Airframe noise source localization on the basis of surface pressure

Abstract

The problem of source localization on surfaces subject to turbulent flows is addressed. An entirely new concept is presented, which does not rely on determining the source strength of surrogate sources (typically monopoles) by correlation with the actual farfield pressure as in phased array analyses. Instead, a source quantity on the actual aerodynamic surface is derived as a (small) part of the actual surface pressure fluctuations. This quantity strictly follows from the hypothesis that sound is generated at those surface points where locally the mirror principle is violated, which would hold at a plane hard wall. The statement implies that sound is generated strictly by the diffraction of an incident pressure (near) field. In that sense surface curvature is a necessary condition for the generation of sound on surfaces subject to turbulence. The source quantity is objective in the sense that it neither depends on the observer position nor on the acoustic installation environment of the surface. Furthermore, because of it’s hydrodynamic nature, it shows super-resolution compared to conventional localization. The paper closes with examples of sound generation at rounded and sharp edges.