Computational Investigation of Microscale Shrouded Rotor Aerodynamics in Hover

Abstract

A compressible Reynolds-averaged Navier–Stokes (RANS) solver is used to investigate the aerodynamics of a microscale shrouded rotor configuration in hover; to evaluate the predictive capability of the computational approach and to understand the flow physics of the microscale shrouded systems. The overall performance is well predicted for a range of rotational speeds. The shrouded configuration shows improved performance over the free rotor, mainly seen as an increase in thrust. The thrust produced by the rotor in the shrouded configuration is lower than that of the free rotor, but the thrust generated by the shroud more than compensates for the deficit. The thrust produced by the shroud is identified to come from two main sources. First, the low pressure created primarily by the blades and partly by the tip vortex around the shroud inlet generates large shroud thrust at sections near the blade location. Second, the suction created by the flow accelerating around the shroud inlet generates additional thrust and becomes the primary source of thrust production at shroud sections away from the blades. The low pressure at the core of the tip vortex can help in enhancing the flow acceleration. A study of the effect of various shroud parameters shows that the diffuser angle and diffuser length have a secondary influence on the performance of the system, whereas smaller tip clearance and use of elliptic shroud inlet significantly improve the overall performance.