Simulation Study Of Self-Excited Oscillation Flow In Supersonic Combustor With Cavity

In this paper,Realizable k-epsilon numerical simulation method is used to simulate the supersonic combustion chamber with cavity to investigate the inducement of self-excited oscillation and characteristic of the supersonic cavity shear layer.The length to depth of the cavity was respectively changed to 2-6.The influence of cavity length to depth ratio on the self-excited oscillation is studied.The three-dimensional supersonic combustor model with rectangular concave cavity and herringbone cavity is simulated by Realizable k-epsilon and LES.The influence of herringbone cavity on combustion chamber flow field and self-excited oscillation is explored.The study shows that the fluctuation of the shear layer in the cavity of supersonic combustion chamber is the main inducement of the self-excited oscillation.The frequency of self-excited oscillations mainly depends on the length of the cavity,which is not related to the depth of the cavity.With the increase of the ratio of length to depth,oscillation frequency corresponding to the maximum sound pressure level increased gradually.As the cavity depth decreases,the frequency of each order gradually decreases.The ratio of the oscillation frequency of different cavity length is the reciprocal of the ratio of the cavity length,which is 1/L times the length of the cavity.The longer the cavity length is,the more compact the spectrum distribution is.The larger length to depth ratio of cavity（lower cavity depth）helps reduce the resistance and pressure loss of the combustion chamber.The spectrum distribution pattern of the same length to depth ratio is basically the same.The first four order frequencies of the cavity with length to depth ratio of 2 has frequency doubling relationship,that is f_n+1=2f_n The third frequency is the main frequency when the length to depth ratio is 3,4,6.While the second frequency as the main frequency when the length to depth ratio is 2 and 5.The first five order frequency of the self-excited oscillation satisfies the formula:f_n（10）3-f_n（28）f₃.Shear layer change is the principal cause of the self-excited oscillation frequency of the third order,the flow vortex development is the main cause of the sixth order frequency.Cavity shear layer movement,vortex flow and acoustic oscillation coupling each other causing self-excited oscillation phenomenon.