Application of Quantitative Background Oriented Schlieren (BOS): Investigation of a Wing Tip Vortex in a Transonic Wind Tunnel

Abstract

Background Oriented Schlieren (BOS) measurements have been performed in combination with Particle Image Velocimetry (PIV) measurements in order to derive quantitative flow velocity and density data of a wing tip vortex generated by an airfoil model of a modern large transportation aircraft in the transonic wind tunnel (TWG) of the German-Dutch wind tunnel (DNW) in Göttingen. The model has a span of 0.6m and a wing area of 0.1m2. The test was performed in the 1 x 1m transonic test section of the TWG with different flow Mach numbers (Ma = 0.5 / 0.6 / 0.7). The measurement technique BOS is still under development, nevertheless local quantitative density measurements in 2D flows are already possible. This test was performed to prove the applicability of BOS to 3D axis symmetrical flows in real wind tunnel experiments as well as the applicability of three component PIV measurements in transonic flows. The measurement system (BOS and PIV) consists of 4 digital cameras and a double pulsed Nd:YAG laser with 2x320mJ. This paper focuses on the theoretical as well as on the technical aspects of the BOS recording and evaluation methods especially for 3D axis symmetrical flows.