INVESTIGATION OF THE INFLUENCE OF DUCT-MOUNTED HELMHOLTZ RESONATORS ON THE SOUND FIELD OF A MODEL DUCTED PROPELLER

摘要

This study was basically an experimental investigation of the influence of wall-mounted Helmholtz resonators on the sound field of a ducted propeller, with an objective of determining the feasibility of far-field noise reduction. The investigation utilized two model propeller ducts, with an array of discrete resonator units installed at the wall surface.nPreliminary measurements, with the resonators tuned to the propeller harmonics, indicated a significant increase in the far field signature. An analytical model, illustrating the effect of wall impedance on dispersive acoustic modes, was then derived. This suggested a critical influence of the reactive impedance on the transmission loss (for a constant resistive impedance). Further experimental studies did not achieve the desired objective, but indicated the necessity for consideration of modal coupling, particularly to radial modes, if far field noise attenuation were to result.