Application of Stereo PIV to the VFE-2 65° Delta Wing Configuration at Sub- and Transonic Speeds

The present paper describes the application of Particle Image Velocimetry (PIV) to the flow around a delta wing in a pressurized transonic wind tunnel. These investigations are the second part of International Vortex Flow Experiment 2 (VFE-2) measurements carried out at DLR Gottingen on a NASA wind tunnel model. The first part comprised surface pressure measurements by means of Pressure Sensitive Paint. These results were used to select the test cases for PIV. Flow fields for the Mach numbers of 0.4 and 0.8 and for the Reynolds numbers of 2 and 3 million at four incidences of 11, 13, 20 and 25 degree were captured within different planes perpendicular to the model axis. Delta wings with sharp as well as with rounded leading edges were investigated. Details of the stereoscopic PIV system such as the overall arrangement, the image evaluation and the flow seeding technique will be described. Techniques to overcome problems caused by density changes within the wind tunnel are described too, such as deflections of the laser light beam and camera viewing. Laser light flare on the model surface is reduced by a specially developed fluorescent paint which allows for the detection of small flow structures very close to the model surface.