In the research reported here an attempt has been made to discover by experiment what physical assumptions and approximations are appropriate in the theory of cavitation microstreaming, especially for cavitation bubbles located near solid boundaries. A systematic investigation of the phenomenon has been made and its dependence on certain parameters (e.g., amplitude of sound) has been determined. The investigation has disclosed that as the sound amplitude is varied, other conditions remaining the same, the streaming changes discontinuously through several stable regimes. It appears that in order to account for the generation of vorticity one needs to assume different conditions at the boundaries for each regime. For at least one regime, a theoretical model due to Nyborg seems to be applicable; comparison made with experimentally determined streaming velocities.

Experimental and theoretical results are presented for a wall-mounted cavity in turbulent flow, oscillating at Helmholtz or depth-mode resonance, where the mouth dimensions are small compared with acoustic wavelength. A new, computerized, hot-wire method was employed to investigate the oscillating flow field in the cavity mouth. Measured wavelength of the interface wave agrees well with predictions of Michalke, using an equivalent laminar flow model based on the oscillating mean velocity profile. By means of a forward transfer function derived from the theoretical interface wave model and a backward transfer function derived from organ-pipe theory, a root locus solution of the frequency lock-in problem has been obtained. Predicted frequencies and sound pressure amplitudes are in good agreement with experimental values at the lower modes. Both resonant and off-resonant oscillation was investigated. For resonant oscillation, the streamwise slot width is required to be M−1/4 times the disturbance wavelength, where M is an integer. For situations in which the equations are applicable, the method can be used to predict design parameters for nonoscillating wall cavities in moving vessels.

Cavity tone spectra have been investigated as a function of wind speed in a low noise wind tunnel, at Mach numbers below 0.2. The cavity, a cylindrical closed pipe with a rectangular slot for a mouth opening, was flush mounted in the side of a flat plate, 30-in. downstream of the leading edge. Both laminar and (tripped) turbulent boundary layer effects were explored. Contributions to tone generation from turbulent boundary layer fluctuations, acoustic background noise, sheartone feedback coupling, and cavity resonant feedback coupling are quantitatively sorted out on the basis of theoretical models. A theory of laminar pipetones, complementing an earlier model of turbulent pipetones, is used as a basis for explaining sheartone/pipetone interaction. An empirical correction curve is introduced to take into account the slowing of wave speed in thick shear layers.

It is shown that both the Cremer-Ising and Coltman mechanisms for sound production in organ pipes are comprehended by a more general approach, based on conservation of linear momentum. By calculating force per unit area exerted by the jet on a control volume containing the mixing region, and equating this to the difference in pressure along the pipe axis, it is possible to derive an expression for acoustic particle velocity in the standing wave as a function of the jet driving flow spectrum. The momentum model of the jet-pipe interaction is able to explain the Coltman radiation symmetry effect, and also accounts for the role of entrained air in sound production. Additional spectral interaction terms, not previously noted, are found to play a significant role in the production of sound-pressure fluctuations in the pipe. The fluctuating lift force at the edge is found to contribute to the sustenance of the pipe-cavity oscillation below resonance, opposing it above resonance. In the near vicinity of the resonant frequency, edgetone effects are relatively small. Subject Classification: 6.5.