Abstract:
Nonuniform flow in the transition region where a circular duct is coupled to a large chamber has been modeled to lowest order by numerical solution of the Helmholtz equation describing the acoustic field. The associated end effects are described as a complex acoustic impedance Z[inf end], which plays an important role in the Greenspan acoustic viscometer [Gillis et al., Rev. Sci. Instrum. 67, 1850--1857 (1996)]. The effects of geometry on the end effects, including the effects of chamfering sharp edges, have been calculated for a variety of orifice geometries and tested experimentally with Greenspan viscometers. A new formalism for modeling end effects by numerical solution of the coupled PDEs for the viscous and acoustic fields will also be described. The formalism can be extended to calculate entrance effects in other geometries, including thermoacoustic stacks. [Work supported by the Office of Naval Research.]