Pulse-burst PIV in a high-speed wind tunnel

Abstract

Time-resolved particle image velocimetry (TR-PIV) has been achieved in a high-speed wind tunnel, providing velocity field movies of compressible turbulence events. The requirements of high-speed flows demand greater energy at faster pulse rates than possible with the TR-PIV systems developed for low-speed flows. This has been realized using a pulse-burst laser to obtain movies at up to 50 kHz, with higher speeds possible at the cost of spatial resolution. The constraints imposed by use of a pulse-burst laser are limited burst duration of 10.2 ms and a low duty cycle for data acquisition. Pulse-burst PIV has been demonstrated in a supersonic jet exhausting into a transonic crossflow and in transonic flow over a rectangular cavity. The velocity field sequences reveal the passage of turbulent structures and can be used to find velocity power spectra at every point in the field, providing spatial distributions of acoustic modes. The present work represents the first use of TR-PIV in a high-speed ground-test facility.

Time-Resolved Measurements of Turbulent Mixing in Shock-Driven Variable-Density Flows

“…At conventional high-speed resolutions, Wernet 22 and Beresh, et al . 23 have made PIV measurements over hot and cold jets, supersonic jet in cross-flow and transonic flow over a cavity at acquistion rates ~ O (10 kHz ). Similarly, Wagner, et al .…”

Extending the Frequency Limits of "Postage-Stamp PIV" to MHz Rates

“…The full extent of the jet-in-crossflow experiment is given using conventional 10-Hz PIV [10], with the vertical component of the mean velocity field shown positioned in its far-field location. Superposed are the fields of view for both the 25-kHz pulseburst PIV described in [1] and the postage-stamp PIV [2]. The small size of the postage-stamp PIV window is evident, little more than a point measurement.…”

“…The most common means of measuring velocity spectra such as hot-wire anemometry and laser Doppler velocimetry generally fail to achieve the necessary frequency response, which can require 100 kHz or more. In contrast, time-resolved particle image velocimetry (TR-PIV) using a pulse-burst laser [1] recently has demonstrated an ability to directly measure spectral content at 400 kHz by confining the laser energy to a small field of view and windowing the camera to a small array [2]. Image sequences exceeding 4,000 frames were acquired, but by necessity for a small array of only 128 × 120 pixels, giving rise to the moniker of "postage-stamp PIV.…”

Measurement of the Flow Field Generated by Multicopter Propellers

“…It was proved that using this solution significantly improved the light scattering compared to micron-sized droplets. The authors of Reference [22] used a pulse-burst laser as part of a time-resolved PIV method. This made it possible to visualize the flow under high-speed and turbulence conditions.…”