Instability and Sound Emission From a Flow Over a Curved Surface

Abstract

The growth and decay of a wavepacket convecting in a boundary layer over a concave-convex surface is studied numerically using direct computations of the Navier-Stokes equations. The resulting sound radiation is computed using the linearized Euler equations with the pressure from the Navier-Stokes solution as a time-dependent boundary condition. It is shown that on the concave portion the amplitude of the wavepacket increases and its bandwidth broadens while on the convex portion some of the components in the packet are stabilized. The pressure field decays exponentially away from the surface and then algebraically exhibiting a decay characteristic of acoustic waves in two dimensions. The far field acoustic pressure exhibits a peak at a frequency corresponding to the inflow instability frequency. AnalysisThis section is divided into three parts. Part 1 contains a 538/Vol. 110, OCTOBER 1988 Transactions of the ASME Copyright © 1988 by ASME Downloaded From: http://vibrationacoustics.asmedigitalcollection.asme.org/ on 06/11/2015 Terms of Use: http://asme.org/terms Journal of Vibration, Acoustics, Stress, and Reliability in Design OCTOBER 1988, Vol. 110/ 539 Downloaded From: http://vibrationacoustics.asmedigitalcollection.asme.org/ on 06/11/2015 Terms of Use: http://asme.org/terms

Radiation and control of sound from evolving wave packet on a concave-convex surface

“…The amplitude variation with time has a behavior similar to that of the mass flux variation. 17 Here, we show results of the calculated acoustic field obtained from the solution of the linearized Euler equations. Figures 6-9 show the pressure perturbation evaluated at 2-, 5-, 7-, and 11-ft radii from the center of the sources over a 180-deg arch.…”