| Combustion instability of the afterburner can be affected by various factors. The key factor is the instability caused by the interaction of acoustic, vortex and flame. Based on a certain type of aeroengine as the object of study, the research on the interaction of acoustic, vortex and flame has been carried out by the numerical simulation in this paper. The main contents and conclusions are as follows:1.Simplify the afterburner model and verify the correctness of the calculation method.According to the similarity criterion of Mach number in front of the flame holder, the afterburner is simplified based on its geometric structure characteristics. The same calculation method in this paper is used to simulate the model afterburner thermo-acoustic coupling characteristics, and the results are compared with experimental results. The calculation error is less than 10%.2.Cold flow field characteristics of the afterburner is studied. First, Vortex shedding process and the effect of vortex shedding on the dynamic pressure fluctuation of flow field is analyzed by the unsteady calculation method. Seacond, a varying acoustic wave disturbance is imposed on the inlet to observe the influence on the pressure fluctuation at different positions and vortex shedding frequency in the afterburner. The interaction of acoustic and vortex includes: 1)When the inlet conditions are changed, the frequency of vortex shedding changes, and is the same as the lift fluctuation frequency of the flame holder and the pressure fluctuation frequency of the vortex core. 2)When the vortex is shedding, the amplitude of the pressure fluctuation reaches the maximum in the recirculation zone,which accounts for 1.3% of the inlet total pressure. 3)With the increase of the frequency of the acoustic disturbance, the vortex shedding frequency and the pressure fluctuation frequency increase firstly, reaching the peak value at 20 Hz and then decrease. The amplitude of pressure fluctuation decreases firstly, reaching a minimum at 20 Hz and then increases. The pressure fluctuation caused by the vortex shedding is most sensitive to low-frequency disturbance. 4)With the increase of the amplitude of the acoustic disturbance, the vortex shedding frequency and the pressure fluctuation frequency increase, while amplitude of the pressure fluctuation decreases.3.The combustion characteristics of the afterburner is studied. Based on the calculation of cold flow field in the afterburner, the interaction characteristics between acoustic, vortex and flame is studied with 12 species and 10 steps chemical reaction mechanism. The parameters of equivalence ratio, inlet flow velocity, nozzle position and external acoustic disturbance on the inlet are varied. Theconclusions are drawn as follows: 1) With the periodic vortex shedding from the flame holder, the flame structure behind the flame holder presents regular periodic fluctuation, and the frequencies are the same; 2)When the equivalence ratio, inlet velocity and location of nozzle change, the frequencies of the vortex shedding, pressure and heat release fluctuations show the same variation tendency;3)The amplitudes of pressure fluctuation and heat release rate will increase firstly as the equivalence ratio increases, but when the equivalence ratio exceeds a critical value, the amplitudes will decrease.When the inlet velocity increases, the frequencies of the pressure fluctuation and heat release rate increase to a maximum and then decrease, while the amplitudes decreases initially and then increases.When the nozzles move towards flame holder, the frequencies of pressure fluctuation and heat release rate decrease, but the amplitudes will increase constantly; 4)The distribution of the amplitude of the pressure fluctuation along the axial are in accord with the distribution in the afterburner acoustic channel. The afterburner is most sensitive to low-frequency acoustic disturbance, and the energy of the acoustic field in thermal state is much lager than that in cold state. |
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