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

Holographic particle imaging techniques for air-flow investigations are mainly limited to small-scale laboratory experiments. The two main reasons are the limited light power available in conjunction with small tracer-particle sizes, which must be in the order of 1 *mm to properly probe air flows, and the increased background noise from out-of-focus particles in deep volumes preventing investigations with higher particle densities. To ensure a good accuracy of the velocity measurements by faithful reconstruction geometry, the evaluation of particle images is often conducted in the original recording set-up. The time-consuming scanning process, however, blocks the flow facility during evaluation - a disadvantage for measurements in costly industrial wind tunnels. For an alternative, we have introduced off-site reconstruction and evaluation. In recent papers we have furthermore demonstrated principles to cope with little object light and to suppress background noise. Here we present a successful implementation of theses principles for wind-tunnel measurements.