Light-in-flight holographic particle image velocimetry for wind-tunnel applications

Abstract

Holographic particle imaging techniques for air-flow investigations are mainly limited tosmall-scale laboratory experiments. The two main reasons are the limited light poweravailable in conjunction with small tracer-particle sizes, which must be in the order of1 µm to properly probe air flows, and the increased background noise from out-of-focusparticles in deep volumes preventing investigations with higher particle densities. Toensure a good accuracy of the velocity measurements by faithful reconstructiongeometry, the evaluation of particle images is often conducted in the originalrecording set-up. The time-consuming scanning process, however, blocks the flowfacility during evaluation—a disadvantage for measurements in costly industrialwind tunnels. For an alternative, we have introduced off-site reconstruction andevaluation. In recent papers we have furthermore demonstrated principles tocope with little object light and to suppress background noise. Here we present asuccessful implementation of theses principles for wind-tunnel measurements.