BOS Flight Tests for 3D Helicopter Rotor Wake Characterization

Abstract

Interactions between blade tip vortices and the structural components of a helicopter play an important role in the generation of noise and structural vibrations. The detection of the exact vortex trajectories is highly desirable, therefore, especially for the case of full-scale helicopters under realistic flight conditions. The Background Oriented Schlieren (BOS) method has proven to be a reliable and scalable tool for the visualization of these vortices. To date, however, it has not been successfully applied for the reconstruction of an entire three-dimensional helicopter vortex system. In the current study, we present results from a flight test with a full-scale BO 105 in an open pit mine. A BOS measurement system consisting of 10 cameras applied to natural backgrounds was used to visualize the vortices of the helicopter under maneuver flight. Vortex filaments could be visualized up to a vortex age of 360°. From the evaluated images, a three-dimensional reconstruction of the vortex system was calculated using epipolar geometry with iterative photogrammetry. The final paper will include information about the measurement setup, the suitability of the natural backgrounds for the BOS method, the calibration process, different approaches for the reconstruction of a three-dimensional vortex system of a full-scale helicopter, as well as the aerodynamic interpretation of the results obtained.