large-scale shock tube that are difficult, expensive, or impossible to study using measurements. The present numerical research is dedicated for diffraction of unsteady compressible flow around 172° ramp splitter using small and four-time larger shock tubes. Both scales are realistic sizes that are likely to be found in the real life applications. Therefore, the objectives of the research are to achieve a better understanding of spiral vortex evaluation, shock-vortex interaction and the associated Kelvin–Helmholtz instability that are not covered by experiment shadowgraphs. The present numerical method is a cell centered finite volume. The second-order AUSM+ scheme is applied to calculate the inviscid fluxes of the unsteady Euler equations. The simulations are performed using quadrilateral mesh. Mesh adaption of five additional levels each refined by a factor of four is applied in regions where density gradients exceed 5% of the local normalized value. Results are presented for weak and strong shock waves of the Mach numbers 1.31 and 1.59. The numerical results reveal excellent agreement with the corresponding experimental shadowgraphs. It is found that the refracted shock moving inside the vortex is affected by the rotation and centrifugal forces which have not been noted before.

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