Comparative Acoustic Wind-Tunnel Measurements and Theoretical Correlations on Subsonic Aircraft Propellers at Full-Scale and Model-Scale

摘要

Experiments have been completed on a Dowty-Rotol 4-bladed R292 propeller (ARA-D section) at full-scale in the 24ft anechoic tunnel and at quarter-scale on a geometrically-similar model in the 1.5m acoustic tunnel. Measurements were made of power, torque, and thrust, simultaneously with microphone recording of the propeller noise signal. Analysis of the third-octave and narrow-band spectra are presented for a range of rotational speeds up to a blade-tip Mach number of 0.75, for an extensive range of blade-angle settings, with tunnel airspeeds up to 50 m/s. The quarter-scale model is shown to have closely similar acoustic and aerodynamic characteristics to those of the full-scale propeller. As expected, substantially better noise measurements proved attainable in the 1.5m acoustic tunnel than in the 24ft anechoic tunnel, though perforce at smaller scale. The relevance of aerodynamic testing at airstream speeds approaching typical flight Mach numbers is also illustrated. Parametric formulae and fundamental theoretical frameworks for propeller noise prediction are discussed. While useful correlation is exhibited between the measured and predicted sound levels for the discrete tones, substantial discrepancies exist for the apparent broadband noise.