Thermo-Acoustic Coupling Characteristics Research Of An Afterburner Model

When the heat disturbance coupled with pressure disturbance during the aero-engine afterburner operation, the low-frequency combustion oscillations occurred, and resul Ted in afterburner cylinder overheating, afterburner ratio decreasing and so on. Therefore, the low-frequency combustion oscillations were not allowed in the afterburner. The thermo-acoustic coupling phenomenon was the essence of the low frequency oscillation in the afterburner chamber, so in order to study the thermal acoustic coupling characteristics in afterburner, this paper had completed the following tasks:1. The model of an integrated afterburner was built for theoretical analysis and experimental research based on the analysis of the acoustic properties and aerothermodynamics characteristic and similar criteria. A steady-state velocity obtained by numerical simulating with this model. Compared with the result of the theoretical calculations, a new numerical model of the integrated afterburner was improved.2. The perturbation of flow field effected on pressure disturbance and acoustic characteristics was studied by a unsteady cold characteristics analysis with a numerical calculated through large eddy simulation. The results showed that a distinct phenomenon of vortex shedding formed in the stabilizer trailing edge, and the process of vortex formation and demise; it was found that a maximum pressure disturbance amplitude and sound pressure level amplitude grew in the recirculation zone of model afterburner, and decreased along with both direction of the inlet and outlet; The change law of amplitude of pressure disturbance and acoustic wave were similar. An perturbation with frequency and amplitude adjustable was imposed in afterburner inlet through an UDF program in the Fluent. A maximum acoustic amplitude was found on the perturbation with 20 k Pa amplitude and 200 Hz frequency, and the perturbation effect on the acoustic wave amplitude by frequency was greater than of amplitude. When the perturbation frequency approaches to the system natural frequency, the acoustic amplitude reaches the maximum, and far from the natural frequency the sound wave was weakening. The acoustic intensity would be restrained with the amplitude of the disturbance increasing.3. The perturbation of flow field effected on thermo-acoustic coupling characteristics was studied by a unsteady combustion characteristics analysis with a numerical calculation through large eddy simulation. The results show that a body fitted flame on the surface of stabilizator, and the flame shape was in agreement with the experimental results; the value of numerical pressure disturbance frequency was slightly higher than the experimentally measured; when the disturbance frequency was less than the natural frequency, acoustic amplitude and pressure disturbance amplitude was raised with the increase of the disturbance frequency; if the disturbance frequency was greater than the natural frequency of the system, acoustic amplitude and pressure fluctuation amplitude decreased with increase of perturbation frequency; when disturbance parameters was 40 kpa amplitude and 20 Hz frequency, the amplitude of pressure fluctuation and the temperature fluctuation reached the highest magnitude.4. Built an afterburner model thermo-acoustic coupling experiment bench and measurement systems. The study of different inlet velocity, fuel-air ratio, nozzle position on the influence of indoor pressure disturbance characteristics and heat release fluctuation characteristics of the afterburner model. The results showed that when the fuel-air ratio was constant, the intake velocity greater pressure and the heat release fluctuation amplitude were large. Increasing the fuel-air ratio can effectively increase the intensity of thermo-acoustic coupling, when the fuel-air ratio approximates the appropriate ratio the thermo-acoustic coupling strength decreased with the increase of the fuel-air ratio. The change of the position of the nozzle had a significant effect on the thermo-acoustic coupling strength. When the nozzle was 10 mm away from the stabilizer front, thermo-acoustic coupling amplitude was quite smaller compared with the other positions.