Study Of Methane-Air Rotating Detonation Propagation Characteristics And Flow Field Organization At Combustor Outlet

Improving cycle thermal efficiency has always been one of the research focuses and hotspots in the field of gas turbine technology.However,with the development of gas turbine related technologies becoming more and more mature,the efficiency of the compressor and turbine is close to the limit,and it becomes very difficult to further improve the cycle thermal efficiency of gas turbine.Based on its advantages of small entropy increase and selfpressurization,rotating detonation combustor is expected to significantly improve the thermal efficiency of the gas turbine cycle.However,there is still a lot of research to be done before the practical application of gas turbines based on rotating detonation technology.Among them,the study of rotating detonation formation and propagation characteristics is particularly critical,it involves the self-sustaining propagation and pressurized mechanism of detonation,which is a fundamental issue in rotating detonation technology and the prerequisites for the study of rotating detonation combustor performance.In addition,the combustor needs to be coupled with the downstream components to achieve power output,so the study of how to effectively organize the combustor outlet flow field based on stable detonation propagation is of great significance to promote the progressive development of detonation combustion technology to practical applications.Methane is one of the main fuels for gas turbine,which is chemically stable,easy to store and transport,while air is the most readily available oxidant,and the study of methane-air rotary explosion has engineering value.In this paper,for the above critical issues,methane-air is used as the research object,and numerical simulations are used to systematically study the formation and propagation characteristics of rotating detonation,the performance of rotating detonation combustor and the outlet flow field organization.The study investigates the formation process and detonation cell size change mechanism,reveals the mechanism of detonation stable self-sustaining propagation and pressurized performance of rotating detonation combustor,obtains the combustion chamber performance and flow field parameters under different incoming flow and back pressure conditions,and demonstrates the method of combustor outlet flow field organization.The main work is as follows:(1)Aiming at the problems of detonation formation and propagation characteristics,the variation law of methane-air cell size under the influence of initial pressure,initial temperature and equivalence ratio is calculated and obtained based on the cell formation mechanism,and the basic structural characteristics of methane-air detonation wave and the formation and propagation process are analyzed.Through the systematic analysis of the detonation combustion field in the stable propagation stage,the self-sustained propagation mechanism of detonation is revealed.The results show that the self-sustained propagation of detonation is related to the dynamic coupling relationship between the post-wave pressure,premixed gas filling and detonation wave height,and further reveals the pressurized mechanism of detonation combustor by analyzing the parameters variation along the typical traces of the working mass in rotating coordinate system.(2)In order to explore the impact of combustor structure size on the stable propagation of rotating detonation,this paper provides a detailed comparison of detonation wave structure and flow field distribution differences for combustor of different axial length and radial depth sizes.The calculation results show that the too short combustor axial length will limit the development of detonation wave,the too long one will make small disturbance waves in the flow field;the too small combustor radial depth will compress the radial wave,the too large one will make the detonation wave lateral expansion,resulting in flow loss.(3)Aiming at the problem of rotating detonation combustor performance,on the basis of verifying the reasonableness of combustor structural dimensions and cell size,this paper carried out a numerical study of rotating detonation combustor with different inlet pressure,inlet temperature,inlet gas equivalent ratio and outlet back pressure,and obtained the combustor pressurized performance and the flow field parameters change law under different initial conditions.The results show that the combustor pressurized ratio,detonation wave velocity,maximum chemical reaction rate and average axial velocity of the mass is positively correlated with the inlet pressure and negatively correlated with the inlet temperature,and reach maximum at equivalence ratio of 1,and the low equivalence ratio will lead to the decoupling of detonation wave.During the stable operation of detonation wave,the outlet back pressure basically does not affect the combustor pressurized performance,but the increase of back pressure will cause changes in flow field parameters.The initial conditions do not affect the total pressure pulsation law of detonation flow field.(4)Aiming at the problem of the outlet flow field organize of rotating detonation combustor,an outlet reformulation method is proposed in this paper,and the formation and propagation of detonation,combustor performance and outlet flow field parameters under different reformulation structures and reformulation angles are carefully analyzed.The results show that the reformulated structure does not affect the formation and propagation process of detonation wave,but it will lead to a delay in the formation of stable detonation wave.Within the scope of this paper,the two modified structures can effectively suppress the flow field parameter pulsation and improve the outlet parameter inhomogeneity while retaining a certain pressurized performance.For the unidirectional modification,when the expandable angle is changed from 0° to 45°,the peak outlet static pressure and static temperature are reduced by88.32% and 32.12%,respectively,and the outlet static pressure and static temperature inhomogeneity are reduced by 83.28% and 14.05%,respectively;for the bidirectional modification,the peak outlet static pressure and static temperature are reduced by 91.33% and33.25%,respectively,and the outlet static pressure and static temperature inhomogeneity are reduced by 90.51% and 22.63% respectively.