چكيده به لاتين
It is more than two centuries that the combustion equipments have been exposed to combustion instabilities. Entropy waves as one of the potentially effective sources to motivate this phenomena, found in 70s. These waves are hotter spots in the flow, convected by the flow inertia. A little studies have been carried out until early current century. Proving the crucial role of entropy waves in provoking combustion instability and transmitted noise in aero-combustors leads to raising focusing on them. Ignoring the effect of flow field on the entropy waves, however, is the main defect of the current literature, which causes some inconsistencies. Flow hydrodynamics may remain a wide spectrum of change in the entropy waves, which may lead to minor dissipation, dispersion or hard survival of the entropy waves. The points in the literature, which indicate either complete survival or attenuation, cannot guarantee the realities in the combustors. This defect causes a flawed prediction for combustion instability and transmitted noise. This dissertation is accordingly devoted on the entropy wave changes in a channel. The effects of hydrodynamic parameters and thermal boundary conditions on entropy wave changes are investigated numerically and experimentally. To study the wave change quantitatively, some novel functions are firstly introduced. Furthermore, the validity of assumptions used in the previous analytical studies is investigated and it is shown that some of them have a tight validity region. The effects of entropy waves on the flow field is firstly studied and it is shown that these effect may be significant, unlike the current claims. A correlation between the wave amplitude and the governing parameters is computed according to the experiments. In the analytical work of the current study, the amplitude and the phase of a convergent-divergent nozzle response to an entropy waves, affected by the flow hydrodynamics and thermal conditions is obtained. The wave change in a nozzle due to stretching is computed for the first time.
