In-flight validation of aero-vibro-acoustical excitation models

Abstract

Coherence lengths of the turbulent boundary layer pressure fluctuations were measured in flight on the A320 "ATRA" test carrier. A 3-window array was used in order to characterize the pressure fluctuations. The problem of an unknown flow direction was approached by utilizing the two-dimensional sensor distribution and a 2D fitting method rather than a 1D fitting method. Using the analysis, both, lateral coherence length, longitudinal coherence length, and local flow angle were measured. The coherence lengths were compared to model predictions and the importance of taking the flow angle into account was confirmed. The turbulent boundary layer pressure fluctuations in the aft section and in the front section were transformed in the wavenumber domain. Effects of the point spread function were removed using DAMAS2.1. The resulting source maps were wavenumber filtered and the separated spectra of hydrodynamic and acoustic surface pressure fluctuations were determined for the front- and the aft section.