Numerical Analysis of Flow-Induced Noise by Vortex-Edge Interaction

J. Ocean Eng. Technol. 2004;18(5):15-21.

KANG HO-KEUN,KIM EUN-RA

Vortex-Edge의 상호작용에 기인한 유동소음의 전산해석

강호근,김은라

경상대학교 기계항공공학부ㆍ해양산업연구소,전북대학교 토목공학과

Keywords: Edge Tone Edge, Lattice Boltzmann Method, Feed Back, Sound Speed

핵심용어: 음, 래티스볼츠만법, 피드백, 음속

Abstract

An edge tone is the discrete tone or narrow-band sound produced by an oscillating free shear layer, impinging on a rigid surface. In this paper, we present a 2-D edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle, using the finite difference lattice Boltzmann method (FDLBM). We use a modified version of the lattice BGK compressible fluid model, adding an additional term and allowing for longer time increments, compared to a conventional FDLBM, and also use a boundary fitted coordinates system. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of ${alpha}$ = 23. At a stand-off distance, the edge is inserted along the centerline of the jet, and a sinuous instability wave, with real frequency, is assumed to be created in the vicinity of the nozzle and propagates towards the downstream. We have succeeded in capturing very small pressure fluctuations, resulting from periodical oscillations of a jet around the edge. The pressure fluctuations propagate with the speed of sound. Its interaction with the wedge produces an non-rotational feedback field, which, near the nozzle exit, is a periodic transverse flow, producing the singularities at the nozzle lips.