Application of PIV technique to transonic flows in a blow-down wind tunnel

Particle Image Velocimetry (PIV) is increasingly used to investigate unsteady velocity fields instantaneously. At DLR an experimental setup for PIV has been developed which can be operated in transonic flows under the rough environmental conditions (noise, vibrations) of a large high speed wind tunnel. This PIV-system has been successfullyapplied to flow field measurements in the velocity range from U = 10 to 500 m/s. The evaluation and post processing of the PIV recordings runs fully automatical on a workstation. Two different aerodynamic investigations of instantaneous transonic flow fields around a bluff cylinder and around a NACA 0012 airfoil have been performed in a blow-down wind tunnel. The experience gained during these experiments and some technical improvements of the PIV technique which are necessary to enable its application in transonic flows are described