Exit-Slot Orientation on Pumping Blades for a Rotor in Ground Effect

摘要

High-resolution particle image velocimetry measurements were taken to document the evolution of the tip vortices trailed from a rotor system operating in ground effect, with centrifugal-driven (i.e., pumping) spanwise blowing blade designs. All pumping blade designs used the same intake and internal slot, with exit slots oriented at angles of 0, 30, 45, and 60 deg above the horizontal axis. Each blade set was tested in a hovering state in ground effect at a blade loading coefficient of 0.080. Additional measurements were also performed to examine the effect of mass flow rate on tip vortex diffusion. Each pumping blade designs incurred a power penalty, resulting in part from the increased profile losses associated with the exit slots. The 30, 45, and 60 deg pumping blade designs had a degraded performance when compared to that of the 0 deg pumping blade, which was hypothesized to result from negative thrust effects. At the higher thrust condition, the tip vortices trailed from the pumping blade designs persisted in the wake as concentrated regions of vorticity, and at older wake ages, produced relatively similar flowfields. However, at the lower thrust condition, the tip vortices were found to be significantly more diffused.