Investigation of Instantaneous Flow Fields in Wind Tunnels by Means of Particle Image Velocimetry

Abstract

Particle Image Velocimetry (PIV) is already a well estabilished tool in many areas of fluid mechanics. For the first time the PIV technique allows the recording of a complete velocity field in a plane of the flow within microseconds. Special requirements have to be fulfilled, when applying the PIV technique in wind tunnels. Typical problems are: tracer particles, use of pulse lasers,technique for ambiguity removal,flexible and reliable installation of the recording system in the wind tunnel, automatic control of the whole measuring sequence, evaluation and post processing of PIV recordings etc. After having explained the basic principles of PIV very briefly, the experimental setup of DLR, which has been developed with the aim to be able to operate a PIV system even under the rough environmental conditions of a large wind tunnel, will be described in some detail. This PIV-system has been successfully applied to flow field measurements in the velocity range from U &#61 10 to 500 m/s. The evaluation and the post processing of the PIV recordings run fully automatical on a workstation. Finally, applications of the PIV technique at the investigation of unsteady flow fields in different wind tunnels will be presented. These examples show, that the PIV technique is a useful tool for aerodynamic investigations - in low speed flows as well as in transonic flows - in the field of grid turbulence, boundary layer instabilities, wake flow behind 2-d models, and for the investigationof transonic flows above pitching airfoils.