Research On The Inducing Factors Of Afterburner Oscillating Combustion

The oscillating combustion is self-oscillation phenomenon generated due to the combustionchamber of the combustion processes and systems with the internal sound pressure fluctuationsintercoupling.The oscillating combustion has a great impact on the performance of the propulsionsystem structure, and it may even causes engine flameout,damage and destruction of the systemcomponents. In this paper, both methods of numerical simulation and experimental study are used tomake a preliminary study of vortex shedding and oscillation combustion mechanism, to explore theacoustic characteristics of oscillating combustion.A simple analysis of the acoustic characteristics ofthe combustion chamber, the numerical simulation of vortex shedding process stabilizer, andoscillating combustion process.Specific research work carried out in this article are as follows:1.Designed a simplified model of the afterburner, and analyzed acoustic characteristics of thecombustion chamber from the principle, calculated open at both ends, closed at both ends, and oneopen end closed at one end to the three acoustic structure of the first order to third order acousticnatural frequency.2.Numerical Simulation of the flow field after flameholder is performed,and found that there arethe structure of Vortex Street. The alternating periods of the vortex generation, development, growthand shedding on both sides of flameholder, and it is a period of the motion of vortex.The calculationshows that the changes of intake pressure pulsation and changing the size of the intake pressurepulsation are able to impact the process of vortex shedding. Additional,flameholder obstruction ratiodifferent from,the reae of the vortex shedding frequency and stability will be different.3.The pressure pulsation signal before and after the flameholder is measured by experiments. Thetest results are able to demonstrate an impact on the fluctuating pressure which occur after theflameholder,by changing the speed of intake and the structure of the flameholder. And get thefollowing conclusions:(1) The perturbations of air intake at the front of the flameholder could drivethe pressure pulsation at the same frequency.(2) In the test, the pulsation frequency supplied by thefan could drive the pressure pulsations after the flameholder, so we should try to weaken the influenceof the fan.4.Numerical Simulation of the unsteady combustion in model combustion chamber are performed.and fome the cloud images, we could found that the flame surface in the process of oscillatingcombustion occurs periodically jitter, and the oscillation frequency is consistent with the fvortexshedding frequency. By analyzing,it is also proved that the periodic shedding of vortices in the combustion chamber is capable of driving exothermic pulsation, and the exothermic pulsation willcoupled with the sound pressure pulsation, thus affecting the vortex shedding. These three processesconstitute the feedback process of the oscillation combustion, thereby inducing self-oscillation of thecombustion process in the combustion chamber.