harmful refrigerants such as CFCs. Another advantage of these devices is the very small number of moving parts A low Mach-number compressible flow model for the simulation of acoustically driven flow in a thermoacoustic stack is constructed. required, potentially making them highly reliable.
The model is based on the assumption that the acoustic wavelength Unfortunately, thermoacoustic refrigerators often suffer is much larger than the characteristic hydrodynamic lengthscale. from poor efficiency. Means to overcome this limitation is Thus, a simplified description of the flow is obtained which still the subject of several ongoing efforts which, in particular, retains the essential features of acoustically induced velocity oscillations near solid boundaries. A vorticity-based formulation of the target more sophisticated stack and/or enclosure designs governing equation is derived which relies on the Helmholtz decom-(e.g., [11][12]). However, these efforts are faced with sevposition of the velocity vector into irrotational and divergence-free eral difficulties, due to lack of fundamental knowledge components. Irrotational motion is used to represent the action of regarding the flow structure in the neighborhood of the acoustic waves. Meanwhile the divergence-free velocity component is used to capture the nonlinear vortical perturbations due to no-stack and the essential features of flow-acoustics interacslip boundaries. A simplified version of the model is applied to tions. analyze unsteady flow in the neighborhood of an idealized thermo-
The analysis of thermoacoustic devices has in large part acoustic stack which consists of a periodic array of thin plates placed relied on quasi-1D approximations. In particular, interacin an acoustic standing wave. Computed results are used to analyze, tions between the acoustic wave and the stack are typically for different stack configurations, the nonlinear response of the flow to different acoustic driving amplitudes and frequencies. In studied using the Stokes solution for an oscillating stream particular, it is shown that the flow is dominated by the motion of over a plate, or analytical solution of oscillating 1D flow vortices which result from the shedding of boundary layers from within a slot [6, 13]. The resulting predictions have been the edges of the stack. The dependence of energy losses on stack extensively tested against experimental data (e.g., [5,8]).
configuration and operating conditions is also examined. แฎ 1996 Briefly, very good agreement between quasi-1D theory Academic Press, Inc. and experiment is obtained when the ''drive ratio,'' defined as the ratio of acoustic pressure amplitude to mean pressure, is small. When the drive ratio is large, however, sig-