Hover Tests Of Micro Aerial Vehicle-scale Shrouded Rotors, Part Ii: Flow Field Measurements

摘要

An experimental investigation of the effects of varying the shroud profile shape on the hovering performance of micro aerial vehicle (MAV)-scale shrouded rotors was conducted, using 17 models with a nominal rotor diameter of 16 cm (6.3 inches) and various values of diffuser expansion angle, diffuser length, inlet lip radius, and blade tip clearance. The overall performance characteristics have been presented in a companion paper; this paper presents measurements made of the shroud surface pressure distributions and wake velocity profiles of some of the models. For high net shroud thrust, maintaining favorable pressure distributions over the inlet was seen to be more important than in the diffuser. Shroud thrust was increased by increasing the lip radius, decreasing the tip clearance or decreasing the diffuser angle, whereas changing the diffuser length had little effect. About 80% of the inlet thrust was borne by the inner half of the inlet lip; in addition, strong suction pressures were created by vortical flow at the blade tips. Optimizing the inlet design to take advantage of these factors could enable increases in thrust and reductions in vehicle weight. The uniformity of the wake was improved by the presence of the shrouds and by decreasing the blade tip clearance, resulting in lower induced power losses. For the open rotor, the wake appeared to contract more than that seen for larger-scale rotors.