Cavity-enhanced jetting sound produced by a baffled piston
When a circular piston vibrates within an aperture of a baffle, the flow within the annular gap between the piston and the baffle is opposite in phase, which causes a reduction in the radiated sound. That is, the acoustic power is always less than in the absence of a leaking edge flow. However, when the piston is backed by a cavity, the overall acoustic power can be increased. This thesis focuses on approximating the effect of the ‘leakage’ for a piston of radius a in a cylindrical cavity of radius b within a rigid baffle. First we consider the piston within a baffle without a cavity, which leads to a reduced acoustic power, then we examine the two cases of a closed cavity and an open cavity. The acoustic power is found to increase when the piston vibrates close to a resonant frequency of the closed or open cavity. The smallest resonant frequency fmin depends on the cavity depth and end-correction. The maximum ‘gain’ in acoustic power ~ 10 dB which depends on the nonlinear edge flow and also depends on the ratio a/b, the aspect ratio b/L and ζ0/b, where L is the cavity depth and ζ0 is the amplitude of piston displacement.
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