Planar Doppler velocimetry in a large-scale facility

A planar Doppler velocimetry (PDV) system was developed and demonstrated in a small-scale facility (Mach 1.36 freejet) and then applied in a large-scale subsonic wind tunnel, where measurements were made over a delta wing at a 23-deg angle of attack. This PDV system utilized a pulsed, injection-seeded, frequency-doubled Nd:YAG laser to interrogate the flow. Back-illuminated charge-coupled device (CCD) cameras in conjunction with an iodine filter were used to record images produced by the scattered laser light, permitting the determination of the velocity at each CCD pixel, The PDV instrument also included custom software and a frequency-monitoring system composed of photodiodes, gated integrators, and a second iodine cell. With this setup, we recorded the shot-to-shot iodine-filtered and reference images and the associated laser frequency. In the freejet, mean velocities in the core were measured by PDV to within 6.4 m/s (out of similar to 260 m/s) of the value obtained by laser Doppler velocimetry. In the wind tunnel, freestream empty-tunnel measurements indicated bias and random errors of less than 2 and 4 m/s, respectively. The dominant source of random error arose from laser speckle, and the dominant source of bias error came from the characterization of the iodine filters. Measurements over the delta wing showed similar velocity ranges but smaller vortex cores when compared to the velocity field predicted by a computational fluid dynamics model.