Measurement of Vortical Structures on a Helicopter Rotor Model in a Wind Tunnel by LDV and PIV

With increasing use of civil helicopters the problem of noise emission of helicopters become more and more important within the last decade. Therefore, helicopter noise has been subject of many research projects (1). Blade Vortex Interactions (BVI) are known as a major source of impulsive noise. As BVI-noise is governed by the induced velocities of tip vorticies, it depends on vortex strength and miss-distance, which itself depends on vortex location and orientatioand convection speed relative to the path of the advancing blade. Therefore, the study of these phenomena is of particular interest for progress towards quieter helicopters. Such vortical structures at a helicopter rotor model in a wind tunnel has been studied by optical measurement techniques, since only non-intrusive techniques are capable to obtain velocity data within the rotor plane. Measurements of local flow vectors at positions close to the rotor blade tips were performed by three component Laser Doppler Velocimetry (3D-LDV) and conventional (two component) Particle Image Velocimetry (PIV)