3 years ago

Soft wall resistance as a necessary condition to validate numerical simulations in thermoacoustic heat transfer within closed cavities

Heitor H. De Barros, Leonardo S.de B. Alves

Publication date: January 2019

Source: International Journal of Thermal Sciences, Volume 135

Author(s): Heitor H. de Barros, Leonardo S.de B. Alves

Abstract

The propagation of confined acoustic waves induced by thermal excitation has been extensively examined in the literature using theoretical, numerical and experimental methods. Despite their ability to predict several important trends, theoretical and numerical studies have not been able to reproduce the long time pressure field behavior observed in experiments. We propose, in the present paper, that this discrepancy arises from the boundary condition models employed in these studies, which assumes all solid walls are hard. In other words, acoustic waves are perfectly reflected upon these solid walls. Considering acoustical resistance alone, a single parameter soft wall model that takes into account the small but non-negligible wave amplitude wall reflection losses is proposed. Numerical simulations of the Navier-Stokes equations are then performed in such a way as to reproduce four different and well known experimental studies. Comparisons between numerical and experimental results reveal that a short time agreement is possible in most cases because reflection losses did not yet have enough time to accumulate. A good asymptotic agreement, i.e. for long times, however, exists only when wall acoustical resistance is not neglected. Since acoustic reactance was neglected in this model to facilitate parameter estimation, phase errors are still present.

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