Analysis of Single and Contra-Rotating Propellers

The high efficiency of open rotor propulsion is attractive to designers of sustainable transport aircraft configurations of the future. Modern open rotors for transonic aircraft are geometrically complex, can involve multiple stages (e.g. downstream stator or contra rotating second rotor) and typically operate under conditions where the flow over a portion of the blade is transonic. The overall net efficiency of modern open rotors can approach 86% at a cruise Mach number of 0.8 leading to significant fuel savings in comparison to turbofan engines. Modern open rotors are considerably quieter than the propfans of the 1980s.

Modeling of open rotor configurations to predict the thrust produced and power required is believed by many to be outside the capabilities of traditional blade element analysis but this may be because of blade geometrical and aerodynamic modeling deficiencies not an inherent deficiency in the blade element approach. Presented in this memorandum is a description of the modeling approach behind a newly developed Blade Element Momentum Theory analysis code called PyRotor that is written in the Python programming language. The underlining theory and functionality of the code are described. Several rotors, ranging in complexity from a simple two-blade propeller up to a modern CR rotor system, are analyzed and compare favorably with previously published measured data.