Numerical Study On Supersonic Combustion Characterisitics Of Hydrogen In The Combustor With Cavity

High-speed flight has always been a tireless pursuit of human beings.At present,the main engine of high-speed aircraft is supersonic combustion.However,due to the excessive speed of the fluid,the combustion process is complicated and the combustion efficiency is low.The fluid stays in the combustion chamber longer,which in turn can enhance combustion.In this paper,a simulation study of supersonic combustion is carried out on the combustion chamber with cavity.As a hot spot in recent years,the cavity structure can reduce the fluid velocity and enhance the combustion process in the combustion chamber.OpenFOAM was used to establish a solver suitable using PaSR combustion model and RANS methods for solving supersonic flow and combustion problems,and verified.Firstly,the supersonic flow/combustion of hydrogen in a single-cavity combustion chamber was simulated to analyze through the flow field,inlet conditions,cavity structure,and nozzle position.Under the flow condition,the backflow existed on the rear wall surface in the cavity,and the shock wave penetrated the boundary layer.Under combustion condition,the cavity was the main place of combustion and supersonic combustion has a delay.The combustion process runned from the boundary layer to the back wall of the cavity,and then to the extension and the interior of the cavity.The shock wave cannot penetrate the combustion boundary layer.The higher the hydrogen inlet temperature,the higher the combustion efficiency and total pressure recovery coefficient.The higher the air inlet temperature,the higher the total pressure recovery coefficient,but the lower the combustion efficiency.The inlet pressure of hydrogen and air did not have much effect on the flow field.The longer the cavity length?the deeper the cavity depth and the larger the cavity area,the higher the combustion efficiency.The total pressure recovery factor was mainly related to the length of the cavity.With a fixed cavity area,the combustion efficiency increased as the aspect ratio increased.Changing the inclination of the front / rear wall of the cavity had little effect on the combustion performance of the combustion chamber.Secondly,the supersonic flow/combustion of hydrogen in different types of double-cavity combustion chambers was simulated.The different double-cavity structures in this paper included tandem-cavity,parallel-cavity,and asymmetry-cavity.The second cavity of the tandem-cavity was the main combustion area,and the upper cavity of the parallel-cavity enhanced heat storage.The lower cavity of the asymmetry-cavity was still the main high-temperature area.As the distance of the upper cavity increased,the temperature decreased.The parallel-cavity has the lowest combustion efficiency and the total pressure recovery coefficient,followed by the asymmetry-cavity,and the tandem-cavity was the highest relatively.Finally,the combustion characteristics of the single-cavity and double-cavity combustion chamber were compared.The double-cavity structure can effectively improve the mixing efficiency of fuel and air,and the position of the cavity had effect on the growth rate of the mixing efficiency.At the same nozzle position and equivalent ratio,the cavity made the total pressure loss and the combustion efficiency of combustor higher;the larger the equivalent ratio,the lower the total pressure recovery coefficient and the combustion efficiency.The effects were similar when the nozzles on the same side,while the nozzles on the different side has a greater influence on the fluid.The nozzle and the cavity on the same side can achieve a better combustion effect.