Flame Stabilization And Propagation Characteristics Of Multi-cavity In Supersonic Flow

In this paper the supersonic combustion flowfield and the thermal experiment performances of multi-cavity flame holders were researched, the different configurations, such as: single cavity, parallel cavities and tandem cavities etc. were emphasized, and their performances were compared detailedly.Firstly, the theory of cavity flame stabilization in supersonic flow was stated, the influence factors related with the flame stabilization in single cavity configuration were analyzed, and the time scales under the lean burning and rich burn conditions were derived amply.Secondly, on the aspect of numerical simulation, by using the RANS simulation method the planar numerical simulation of the supersonic thermal experiments were carried out. The flow characteristics in the combustion chamber under different configurations were analyzed. It was found that on the front location of the jet in the supersonic combustion chamber the shock trains before jet exist. It compresses the supersonic inflow, increases the inflow pressure and temperature, and decreases its velocity. Due to the strike of the fuel spray jet to the back wall, the trailing edge shock waves occur on the back wall location of the cavity, which may continue to compress the flow passing through the cavity. In the tandem cavities, as the horizontal distance between the upstream and downstream is very far, the distribution of the shock waves are independent. Only the trailing edge shock waves in the upstream cavity and the shock waves before jet in the downstream of cavity intersect, forming the relative simple flowfiled. In the parallel cavities, because the length to depth ratio of the cavity is very big, the shock wave incidence to the shear layer after intersection, and at the same time the incidence shock waves change the recirculation zone of the cavity greatly, making the recirculation zone to be segmented, leading to the virtual recirculation zone to be shorten and the trailing edge shock waves of cavities to be changed. Later, the horizontal distance of the parallel cavities was increased in the experiments, the results showed that due to the variety of the shock wave intersection angle, the recirculation zone near the upstream of the cavity tends to be integrity.Finally, the experiment research corresponding to the condition of the above numerical simulation were done, and the former calculation results were validated by using the high speed photography and pressure scan technologies. With the help of the high speed photograph, it was clearly observed that the flame in the field was stabled in the shear layer and recirculation zone, which verified the former research of cavity flame stabilization theory. And synchronously in the course of the observation to the flame shape, it was found that the shock waves incidence to the shear layer after reflection and intersection, which leads to the flame to be extended along the shock wave incidence direction. Aimed at this phenomenon, the further observation was done, and the former judgement about the shock wave configurations in the cavity was proved partly. Moreover, by analyzing the data collected by the pressure scanner valve it was testified that under the conditions of the small equivalence ratio, compared with the different side configuration of the tandem cavities, the same side configuration will be better to the utilization of the upstream cavity for the downstream cavity. In the experiments of the parallel cavities, it could be seen that compared with the single cavity configuration, the wall pressure in the parallel cavities increase suddenly. Through the numerical simulation pictures, it could also be concluded that the strong shock wave after intersection occur near the shear layer, at this time the use of the jet pressure should be pay more attention, and the overlarge pressure should be avoided.