Shock-wave-detection technique for high-speed rarefied-gas flows

This paper introduces a shock-wave-detection technique based on the schlieren imaging for continuum and rarefied-gas flows. The scheme is applicable for any existing two-dimensional flowfields obtained by experimental or numerical approaches. A Gaussian distribution for a schlieren function within the shock-wave region is considered. This enables the authors to access any desired locations through the shock (e.g., shock center, or leading- and trailing-edge locations). The bow shock-wave profile is described via a rational function, which could be employed for the estimation of shock angle. The relation between pre- and postshock flow properties along the shock wave with a high resolution can be investigated by using this technique. The technique is verified in a novel way based on the well-known gas dynamics curves (i.e., flow-deflection angle vs shock angle and shock polar diagrams). High-speed continuum, near continuum, and rarefied-gas flows over a wedge and cylinder are considered for evaluation of the proposed technique. The results show a very good agreement with existing analytical relations for continuum flow.