Recording and Evaluation Methods of PIV Investigations on a Helicopter Rotor Model.

Particle image velocimetry (PIV) experiments have been performed in order to derive quantitative flow velocity data of rotor blade tip vortices of a large-scale helicopter model and during a three weeks wind tunnel test. Today, three-component PIV wind tunnel tests at moderate speeds and observation distances can be performed on routine basis. The wind tunnel experiments, on which we will report, have been performed on a rotor model of 4m diameter in the 6m x 8m open test section of the Large Low-speed Facility (LLF) of the German-Dutch Wind Tunnel (DNW) operated at 33m/s. The rotor model used was a 40% Mach scaled model of the MBB Bo105 of the German aerospace establishment DLR in Braunschweig. The rotor consists of four hingeless blades with 0.121m chord length, rectangular blade planform, and -8° linear twist. The airfoil was a NACA 23012 with tabbed trailing edge. During the test, the model was mainly operated in descent flight conditions where blade vortex interaction dominates the noise emission. The rotor rotational frequency was 17.35Hz leading to a tip speed of 218m/s. The PIV system consisted of five digital cameras and three double pulse Nd:YAG lasers with 2x320mJ each, which were mounted onto a common traversing system in order to keep the distance between the cameras and the light sheet constant while scanning the rotor wake. The length of the traversing system was in the order of 10m, the height approximately 15m. More than half a Tera Byte (650GB) of PIV raw data had been recorded at various positions on the advancing and the retreating side. The measurements have been performed in the frame of the HART II program (Y. Yu 2002) and include noise, blade pressure, blade deformation and flow data by means of PIV. This paper focuses on the technical aspects of recording and evaluation of the 3-C PIV