IMECH-IR  > 高温气体动力学国家重点实验室
复杂波系作用下的斜爆轰形成机理研究
Alternative TitleInvestigation of Oblique Detonation Initiation Mechanism under Complex Wave System
方宜申
Thesis Advisor姜宗林
2019-05-23
Degree Grantor中国科学院大学
Place of Conferral北京
Subtype博士
Degree Discipline流体力学
Keyword斜爆轰,起爆,波系结构,基元反应,数值模拟
Abstract

气相爆轰波是一种由激波诱导产生的超声速燃烧波。利用爆轰燃烧释放的能量从而产生推力的爆轰发动机,具有释热速率快、热循环效率高的特点,可望应用于亚声速、超声速和高超声速等各种推进系统。目前,三种爆轰发动机得到了广泛关注,分别是脉冲爆轰发动机、旋转爆轰发动机和斜爆轰发动机。作为一种应用于高超声速推进的发动机,斜爆轰发动机利用楔面压缩产生的斜激波诱导燃烧,兼具爆轰发动机和超燃冲压发动机的优点。然而,以前对斜爆轰的研究多集中在对简化、理想状态的分析讨论,主要针对均匀混合来流、半无限长楔面诱导起爆的情况,而对在发动机中斜爆轰燃烧面临的复杂、真实问题,如非均匀来流、燃料特性对波系结构的影响规律,波后复杂波系对燃烧产物的作用等问题的研究较少。本文面向工程需求,建立简化模型并开展数值模拟,在以下几个方面取得进展:

1、来流条件对斜爆轰波的影响,包括非均匀混合和不同燃料的影响。首先,考虑发动机中非均匀混合的必然性,通过控制化学反应当量比,建立了壁面附近来流混合不均匀的高空来流模型。通过数值模拟发现这种情况下,与均匀来流情况相比,反应面形状的存在很大差异。本研究定义了起爆特征长度和爆轰波面位置,并分析讨论上述两物理元素其随当量比的变化而改变的规律。结果显示起爆区长度变化曲线为典型的“U”型曲线,而爆轰波面位置在富燃条件下随当量比的变化基本不变。通过分析上述现象产生的原因,揭示了非均匀来流中的斜爆轰起爆机理。其次,采用基元反应模型,研究了另一种爆轰研究常用燃料,即氩气稀释的乙炔氧气混合气体中,斜爆轰波的波系结构特征和起爆机理。结合化学动力学计算,分析了氢气起爆与乙炔起爆的诱导区长度区别,讨论了马赫数和初始压力对诱导区长度的影响。结果表明,在大比例(大于70%)氩气稀释的乙炔燃料斜爆轰中,存在着化学释热与能量的竞争关系,进而导致了不同氩气稀释下的诱导区长度近似相等。

2、有限长楔面诱导的斜爆轰波系结构。鉴于真实飞行状态中,发动机内用于诱导产生爆轰的楔面不可能满足无限长的条件,建立了爆轰波后气流在转角作用下再次膨胀的流动模型,研究了稀疏波对斜爆轰波起爆区的影响。结果表明稀疏波的位置非常关键,如果该位置比较靠近下游,则对起爆的影响很小;而随着稀疏波的位置前移,将逐渐导致无法起爆。更重要的是,发现不同的起爆区结构,如平滑起爆和突变起爆,对稀疏波的响应规律不同,导致了不同的“近熄爆”动力学结构和过程。此外,还研究了粘性边界层对斜爆轰波的作用,发现在平滑过渡中边界层的影响可以忽略,而在突变过渡中起爆点的大幅前移。其机制在于后者有横向激波与边界层的相互作用,在边界形成回流区,导致放热反应以及边界层厚度变大。

3、超声气流中钝头体诱导的斜爆轰波起爆。为了实现高空来流条件下的可靠起爆,探索了采用钝头体诱导斜爆轰波的流场。对球体诱导斜爆轰波的研究中发现,存在临界直径,如球体直径小于该值,马赫数的增加只会使流场出现激波与燃烧带解耦的情况,不会起爆。另一方面,研究了钝楔起爆的情况,发现在成功起爆的条件下,比直接用楔面进行起爆可用飞行马赫数范围大。基于起爆理论开展计算,获得了临界起爆直径预测公式,结果与数值模拟符合较好。

Other Abstract

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.

Language中文
Document Type学位论文
Identifierhttp://dspace.imech.ac.cn/handle/311007/78941
Collection高温气体动力学国家重点实验室
Recommended Citation
GB/T 7714
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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