FLOW MEASUREMENTS OF AN ISOLATED MODEL TILT ROTOR

Abstract : Wake measurements on the advancing side of a 0.25-scale V-22 isolated tilt rotor are presented and discussed. Three-dimensional wake geometry data were obtained using the Laser Light Sheet "LLS" technique. The position of wake segments relative to the rotor blade were acquired for a range of thrust and shaft angles. The rotation sense of the wake segments was determined. The lower thrust condition generated negative tip loading over a larger portion of the rotor disk than the higher thrust condition. At a higher thrust condition for the same shaft angle, the number of observed negative circulation vortices decreased. Two-dimensional velocity measurements were obtained using the Particle Image Velocimetry "PIV" technique. Three methods for averaging the PIV velocity data are discussed. Two of the methods account for vortex wander; both methods, however, require further refinement in order to determine which method provides more accurate results. The third method, which does not account for vortex wander, should only be used to obtain general features of the flow. For the vortices examined, approximately 100 PIV samples were determined to be sufficient for computing the average vortex core size and core circulation. The core size and core circulation of the negative vortices were smaller than the positive circulation vortices. The core tangential velocity appears to have a nearly linear relationship to the core size for the vortices examined. The fraction of total circulation in the core for both negative and positive vortices was found to be consistent with the Scully and Oseen vortex models.