New Rotor Airfoil Design Procedure for Unsteady Flow Control

The present paper describes two different experiments performed in a transonic wind tunnel facility at DLR-Goettingen. The first experiment was conducted in order to study compressible vortices behind a cylinder and investigating the feasibility of combining two different measuring techniques: the Background Oriented Schlieren (BOS) technique and the Particle Image Velocimetry (PIV) which allow respectively to measure both density and velocity fields. The second experiment described in the present paper is done in the same wind tunnel facility where a new test section has been developed to investigate the unsteady flow about oscillating models under dynamic stall conditions. Dynamic stall is characterized by the development, movement and shedding of one or more concentrated vortices on the blade upper surface, the hysteresis loops of lift-, drag- and pitching moment are highly influenced by these vortices. To understand the very complicated unsteady flow involved, a detailed knowledge of the instantaneous flow fields is of crucial importance. With the application of the described measuring techniques it is expected to gain more insight into the problem. In recent years numerical codes based on the time-accurate solution of the Reynolds-Averaged Navier-Stokes equations (RANS) have been developed. Results from these codes are ready for comparison with experimental data. A section of the present paper is dedicated to the comparison of numerical with corresponding experimental data.