Study On Thermal-acoustic-structural Coupling In Combustion Chamber

In this paper,the basic theories of combustion,acoustics and vibration are introduced firstly,then the physical model and finite element model of flame,acoustics and structure are analyzed.The theoretical and experimental verification of the finite element model established in this paper is carried out.After that,the coupling theory is introduced,the thermo-acousto-solid coupling mechanism is analyzed,and the bidirectional coupling numerical model is established.In this paper,a single frequency sound wave is used for transient simulation research and analysis.The unstable combustion is simulated by setting the inlet condition as a pulsed inlet.The thermoacoustic-acoustic-mechanical coupling characteristics of the combustion chamber were analyzed by studying the variation law of internal parameters of the combustion chamber under different combustion conditions and the dynamic characteristics of the combustion chamber.The result shows that,it's feasible to simulate the acoustic transmission process by using CFD software,the calculation results are in good agreement with the theoretical calculation results.The average temperature in the combustion chamber increased by 15% and the acoustic pressure increased by 134.8% when the air-fuel ratio increased from 0.6 to 1.4,the frequency of acoustic pressure wave is constant.When the air-fuel ratio increases,the combustion is more unstable.Under the influence of thermoacoustic coupling,the acoustic pressure distribution at different locations within the combustion chamber is uneven,and the amplitude of the acoustic pressure near the outlet is significantly reduced,the decrease is about 75%.The combustion chamber stress wave is almost made up of five kinds of wave whose frequency are 1~5 times frequency of acoustic wave in combustion chamber,and the first kind of wave has bigger coherence with stress wave than others.The thermal stress is the same as the sound pressure stress level,and the influence of the two on the structure could not be neglected,and the acoustic stress is alternating stress,which could cause structural resonance.Areas of high thermal stress overlap with areas of higher sound pressure stress,and stress is greater at the corners of the wall,local stress concentrations in these areas can lead to the initiation and propagation of fatigue cracks.The response of the combustion chamber structure to the sound pressure is related to the excitation frequency of the sound pressure,when the excitation frequency is close to the natural frequency of the combustion chamber,the sound pressure stress will be significantly improved.