PERFORMANCE AND PIV-INFORMED MODELING OF A COMPOUND HELICOPTER PUSHER PROPELLER

Abstract

The objective of this study is to experimentally determine the effect a compound helicopter fuselage has on the forward flight performance of a pusher propeller through wind tunnel testing in the Glenn L. Martin Wind Tunnel (GLMWT). This systematic test campaign has built off of previous compound helicopter test campaigns at the University of Maryland (UMD) where various vehicle configurations have been tested at high advance ratios. A new pusher propeller test stand for thrust augmentation of an existing single main rotor test stand has been designed and fabricated along with a composite pusher propeller. Wind tunnel tests were carried out with three distinct vehicle configurations: isolated propeller, isolated fuselage, and finally fuselage with propeller. The effects of fuselage placement on propeller performance are investigated through measuring propeller loads along with two-dimensional three-component phase-resolved particle image velocimetry (PIV) measurements. The PIV measurements were obtained in a plane parallel to the airflow located between the pusher propeller and fuselage elements; they illustrate the aerodynamic interactions between the fuselage and propeller at various flight speeds and propeller RPMs. The PIV measurements are then used to inform two different inflow models used in Blade Element Momentum Theory (BEMT) to predict the effects of the fuselage on the pusher propeller's performance. The first model assumed the measured PIV inflow was the same across the propeller's azimuth, and the second split the propeller's disk into regions which experienced either the freestream flow or the measured PIV flow based on the projections of the single main rotor test stand's hub and support post on the propeller's disk. Flow field measurements showed a reduction in axial flow velocity closer to the propeller root, whereas at the outboard 20% of the propeller's radius, the flow remained close to freestream velocity. The azimuth-symmetric model gave more accurate overall performance predictions when the propeller was operating behind the fuselage. The thrust over power ratio of the propeller increased in this configuration compared with the isolated propeller. Overall propulsive efficiency remained similar to the isolated propeller configuration for the propeller tested.