This paper investigates the hydrodynamic and heat transfer effects upon the dissipation and dispersion of entropy waves in non-reactive flows. These waves, as advected density inhomogeneities downstream of unsteady flames, may decay partially or totally before reaching the exit nozzle, where they are converted into sound. Attenuation of entropy waves dominates the significance of the subsequent acoustic noise generation.Yet, the extent of this decay process is currently a matter of contention and the pertinent mechanisms are still largely unexplored. To resolve this issue, a numerical study is carried out by compressible large eddy simulation (LES) of the wave advection in a channel subject to convective and adiabatic thermal boundary conditions. The dispersion, dissipation and spatial correlation of the wave are evaluated by post-processing of the numerical results. This includes application of the classical coherence function as well as development of nonlinear quantitative measures of wave dissipation and dispersion. The analyses reveal that the high frequency components of the entropy wave are always strongly damped. The survival of the low frequency components heavily depends upon the turbulence intensity and thermal boundary conditions of the channel. In general, high turbulence intensities and particularly heat transfer intensify the decay and destruction of the spatial coherence of entropy waves. In some cases, they can even result in the complete annihilation of the wave. The current work can therefore resolve the controversies arising over the previous studies of entropy waves with different thermal boundary conditions.

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A numerical investigation war carried ouf to predict and compare the fluid /tow and heat tmnsfer characteristics of two-dimenswnal turbulent confined impinging and opposing jet jlows. Five low-Rtyoldr-number k-E models and the standard high-ReynoI&-number model were used in the simulntion. The newly proposed Yap correction war also tested with low-Reyno&-number models in order to investigate its effect on the heat tmnsferpredierions for the impinging jet case. It war found that in some modek Pis correction improves the heal transfer predictions. A comparison is made between the simulation resub and the auailable erperimental dnfn forfluidflow and heat tmnsfer for a single slot jef impinging on a JW plnte and for flow in the opposing jet care. A paramem'c sfudy b made for flow and heal transfer chnracterinics in thc opposing jet configuration.

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