Index of content:
Volume 113, Issue 6, June 2003
- AEROACOUSTICS, ATMOSPHERIC SOUND 
113(2003); http://dx.doi.org/10.1121/1.1562647View Description Hide Description
The linearized equations of viscousfluid flow are used to analyze the diffraction of a time-harmonic acoustic plane wave by a circular aperture in a rigid plane screen. Arbitrary aperture size and arbitrary angle of incidence are considered. Sets of dual integral equations are derived for the diffracted velocity and pressure fields, and are solved by analytic reduction to sets of linear algebraic equations. In the case of normal incidence, numerical results are presented for the fluid velocity in the aperture and the power absorption due to viscous dissipation. The theoretical results for power absorption are compared to previously obtained results from high amplitude acoustic experiments in air. The conditions under which the dissipation predicted by linear theory becomes significant are quantified in terms of the fluid viscosity and sound speed, the acoustic frequency, and the aperture radius.
113(2003); http://dx.doi.org/10.1121/1.1573636View Description Hide Description
The present work deals with an experimental investigation of flow of air through a square-edged circular orifice at the downstream end of a circular duct. Self-excited acoustic oscillations at the natural duct modes are observed for certain flowvelocities when the orifice is sufficiently thick. For a specific Reynolds number based on the orifice diameter and the mean jet velocity the jet forks into two trains, with the alternating vortices falling into the same branch of the forked train. Whereas this phenomenon has been reported earlier to have occurred when the density ratio of the jet is less than 0.72, the present results show that it is possible for a jet having the same density as the ambient atmosphere. The jet forking is coincident with jump in the acoustic frequency from one natural acoustic mode to another with comparable amplitudes of both the modes.