A dynamic inflow-based induced power model for general and optimal rotor performance

A rigorous analytical model for lifting rotor performance in forward flight is developed that combines finite state Dynamic Inflow theory with conventional blade element theory. Dynamic Inflow is based on firstprinciples potential flow theory that relates the rotor induced inflow velocity distribution to the rotor pressure loading. The model is able to capture increased induced power at higher advance ratios not predicted by Glauert's classical momentum theory. The model provides general performance characteristics for specified blade pitch and radial twist control as well as optimum performance subject to specified constraints. The rotor is treated as an infinite-blade actuator disk including the effects of reverse flow and inflow feedback. Results confirm the singularity in rotor power found in earlier investigations and provides new understanding of the important effects of reverse flow, inflow feedback, rotor solidity, and blade root cutout. The model also directly yields power constants for a quadratic power model that may be used to quickly calculate induced power as a function of advance ratio. Results obtained using higher harmonic blade pitch control show that induced power is reduced for all conditions. With a sufficient number of control degrees of freedom, induced power approaches Glauert's minimum ideal power. Higher harmonic control also eliminates the infinite power singularity.