Nonlinear Numerical Simulation And Experiment Study Of Rijke Tube Combustion Instability

Thermoacoustic instabilities are generated by a feedback interaction between combustion process and acoustic disturbances present in combustion systems.When unsteady heat is added in phase with the pressure oscillations,acoustical energy increases.The pressure waves propagate within the combustor and partially reflect from boundaries to arrive back at the combustion zone.And they may cause more unsteady heat release.Under certain conditions,this feedback can result in large and damaging self-excited thermoacoustic oscillations known as combustion instability.Such oscillations can cause structural dam-age,wearing at interfaces,flame flashback or blow-off,enhanced heat transfer and costly mission failure.To stabilize combustion systems,passive and active control approaches have been used to break the coupling between the unsteady heat release and acoustic waves.Compared with active control approaches,passive control approaches have such advantages as low cost and simple structure.Therefore they are widely used in many kinds of combustion system.The study of controlling Rijke tube combustion instability by electronic heater is conducted with the result of theoretical analysis in this work.It shows that flame-sustained pressure oscillations can be dramatically damped by increasing the surface temperature of heating bands.For more validation of the theoretical results,numerical simulation and experimental measurement are conducted respectively.Both the result have great agreement with the theoretical analysis,which indicates that it is feasible to control combustion instability with the second heat.As a comparison,but also for gaining insight on the feedback interaction between unsteady heat release and acoustic disturbances,experiment study is conducted to investigate the self-sustained thermoacoustic oscillations in a swirling combustor with cold water.The result shows that the amplitude of the thermoacoustic oscillation is obviously improved with the heat exchanger.It is a consistent process for the noise generated in the swirling combustion rising with the growth of equivalent ratio.Hence noise is reduced gradually first and then abruptly drop to the silence on the way back with the decrease of the equivalent ratio.The variation of pressure oscillation is different when the equivalent ratio changes in forward direction and reverse direction.When the equivalent changes in reverse direction,its average pressure oscillation is larger than in forward direction.The larger the inlet velocity is,more obvious the difference could be.The feature of acoustic velocity node in a standing wave could be used as another approach to stabilize the flame.The dynamic response of a jet diffusion flame to acoustic waves in a longitudinal tube is studied by numerical simulation in this work.It is shown that the jet and flame characteristics are highly sensitive to its axial location z,and the jet experiences large velocity fluctuations.Due to the large-amplitude acoustic disturbances,an interesting unsteady mushroom-shaped flame is observed.It is shown that the flame transfer function is nonlinear,and it depends strongly on not only the amplitude of the acoustic disturbances but also the frequency.It shows that the hydrogen combustion flame is not only more environmental than propane,but also more stable than propane,which is beneficial for combustion efficiency and combustion systems.