Flow visualization and pressure measurements on an airfoil in high Reynolds number transonic flow

Abstract

Today most of the wind tunnels used for aerodynamic testing are not able to reproduce flight Reynolds numbers. To overcome this, a shock tube flow is used to generate a high Reynolds number transonic flow. With this technique Reynolds numbers up to 40 Mio. based on model chord length are attainable in the Mach number range between 0.6 and 0.9. Time resolved surface pressure measurements as well as flow visualizations are performed for the airfoil BAC3-11/RES/30/21. Two models of different chord lengths, 80 mm and 100 mm, respectively, have been used. The maximum Reynolds number achieved so far amounts to 21 Mio. for a free stream Mach number of 0.7. The results show that, calibrating the test section flow carefully, this wind tunnel technique is suitable to generate high Reynolds number flows allowing aerodynamic testing at low costs. It avoids the complex cryogenic wind tunnel and model technique, on the expense of relatively short running times and relatively small test section cross size. The testing time is in the order of 10 to 15 milliseconds which is sufficiently long for flow establishment and an useful measuring phase with stationary or at least quasi-stationary flow.