Structural resonance influences on flow-induced acoustic amplification

Abstract

An experimental investigation of the influence of structural resonance on the acoustic response to vortex shedding is presented. Flow-induced amplification of acoustic energy is of interest in the field of combustion instability in solid rocket motors. Baffles located at the junction of motor segments can cause generation of flow vortices and amplification of acoustic energy. This investigation examines the hypothesis that an additional amplifier of acoustic energy is provided by the vibratory response of these baffles. Flow through a cylindrical cavity is interrupted by annular baffles that extend radially inward from the cylinder walls. Baffle configurations are controlled to induce various frequencies of vortex shedding. Acoustic pressure and baffle vibratory responses for various combinations of baffle resonance and vortex shedding frequency are recorded using a modal analysis technique. This provides the database used to quantify the influence of vortex shedding frequencies and structural resonance on acoustic pressure amplitudes. A theoretical model of the interactions of different baffle configurations with chamber acoustics is presented and shown to be in general agreement with the acoustic pressure amplitudes measured in the test section. [Work supported by Morton Thiokol, Inc.]