| The oblique detonation engine is suitable for the breathing hypersonic propulsion system with higher flight Mach number than Scramjet.It not only has the advantages of Scramjet,but also realizes the high efficiency characteristics of detonation combustion mode.Its feasibility and superiority have been proved in early studies.The main fuel of aeroengine is hydrogen and jet fuel,and oblique detonation combustion process is directly related to the heat release of fuel.At present,the research on oblique detonation mostly uses hydrogen with rapid chemical reaction exothermic process as fuel,but the formation and characteristics of oblique detonation in hydrocarbon fuel with limited reaction rate are not well understood.In addition,the research on oblique detonation is still in the basic academic stage,such as the evolution of structural characteristics.The stabilization and standing mechanism of oblique detonation wave,the initiation and development process of oblique detonation,and the variation law of characteristic parameters of oblique detonation flow field with the change of incoming flow conditions are not well understood.Aiming at the above basic problems of oblique detonation,this paper firstly analyzes the standing mechanism and standing range of oblique detonation waves by using the theoretical analysis method with hydrogen as the fuel.On this basis,numerical simulation studies are carried out to reveal the initiation mechanism and development process of oblique detonation in hydrogen fuel,and obtain the characteristics variation of oblique detonation flow field under different incoming flow conditions.Finally,based on the above research ideas,nheptane,which is similar to jet fuel,is selected as fuel to explore the standing mechanism and flow field characteristics of oblique detonation in finite chemical reaction rate.The details are as follows:(1)According to the parameter relationship of flow field front and behind the oblique detonation wave,the variation law and internal mechanism of the standing range of oblique detonation wave in hydrogen under different incoming flow conditions are calculated and analyzed.The results show that under the conditions studied in this paper,in the hydrogen/oxygen/argon with equivalence ratio of 0.2 at environmental conditions and the inflow velocity of 2500 m/s,the standing range of oblique detonation increases by 47.5%compared with that under the condition of stoichiometric ratio,while the initial pressure and temperature of gas mixture have little influence on the standing range of oblique detonation wave.The stationary mechanism of hydrogen oblique detonation is explained,which is the basis of the research on the characteristics of oblique detonation.(2)Under the premise of satisfying the standing of oblique detonation wave,the flow field characteristics of oblique detonation in hydrogen are studied by numerical simulation method in view of the formation process of oblique detonation,the change law of main characteristic parameters of oblique detonation and the wave system morphology with the change of incoming flow conditions.The internal mechanism of the variation of the characteristics of the oblique detonation flow field and the temperature and pressurization performance of the combustion product flow field under different flow conditions are analyzed.The results show that,under the conditions studied in this paper,the smooth transition oblique detonation is more easily formed in the flow field when the equivalent ratio is less than 1.0,and the initiation length of oblique detonation reaches the minimum value when the equivalent ratio is about 0.8.In addition,the inhomogeneous distribution of the equivalence ratio of incoming fuel makes the initiation length of oblique detonation longer by more than 10%compared with that under the condition of homogeneous inflow.The variation law of the main characteristics of oblique detonation is obtained,which provides a reference for the variation of the characteristics of oblique detonation flow field with incoming flow conditions.(3)Based on the research background of aeroengine operating environment with high humidity,such as climbing and through cloud,the characteristics of hydrogen and water mist two-phase oblique detonation flow field are studied by numerical simulation,aiming at the abrupt transition type and smooth transition type oblique detonation flow field corresponding to different initiation mechanisms in hydrogen fuel.Under the condition that the mass of water vapor gradually increases,the interaction of wave system structure in the induction area of oblique detonation flow field is analyzed,and the variation rule of the morphological characteristics of oblique detonation is obtained.The influence of the physical and chemical effects of water mist on the flow field characteristics of oblique detonation is further studied.The results show that,under the conditions studied in this paper,with the increase of incoming water mist mass,the oblique detonation induction length in stoichiometric ratio is increased more than two times of equivalence ratio of 0.5,which is more sensitive to the change of incoming flow water mist mass.In addition,the physical effect of incoming water mist mainly affects the morphology of the oblique detonation flow field,and the chemical effect mainly changes the chemical structure and reaction process in the oblique detonation induction zone.The evolution law of oblique detonation flow field in two-phase hydrogen is obtained,which provides reference for the study of oblique detonation stability.(4)According to the research idea of hydrogen oblique detonation,the flow field characteristics of oblique detonation in n-heptane fuel with limited chemical reaction rate are studied.Firstly,based on the theoretical relation of the parameters of oblique detonation wave,the general variation law of induction time,induction length and standing range of the chemical reaction of oblique detonation under different incoming flow conditions is obtained.The formation process,initiation mechanism and main characteristics of flow field of smooth and abrupt transition type oblique detonation are studied on the premise of satisfying the stationary of oblique detonation wave.The quantitative relationship between the transition type and the chemical reaction characteristic parameters of oblique detonation is obtained.Finally,based on the study of the basic characteristics of the oblique detonation in gas-phase n-heptane,the flow field characteristics of the oblique detonation in gas-liquid two-phase nheptane fuel are studied.The dynamic unstable structure in the initiation zone of stationary oblique detonation is obtained.The quantitative criterion for distinguishing oblique detonation structure is put forward,which can provide reference for predicting oblique detonation morphology. |
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