Overview of PIV in Supersonic Flows

Abstract

The extension of particle image velocimetry to supersonic and hypersonic wind-tunnel flows has been achieved in the last decade. This was mainly possible with the advent of short interframing-time CCD cameras with temporal resolution allowing to obtain correlated particle images at flow velocities exceeding 1000m∕s. The most challenging aspects of PIV experiments in supersonic flows are still recognized as the seeding-particle-selection and seeding-distribution techniques. Also, the optical access for illumination and imaging require a specific attention since pressurized facilities offer limited optical access. The presence of shock waves in supersonic flows introduces regions where particle tracers slip with respect to the surrounding flow. Moreover, the particle seeding density becomes strongly nonuniform and particle-image blur can occur as a result of the strong refractive index variations. The present chapter reviews the physical and technical problems of PIV experiments and discusses the potential of such techniques on the basis of recent experiments performed in high-speed wind tunnels: double compression ramp at Mach 7 and shock-wave turbulent boundary interaction at Mach 2.