An in-duct to far-field phased array technique for validation of fan broadband liner performance at representative engine Mach numbers

摘要

A previously developed in-duct beamformer technique has been extended to separate out the three components of the unsteady pressure measured on the duct wall. Using data taken from a fixed axial array in the bypass duct of a scaled model fan, the extended beamformer technique is shown to be capable of separating out the broadband fan noise from other sources of noise and from turbulent boundary layer pressure fluctuations The technique is shown to provide an improved method for assessing bypass duct liner performance in terms of wall sound pressure insertion loss and identifying sources of noise other than fan noise over a wide frequency range and at engine-representative duct Mach numbers.