Particle Image Velocimetry in Mach 3.5 and 4.5 Shock-Tunnel Flows

For the e rst time, a particle image velocimetry (PIV) system was used to study high-Mach-number e ows 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 e ow is considerably more dife cult than to a continuous e ow because no online adjustments of the optics and the particle seeding can be done. Additionally, a proper seeding and timingofthefacility iscrucial.Firstwewilldiscussthemeasured velocity e eldbehind acontoured Lavalnozzle (design Mach number4.5 ). The measurement data show that thee owe eld at the nozzleexit is parallel to the nozzle axis and homogeneous as expected from supersonic nozzle theory. The average measured velocity corresponds very well to the calculated e ow velocity. The results are compared to measurements made with a conical Mach 3.5 nozzle that exhibits a diverging e owe eld. A wedge was further introduced into the parallel Mach 4.5 nozzle e ow 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 efe cient measurement method for high-speed and short-duration simulation facilities.