Performance and Acoustic Prediction of Counterrotating Propeller Configurations

A numerical method using the analytical techniques of Lock and Theodorsen as described by Davidson is used to predict the performance of a counterrotating propeller. The counterrotating propeller configuration was analyzed over a range of different front and back disk rotation speeds with constant speed propellers, yielding such overall performance parameters as integrated thrust, torque, and power, in addition to radial variation of the blade thrust and torque. The geometry, overall performance, and radial load distribution is then used with a modified form of the Ffowcs-Williams Hawkings equation as applied by Succi for compact acoustic sources to calculate the resulting sound field at various observer locations. Since the unsteady component of the noise from a counterrotating propeller configuration is minimal in the plane of the propeller disk, this approach is limited to predicting noise levels for observer locations in this region. Currently, several methods are being studied to approximate the unsteady loading on the propeller, which would allow computation of both the steady and unsteady noise levels as generated by this class of propeller configurations.