Numerical analysis of pitching-rotor aerodynamics

The influence of periodic blade pitching on rotor aerodynamics is numerically investigated at a Reynolds number typical of micro-air vehicles. Blade pitching motion is parameterized using three variables, giving rise to a large parameter space that is explored through 74 test cases. Results show that a relevant tuning of pitching variables can lead to an increase in rotational efficiency and thrust, which is found to be primarily related to the occurrence of reversed von Karman street, leading edge vortex (LEV) formation and dynamic stall phenomenon. In addition, for cases where reversed von Karman street occurs, the flow is found to be quasi-two-dimensional, suggesting that quasi-two-dimensional approaches can provide relevant approximations of the global aerodynamics. Overall, the analysis demonstrates that blade pitching can be beneficial to the aerodynamic performance of micro-air vehicles and helps draw guidelines for further improvements of flapping-rotor concepts.