Wave propagation through regions of non-uniform temperature distribution

Sound wave propagation through regions of non-uniform temperature distribution in a gas was studied numerically. The main objective of this study was to determine the impact of temperature gradients on the sound wave parameters and to evaluate the effectiveness of using glow discharge plasma in an ambient environment as a sound barrier. Sound attenuation through the hot gas region was studied systematically for a range of sound wave and thermal field parameters. In this work, the one-dimensional and two-dimensional cases were considered where the compressible unsteady Euler's equations together with the ideal gas state equation are solved numerically using finite difference scheme and finite volume scheme, respectively.; The one-dimensional case was a baseline analysis where, the propagation of planar sound waves at zero incidence angle (sound propagating normal to the region) was investigated systematically for various shapes and lengths of the high-temperature region. It was found that the sound attenuation is affected by the temperature ratio, the sound wavelength to characteristic length of the temperature gradient relationship as well as the shape of the temperature gradient.; In the two-dimensional study, the analysis was carried out using two different definitions of sound energy attenuation, global and local. Global sound energy attenuation is shown to depend on the thickness of the thermal barrier and the temperature ratio between the hot and cold zones, while local attenuation is in addition dependent upon the location of the interrogation point (the location where the sound level is determined). Hence, global sound energy attenuation is more appropriate for the systematic study while local attenuation is more appropriate for comparisons with experimental results. The total energy contained by the thermal field is also found to be an important parameter when all other parameters (temperature ratio, mean value of the gradient and characteristic length of the gradient) are kept constant. As a general conclusion, the thermal barrier can indeed cause significant sound attenuation and total internal reflection is possible. Finally, a method for the critical angle evaluation, when the thermal gradient is both finite and infinite, was developed and demonstrated.