COMPUTATION OF QUADRUPOLE NOISE USING ACOUSTIC ANALOGY

Acoustic analogy computations of vortex shedding noise were carried ou t in the context of a two-dimensional, low-Mach-number laminar how pas t a NACA 0012 airfoil at chord Reynolds number of 10(4). The incompres sible Navier-Stokes equations were solved numerically to give an appro ximate description of the near-field flow dynamics and the acoustic so urce functions. The radiated far-field noise was computed based on Cur ie's extension to the Lighthill analogy, This study emphasizes an accu rate evaluation of the Reynolds stress quadrupoles in the presence of an extensive wake. An effective method for separating the physical noi se source from spurious boundary contributions caused by eddies crossi ng a permeable computational boundary is presented. The effect of reta rded-time variations across the source region is also examined. Comput ational solutions confirm that the quadrupole noise is weak compared w ith the noise due to lift and drag dipoles when the freestream Mach nu mber is small. The techniques developed in this study are equally appl icable to hows in which the volume quadrupoles act as a prominent nois e source.