Laser Velocimetry and Blade Pressure Measurements of a Blade-Vortex Interaction

An investigation of the flowfield characteristics around a rotor blade during a blade-vortex interaction (BVI) was conducted at the NASA Langley Research Center by the Army’s Aeroperformance Division and the Boeing Defense and Space Group, Helicopter Division, during a wind tunnel test in the 14-by 22-Foot Subsonic Tunnel. A two-component laser velocimeter was used to measure the flowfield near the rotor blade and blade-mounted surface pressure transducers were used to measure the local blade pressure during a BVI event. This paper presents a summary of the velocity measurements which indicate the presence of a vortex in the flowfield, vorticity calculations as the blade intersects the vortex, and blade surface pressures during a BVI. The following conclusions can be made from this investigation: 1). The streamlines of velocity show the blade intersecting a vortex, and the blade surface pressures indicate that the vortex passes mainly beneath the rotor blade. 2). Vorticity calculations from the experimental velocity data point to the existence of both positive and negative vorticity in the flowfield. 3). Initial comparison of the data with the calculations of two lifting-line analysis codes indicates that these lifting-line methods are not sophisticated enough to model the complex BVI interaction.