Localisation of Flap Edge Sound Sources by Use of Spectral Analysis and Flow Investigation

Abstract

Results of an experimental study dealing with flap side edge noise of a blunt flap are presented. The purpose of this research was the localisation of dominant noise sources in that region. This has been done by use of surface pressure measurements and parallel acoustic measurements in the near field of the flap. Additional flow field examinations have been undertaken to relate occurring flow features to the radiated noise and thus get a better understanding of the physical source mechanism. The unsteady surface pressures on a wing flap model were recorded by miniature pressure transducers mounted at the flap side edge. The positions of the pressure transducers were defined by use of oil flow patterns, revealing the dominant flow structures such as the flap side edge vortex and its position for an angle of attack of 9 and dierent flap angles ( 9 -36 ). The pressure transducers were mainly located along the path of the flap side edge vortex, as this vortex was assumed to be the main reason for the flap side edge noise. An inflow microphone has been used for the acoustic measurements, which were taken at dierent positions on a circle around the model to get directivity information. Comparison of microphone and pressure signals using spectral methods allowed localisation of the noise source. The flow field in the region of the flap side edge has been resolved by use of 3 component particle image velocimetry (3c-PIV) in a water tunnel and 2c-PIV in a wind tunnel in planes perpendicular to the main flow direction. Furthermore, the root mean square (rms) values of the measured velocities were calculated from PIV results.