Investigation of Unsteady Flow Fields in Wind Tunnels at High Flow Velocities by Means of Particle Image Velocimetry (Invited Lecture)

Abstract

Particle Image Velocimetry (PIV) is already a well established 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. This does not only give information about unsteady flow fields otherwise not obtainable but also helps to save operational time when working in a wind tunnel. Special requirements have to be fulfilled, when applying the PIV technique in large wind tunnels or at high flow velocities. Typical problems are: tracer particles (concentration, velocity lag, scattered light), use of pulse lasers (energy, repetition rate of pulses), technique for ambiguity removal (image shifting, cross correlation), 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, different possibilities to realize a PIV system for application at aerodynamic investigations will be presented and discussed in the frame of the experience gained at DLR.