|Alternative Title||Investigation of Oblique Detonation Initiation Mechanism under Complex Wave System|
|Place of Conferral||北京|
Gaseous detonation is a shock-induced supersonic combustion wave. The detonation engine, which uses the energy released by detonation combustion to generate thrust, has the characteristics of fast heat release rate and high thermal cycle efficiency, and is expected to be applied to various propulsion systems such as subsonic, supersonic and hypersonic. At present, three kinds of detonation engines have received extensive attention, namely Pulse Detonation Engine ( PDE ), Rotary Detonation Engine ( RDE ) and Oblique Detonation Engine ( ODE ). As an engine used in hypersonic propulsion, oblique detonation engine uses oblique shock wave generated by wedge compression to induce combustion, which has the advantages of both detonation engine and scramjet engine. However, previous studies on oblique detonation focused on the analysis and discussion of simplified and ideal states, mainly concentrated upon uniform mixed inflow and semi-infinite wedge induced detonation. Nevertheless, there are few studies on the complex and real problems faced by oblique detonation combustion in engines, such as the influence of non-uniform inflow, fuel characteristics on the structure of wave system, and the effect of complex wave system on combustion products after wave. In this paper, facing the needs of engineering, simplified models are established and numerical simulation is carried out. Progress has been made in the following aspects.
1. The effects of incoming flow conditions on oblique detonation waves include non-uniform mixing and different fuels. Firstly, considering the inevitability of inhomogeneous mixing in the engine, a high-altitude inflow model with inhomogeneous mixing near the wall is established by controlling the chemical reaction equivalence ratio. The numerical simulation shows that the shape of the reaction surface is quite different from that of the uniform inflow. In this study, the detonation characteristic length and the position of detonation wave surface are defined, and the law of these two physical elements changing with the change of equivalent ratio is analyzed and discussed. The results show that the detonation zone length curve is a typical "U" curve, while the detonation wave surface position changes with the equivalence ratio under the condition of rich combustion. By analyzing the causes of the above phenomena, the mechanism of oblique detonation initiation in inhomogeneous inflow is revealed. Secondly, the wave structure and initiation mechanism of oblique detonation wave in a mixture of acetylene and oxygen diluted by argon are studied by using the elementary reaction model. Combining with chemical kinetics calculation, the difference of induced zone length between hydrogen initiation and acetylene initiation was analyzed, and the influence of Mach number and initial pressure on induced zone length was discussed. The results show that there is a competitive relationship between chemical heat release and energy in oblique detonation of acetylene fuel diluted by argon at a large proportion (more than 70%), which leads to the approximately equal length of the induced zone under different argon dilutions.
2. The oblique detonation wave system structure induced by a finite wedge. In view of the fact that the wedge used to induce detonation in the engine can not satisfy the condition of infinite length in real flight state, a flow model for the re-expansion of air flow after detonation wave under the action of rotation angle is established, and the effect of rarefaction wave on the initiation zone of oblique detonation wave is studied. The results show that the location of rarefaction wave is very important, if the location is close to the downstream, the impact on the initiation is very small, and as the position of rarefaction wave moves forward, it will gradually lead to the failure of initiation. More importantly, it is found that different structures of initiation zones, such as smooth initiation and sudden initiation, have different responses to rarefaction waves, resulting in different dynamic structures and processes of near extinction. In addition, the effect of viscous boundary layer on oblique detonation wave is also studied. It is found that the effect of viscous boundary layer on oblique detonation wave can be neglected in smooth transition, but the explosion point moves forward significantly in sudden transition. The mechanism lies in the interaction between transverse shock wave and boundary layer, which forms a reflux zone at the boundary, resulting in exothermic reaction and the increase of boundary layer thickness.
3. The oblique detonation wave induced by blunt body in the supersonic flow initiates. The flow field of oblique detonation wave induced by blunt body was explored in order to achieve reliable detonation at high altitude. In the study of oblique detonation wave induced by a sphere, it is found that there exists a critical diameter. If the diameter of the sphere is smaller than this value, the increase of Mach number will only cause the flow field to be decoupled from the combustion zone and will not initiate. On the other hand, the case of blunt wedge initiation is studied. It is found that under the condition of successful initiation, the range of flight Mach number available for initiation with blunt wedge is larger than that with direct wedge initiation. Based on the initiation theory, the critical initiation diameter prediction formula is obtained, and the results are in good agreement with the numerical simulation.
|方宜申. 复杂波系作用下的斜爆轰形成机理研究[D]. 北京. 中国科学院大学,2019.|
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