Particle image velocimetry in Mach 3.5 and 4.5 shock-tunnel flows

For the first time, a particle image velocimetry (PIV) system was used to stud high-Mach-number flows in a shock-tunnel facility with velocities of more than 1.5 km/s and measuring times in the millisecond range. An application of PIV to such a transient high-speed flow is considerably I more difficult than to a continuous flow because no online adjustments of the optics and the particle seeding can be done. Additionally, a proper seeding and timing of the facility. is crucial. First we will discuss the measured velocity held behind a contoured Laval nozzle (design Mach number 4.5). The measurement data show that the flowfield at the nozzle exit is parallel to the nozzle axis and homogeneous as expected from supersonic nozzle theory. The average measured velocity corresponds very well to the calculated flow, velocity. The results are compared to measurements made with a conical Mach 3.5 nozzle that exhibits a diverging flowfield. A wedge was further introduced into the parallel Mach 4.5 nozzle flow to study the seed particle performance downstream of an oblique shock. The measured results are also in good agreement with calculated velocities from oblique shock theory. PIV has, therefore, proven to be an efficient measurement method for high-speed and short-duration simulation facilities.