With the growing awareness of pollutant emissions from aero-engine combustor, fuel atomization system has been studied extensively. Fuel spray spatial distribution, droplet size, as well as fuel/air mixing play important roles in improving combustion performance. Air blast atomizer is one kind of the systems used in aero-engine combustors which involves shear driven pre-filming atomization. It creates a thin film of fuel along a solid surface, and then subjecting that film to shear from high-velocity air flow to achieve a secondary atomization. In this process, the spray wall interaction and hydrodynamic of the film formed on the filmer wall accelerate the atomization and the mixture of fuel and air, and also directly impact the later pre-filming atomization. For this reason, various researchers have studied the spray-wall interaction and the droplet formation after the impingement in the presence of a cross flow. In this paper, we use two spray-wall interaction models to simulate experiments performed by us. In the experiment, liquid jet was injected from a plain nozzle placed at the top of a wind tunnel, and droplets were shed from the jet surface due to primary atomization in the presence of high shearing cross flowing air. Fuel droplets then hit the wall to form a film, while secondary droplets were splashed. This process is simulated under different air flow velocities and jet fuel flow rates to evaluate the models' prediction accuracy. The assessment is done by comparing the droplet sizes and film thickness downstream of the tunnel. The calculated results show in general reasonable agreement with the measurement data.
In order to analyze the thermo-acoustic instability in combustion chamber, an unsteady heat release rate model is established, which is based on the linear analysis of chemical reaction kinetics. In this model, the fluctuation of heat release rate is determined by the fluctuation of fuel mass fraction, density, temperature and pressure, and influenced by both the convection of flow and propagation of acoustic wave. To verify this model, the unsteady heat release rate of premixed swirling flame and staged flame are calculated respectively, and compared with the experimental data. It is demonstrated that the transport velocity is the key parameter affecting the heat release rate fluctuation. Subsequently, the heat release rate model is employed to analyse the thermoacoustic instability of the annular combustor. The growth rate of the characteristic frequency of the combustor is obtained by analytically solving multi-dimensional acoustic wave equation in the frequency domain. The solution is used as the basis for determination of the self-excited thermoacoustic instability of the combustor. The results predicted by this model are compared with the results obtained by high fidelity numerical method such as large-eddy simulation. The comparison show that three types of self-excited oscillation frequencies corresponding to the first-order circumferential, first-order longitudinal and first-order circumferential and longitudinal mixed modes of the combustor, can be properly predicted by this model.
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