Application of non-isotropic resolution PIV in supersonic and hypersonic flows

The non-isotropic image interrogation technique is applied to study the compressible supersonic and hypersonic flow regimes. Supersonic flow experiments are performed in a blow-down windtunnel where the wake turbulence downstream of a wedge-plate model configuration is studied in the transonic M=1.35 regime. The hypersonic experiments are conducted in a short duration facility at Mach 6 and the flow over a sphere is studied. The technical challenges to achieve PIV measurements in compressible flows are discussed with respect to seeding techniques, particle imaging and the analysis of the recordings. Particular attention is given to the analysis of flow features such as shock waves and compressible shear layers with the possibility to enhance the spatial resolution by means of an adaptive interrogation scheme. The image interrogation method is based on the adaptation of the interrogation window shape (elliptical) and its orientation with respect to the velocity components spatial curvature. The analysis of the hypersonic flow case is performed with a fixed and free window method respectively showing that shock waves may be better resolved with the non-isotropic approach. In the case of the supersonic wake flow the measurements of the compressible turbulent separated shear layer attempts the characterization of the shear layer spatial growth rate.