Investigation of the density and velocity distribution of a wing tip vortex by means of stereoscopic Background Oriented Schlieren Method (BOS) and stereoscopic Particle Image Velocimetry (PIV)

In case of Background Oriented Schlieren Method (BOS) and Particle Image Velocimetry (PIV) the information about the flow can be taken simultaneously in the whole flow field. Coupling these two techniques enables the measurement of the thermodynamic state of the flow. The test in an industrial transonic wind tunnel was carried out to show the feasibility of coupling these two techniques for the investigation of axis-symmetrical flows. The wing tip vortex of a modern large transportation aircraft in the transonic wind tunnel in Göttingen was investigated by means of stereoscopic BOS and stereoscopic PIV. Thus, the density and the velocity distribution of the flow behind the wing tip were observed. Three different flow speeds (Mach = 0.5, 0.6 and 0.7) and four different angles of incidence (-3°, +1°, +2°, +3°) were investigated. Based on investigations about the possibility measuring the local density distribution with BOS accurately, with information on the position of the density variation a further development of the measurement technique was achieved by new post processing algorithms. Further on it was possible to derive criteria for setting up the BOS system in order to obtain reliable quantitative data