Propulsive efficiency of wake ingestion

Abstract

Wake ingestion has been studied in order to develop a physics-based understanding of its effect on engine power and propulsive efficiency. A combination of analysis and testing has been employed. A control volume analysis of the one-dimensional flow through an actuator disk has been used to derive a set of equations for the power and propulsive efficiency of a propeller ingesting a wake. This analysis shows that wake ingestion reduces both the power available from the exhaust jet and the useful thrust power of the propeller. The net effect is predicted to be a reduction in the propulsive efficiency, defined as the ratio of the useful power to the power available. A simple experiment was performed to test this prediction. Wake and jet velocity profiles were measured for a series of bodies with thrusts equal to their different drags. These were used to calculate the propulsive efficiency. It is concluded that, although the propulsive efficiency is reduced by wake ingestion, the range of the aircraft is increased.