An Investigation On Flow Model And Combustion Characteristic Of Rearwall-Expansion Cavities In Supersonic Flows

The present study focused on the rearwall-expansion cavity in the conditions of combustion,and investigated the flow mode,the combustion mechanism,and other performance of the rearwall-expansion cavity.The study is a combination work of experiments and numerical simulations.Use the Fluent15.6 and the Navier-Stokes equation by averaging,combined with the engineering turbulence model to simulate the engine ignition and combustion in gaseous hydrogen,chemical kinetic model by the finite rate of global chemical reaction model,setting the same calculation and experimental conditions,to carry out research on the numerical simulation,and the simulation results and experimental results were comparative analyzed,verify the correctness and feasibility of the numerical simulation method.The numerical simulation of the different rear-wall height,different cavity length and different rearwall angle and different injection position,injection pressure under the condition of the rear-wall-expansion cavity in cold flow,transverse jet mixing flow and hydrogen combust-ion flow.According to the simulation results of test results and numerical analysis of different rear-wall height,cavity lengths,rear-wall angle and different injection position,injection pressure under the condition of the rear-wall cavity expansion in cold flow,transverse jet mixing hydrogen flow and the combustion flow field,summarizes the concave cavity configuration parameters and the influence of the hydrogen injection conditions on different flow characteristics.Found: front-wall height is a key factor to determine the characteristics of the rear-wall-expansion cavity,and expansion rate of the optimal expansion performance of cavity 40%;has a little influence on the change of cavity length and cavity aft wall angle on the combustion flow field,the optimum cavity length is 3~5 times the cavity before the depth of the wall.The best angle is 45°.The cavity injection mixing effect is better than the far cavity fuel injection,if the injection locations far away from the cavity,it will make the combustion zone down and weaken;the equivalent ratio of increase can significantly enhance the combustion effect,but will not change the combustion location of the reaction zone.Compared to the conventional cavity,sudden expansion channel of the rearwall-expansion cavity caused by faster combustion will produce high temperature and high pressure air heat release to the downstream channel,effectively alleviate the congestion caused by the heat release,so that the channel can add more heat energy at the same time,and reduce congestion.Furthermore,the flow stress can effectively reduce the flow resistance,then reduce the total pressure loss.This is the unique advantage of rearwall-expansion cavity.