Prediction of a non-uniform freestream velocity distribution for counterrotating propeller configurations and the effect on performance/acoustic

Abstract

A methodology for predicting the performance and acoustics of counterrotating propeller configurations was enhanced by incorporating a method for computing the non-uniform freestream velocity distribution entering the propeller disc plane due to an axi-symmetric propeller spinner and airplane forebody. The non-uniform freestream velocity distribution is determined using an axi-svmmetric source panel method, and the results of the panel method are compared with the analytical results of flow about a sphere with excellent agreement. The effect of the non-uniform freestream velocity distribution is then taken into account throughout the performance prediction procedure. Existing methods are used to determine the steady and unsteady aerodynamic loads which are combined with the propeller geometry to predict the radiated acoustics. The effect of the non-uniform freestream velocity distribution on counterrotating propeller design and analysis is shown as well as comparisons with flight test results.