The Numerical Study Of The Cold Flow Properties In The Trapped Vortex Combustor

Trapped vortex combustor (TVC), as a component of a ramgen engine, works at the condition of high pressure and velocity produced by the ramjet rotor. The characteristics of the combustor such as combustion stability, efficiency, fuel adaptability, and emission control are in urgent need of research. In order to understand in detail the geometry parameters, aerodynamic structure, and the flow field of the trapped vortex combustor will help to realize the ideas of flame stability. For the target of optimizing TVC's geometry structure and proceeding from the considerations of flame steady and utilizing vortices to stabilize flame, the different geometry structures and information of the flow field structure in TVC combustor are studied and analyzed this paper.Firstly, the steady method is used to study the optimum geometry structure and dimensions, the configuration of single bluff body in TVC, the effect of main flow velocity and bluff body width and the distance between the forebody and the afterbody with the condition of no air injection The structure of the forebody include? the shape of the head and the back of forebody, and the length at flow direction. The structure of the afterbody includes the shape, width, and the length. It is shown that the optimum flow structure could be gained when the width of the forebody is 67% of the width of the combustor, and such condition in the trapped vortex cavity is convincing to form a stable flow region. The optimum configuration of the bluff bodies is that the forebody has a round head, the length at flow direction is 50% of its width, and the back face of the forebody has a camber in the middle. The optimum configuration of the afterbody is a rectangular body with the width of 73% forebody's width, the length at flow direction is about 15-20mm, and the distance between the forebody and the afterbody is 60% of the forebody's width.The flow field of the trapped vortex cavity with air injection is also studied with steady method including the discussion of the injection position, nozzle size, velocity, angle and the equivalent width of the afterbody with air injection. The simulation results show that the optimum air injection position of the forebody is located at the middle of its back face, the optimum air injection position of the afterbody is located at the edge of the trapped vortex cavity close with the main flow, and the appropriate ratio of the air injection nozzle size is the diameter of the forebody's nozzle is three times than that of the afterbody. The air injection velocity of the forebody has more influence on the flow in the cavity. The favorable air injection angle is about 70°inward.Finally, the unsteady method is used to the flow properties of the trapped vortex cavity with or without the air injection. Through the numerical simulation, it is shown that there is a group of vortices in the rapped vortex cavity, and their stability and uniformity is strengthening with the air injection. The stabilization of the vortices in the trapped vortex cavity will create a good resident region and flow condition for the form and stabilization of flame in the combustion regime. The vortices between the cavity and the main flow could be hold when there is air injection. The two vortices located at the downstream of the afterbody keep steady without air injection, and keep once again steady after two periods breaking off from two vortices in basic steady condition.The deep study of the optimum structure and flow field in the trapped vortex cavity of the tranned vortex combustor with center bluff body established in the paper will lav a solid foundation in the research of the trapped vortex combustor in combustion condition and the practical application in the future.