Further Investigation of Micro Hovering Rotor Aerodynamics using Time Accurate Computations

In this work, a compressible Reynolds Averaged Navier Stokes (RANS) code is used to further investigate the aerodynamics and flow physics of conventional hovering micro-rotor which operates at low Reynolds and Mach numbers. The current work also serves as a step towards developing a computational methodology that can serve as a predictive tool for a variety of conventional and unconventional rotary wing MAVs. Compared to previous work by the authors, where the calculations were done in the blade fixed frame, the present computations are done in a time accurate manner in the inertial frame, facilitated by the implementation of time-accurate preconditioning. The effect of leading edge geometry is investigated by looking at blunt and sharp profiles and comparing with experimental data. The thrust and power is reasonably well predicted for the sharp leading edge geometry. The performance prediction for the blunt leading edge geometry is slightly inferior because of discrepancy in the modeled geometry. Blunt leading edge geometry shows poorer performance compared to sharp leading edge geometry mainly because of large pressure drag acting at the blunt front. Blunt leading edge geometry also shows significant leading edge laminar separation bubble which results in complete separation near the tip. Flow visualization shows that the tip vortex flow-field is very complicated with the presence of secondary vortices and additional vortices formed due to separation near the trailing edge. The tip vortex profiles are reasonably well predicted, but the inadequacy of the turbulence model leads to some discrepancies during tip vortex formation. The swirl velocities for the micro-rotor is found to be significantly larger compared to full-scale rotor, which can be one of the reasons for additional power loss in the smaller scale rotors.