10 kHz laser-induced schliere anemometry for velocity, Mach number, and static temperature measurements in supersonic flows

Abstract

A new, to the best of our knowledge, technique for measuring velocity and Mach number in freestream flow is discussed and demonstrated. The technique, laser-induced schliere anemometry, uses a laser to write a laser-induced schliere in the flow, which can then be imaged using high-speed schlieren imaging. Here, we use a laser-induced plasma from the focusing of nanosecond-duration laser pulses from a pulse burst laser to write the disturbance. The resulting localized index of refraction gradient left from the plasma is tracked well beyond the plasma emission lifetime using schlieren imaging, and velocity is found from tracking or through a simple correlation analysis. The blast wave is also used to independently determine the Mach number via the Mach cone effect, which provides information about the mean static temperature. This technique shows great potential for use in characterizing freestream flow in supersonic facilities and is demonstrated here in a Mach 2 blowdown facility and a Mach 4 Ludwieg tube.

Multi-depth focused laser differential interferometer based on chromatic aberration

“…Finally, with the system shown to be able to function in the same way as a typical FLDI system, a practical velocity measurement capability was demonstrated. The spherically weakening laser-induced blast wave propagates at the local speed of sound (∼343 m/s) [24,25]; therefore, if functioning correctly the system should produce the same result. The raw data in Fig.…”