Review of Planar Multiple-Component Velocimetry in High-Speed Flows

High-speed flows encountered in most applications typically have very high Reynolds numbers and are often highly turbulent. Even in a laboratory-scale high subsonic or supersonic (high-speed) flow, velocities could vary over 3 orders of magnitude, and the turbulence spatial and temporal scales could span over 4-5 orders of magnitude. Exploring detailed physics of such flows presents major challenges to both experimental and computational researchers. An ultimate velocimetry technique would provide detailed, accurate, volumetric, real-time velocity data in such flows. With that being the goal, currently there are two planar velocimetry techniques that are developing rapidly into very useful tools with the potential of providing accurate velocity information in high-speed flows. The techniques are planar Doppler velocimetry (PDV) and particle imaging velocimetry (PIV). Whereas PDV has been under development for a relatively short period of time and is becoming a powerful technique, more accurate in high-speed flows, PIV is an established technique in low-speed flows and is now breaking ground in high-speed flows. The purpose of this review is to provide detailed background on these two techniques, to discuss the strengths and constraints of each technique, and to outline the areas in need of further improvement and development