Planar Doppler Velocimetry in a Large-Scale Facility

Abstract

AplanarDoppler velocimetry (PDV) systemwas developedand 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  ow. Back-illuminatedcharge-coupled device (CCD) cameras in conjunctionwith an iodine Ž lter were used to record imagesproducedby the scattered laser light,permittingthedeterminationof the velocity at each CCD pixel. The PDV instrument also included custom software and a frequency-monitoring system composed of photodiodes,gated integrators, anda second iodinecell.With this setup, we recorded the shot-to-shot iodine-Ž ltered 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 » 260m/s) of the value obtainedby 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 Ž lters. Measurements over the delta wing showed similar velocity ranges but smaller vortex cores when compared to the velocity Ž eld predicted by a computational  uid dynamicsmodel.