The criterion of the existence or inexistence of transverse shock wave at wedge supported oblique detonation wave

A simplified theoretic method and numerical simulations were carried out to investigate the characterization of propagation of transverse shock wave at wedge supported oblique detonation wave.After solution validation,a criterion which is associated with the ratio Φ （u 2 /u CJ） of existence or inexistence of the transverse shock wave at the region of the primary triple was deduced systematically by 38 cases.It is observed that for abrupt oblique shock wave （OSW）/oblique detonation wave （ODW） transition,a transverse shock wave is generated at the region of the primary triple when Φ 〈 1,however,such a transverse shock wave does not take place for the smooth OSW/ODW transition when Φ 〉 1.The parameter Φ can be expressed as the Mach number behind the ODW front for stable CJ detonation.When 0.9 〈 Φ 〈 1.0,the reflected shock wave can pass across the contact discontinuity and interact with transverse waves which are originating from the ODW front.When 0.8 〈 Φ 〈 0.9,the reflected shock wave can not pass across the contact discontinuity and only reflects at the contact discontinuity.The condition （0.8 〈 Φ 〈 0.9） agrees well with the ratio （D ave /D CJ） in the critical detonation.

Periodic oscillation and fine structure of wedge-induced oblique detonation waves

An oblique detonation wave for a Mach 7 inlet flow over a long enough wedge of 30 turning angle is simulated numerically using Euler equation and one-step rection model.The fifth-order WENO scheme is adopted to capture the shock wave.The numerical results show that with the compression of the wedge wall the detonation wave front structure is divided into three sections：the ZND model-like strcuture,single-sided triple point structure and dual-headed triple point strucuture.The first structure is the smooth straight,and the second has the characteristic of the triple points propagating dowanstream only with the same velocity,while the dual-headed triple point structure is very complicated.The detonation waves facing upstream and downstream propagate with different velocities,in which the periodic collisions of the triple points cause the oscillation of the detonation wave front.This oscillation process has temporal and spatial periodicity.In addition,the triple point trace are recorded to obtain different cell structures in three sections.

Accelerated initiation of oblique detonation induced by disturbance in detonative zone

In the real flow for high altitude,the initiation mechanism of the oblique detonation involves the coupling of complex wave structures and combustion waves,which may result in the phenomenon of extinction.The approach of stable initiation is one of the key factors that restricting the oblique detonation engine from theory to practice.The wave structure,initiation characteristics and characteristic parameters of the flow field are analyzed,the two-dimensional Euler equation considering the detailed chemical reactions of multi-component are solved.First,the approaches of blunt bump and transverse jet are combined used to shorten the detonation distance of the oblique detonation.Results show that these methods can promote the accelerated initiation of the oblique detonation effectively,and the detonation distance can be shortened more than 90%.There are two wave structures induced by the blunt bump:weak coupled and strong coupled,adding the transverse jet promotes the transition between these two wave structures.Then,the shape of the bump and the characteristic parameters of the transverse jet are optimized.The streamline-shape bump can eliminate the recirculation zone formed after the circle bump and the ellipse bump.The transverse jet will produce an oblique detonation wave at the front of the jet position,which changes the wave structure and initiation mode of the oblique detonation wave.It is expected to reveal the accelerated initiation mechanism of oblique detonation under the induction zone disturbance and complex flow environment,deepen the understanding of the detonation law of oblique detonation wave under real flow conditions,and provide a scientific basic for the development of the combustor of the oblique detonation engine.

受限空间中斜爆震波波系结构及其演化

为了研究真实发动机中受限空间内斜爆震波的宏观波系结构,采用欧拉方程结合详细反应机理的数值模拟方法,开展了受限空间的斜爆震波的数值模拟,分析了不同转折角下斜爆震波波系结构及其演化过程。结果表明,在上壁面转折处膨胀波的影响下,斜爆震波反射形成的马赫杆在前移过程中衰减,最终会在上扩张壁面附近形成高温回流区和低温三角区的稳定结构,三角区由转折处波系、回流区和下游斜爆震波组成。随转折角增大,最终在转折处点处依次形成激波、弱压缩波和膨胀波,与斜爆震波相交,交点下游的斜爆震波衰减,在末端出现解耦现象。

斜爆震燃烧与斜爆震发动机研究进展

发展更高性能的吸气式高超动力成为未来高超声速飞行器研制的重中之重。现有基于煤油燃料的超燃冲压发动机,主要以爆燃模式组织燃烧,在高来流马赫数(Ma≥8)条件下,将面临高来流总温带来的高温离解和化学非平衡效应所带来燃料的能量难以充分释放和利用的难题,相比之下,斜爆震组织燃烧更接近于等容燃烧,具有燃烧释热速率快、热循环效率高等优势,是一种可应用于高马赫数吸气式动力的理想燃烧模式。斜爆震发动机能够显著缩短燃烧室长度,减少释热面积,是高马赫数飞行器极具潜力的吸气式动力方案。其中,斜爆震发动机内流道各部件的匹配设计、燃料喷注-混合、斜爆震波的起爆与驻定等是斜爆震发动机研制的关键技术,是当前高超声速领域的研究热点。但由于其面临的高速、高总温总压的来流条件以及爆震波在流场中的强间断与高速传播特性等,现有试验与数值模拟研究手段难以开展精细的燃烧流动机制研究,进而限制了相关控制机理的揭示与高精度模型的建立,使得斜爆震发动机工程研制较为困难,当前研究仍存在许多值得探讨的地方,文章在综述的同时对下一步研究提出相关建议。

Investigation of hot jet on active control of oblique detonation waves

The hot jet injection is utilized to actively control the oblique detonation wave,such as initiating and stabilizing an oblique detonation wave at a desired position that is shorter than the length of induction zone,and adjust the height of the oblique detonation wave at the exit of combustor when the oblique detonation wave engine is working on off-design flight conditions.The fifth order Weighted Essentially Non-Oscillatory(WENO)scheme and a two-step reversible reaction mechanism of the stoichiometric H_2/Air are adopted in the simulations.With the help of hot jet injection,the transition from inert oblique shock wave to the oblique detonation wave immediately occurs near the position of hot jet injection,and consequently the length of combustor can be reduced.The angle of oblique detonation wave also decreases as the hot jet injection approaches the nose of wedge.Additionally,the height of the oblique detonation wave at the exit of combustor can be flexibly adjusted,and also depends on the injection position and the strength of the hot jet.If the velocity of the hot jet is too weak to directly trigger the overall oblique detonation wave at the position of injection,increasing the injection pressure will improve the strength of the hot jet and results in a successful transition.

Standing window of oblique detonation with pathological behaviour

Standing of an Oblique Detonation Wave(ODW)on a wedge within combustor is the prerequisite of thrust generation for ODW engine which is regarded as a novel and conceptual propulsion device with hypersonic flight Mach number.Usually a standing window of ODW is defined as the wedge angle ranged from the ODW detached angle from wedge(upper limit)to the angle that a Chapman-Jouguet(CJ)detonation occurs(lower limit).For pathological detonation cases,however,the CJ detonation cannot be achieved,and thus the lower limit of the standing window of ODW should be revisited.In present study,two types of reactions in hypersonic incoming flow that include the behavior of pathological detonation,that is,the single-step irreversible reaction with mole variation and the two-step irreversible reactions with exothermic process followed by endothermic process,have been used for studying standing behavior of ODW.The steady detonation polar analysis of ODW is carried out for both reaction systems.The results reveal that the reaction with more mole decrement and the reactions with stronger endothermic process show the pathological detonation feature and therefore modify the lower limit of standing window of ODW.Three equivalent parameters are proposed to quantitatively measure the standing window range of ODW from points of view of thermodynamics,Mach number of incoming flow and heat effect of reactions.It is found that the standing window of ODW is determined by the specific heat ratio,the overdrive degree of detonation and the endothermic level of the hypersonic incoming flow,regardless of whether the detonation is pathological or not.

Oblique detonation wave triggered by a double wedge in hypersonic flow

Pressure-gain combustion has gained attention for airbreathing ramjet engine applications owing to its better thermodynamic efficiency and fuel consumption rate. In contrast with traditional detonation induced by a single wedge, the present study considers oblique shock interactions attached to double wedges in a hypersonic combustible flow. The temperature/pressure increases sharply across the interaction zone that initiates an exothermic reaction, finally resulting in an Oblique Detonation Wave(ODW). Compared with the case for a single-wedge ODW, the double-wedge geometry has great potential to control the initiation of the ODW. As a tentative study, two-dimensional compressible Euler equations with a two-step induction-reaction kinetic model are used to solve the detonation dynamics triggered by a double wedge. The effects of the wedge angles and wedge corner locations on the initiation structures are investigated numerically.The results show an ODW complex comprising three Oblique Shock Waves(OSWs), an induction zone, a curved detonation front, and an unburned/low-temperature gas belt close to the surface of the second wedge. Both the increasing wedge angle and downstream wedge corner location lead to an abrupt OSW–ODW transition type, whereas the former corresponds to the shock–shock interaction and the later has a greater effect on the exothermic chemical process. Analysis of the shock polar and flow scale confirms that the OSW–ODW initiation structure mainly depends on the coupling of shocks and heat release in a confined initiation zone.

Initiation characteristics of oblique detonation waves from a finite wedge under argon dilution

In this paper,the flow field characteristics of Oblique Detonation Waves(ODWs)induced by a finite wedge under argon dilution are studied by solving the Euler equations with a detailed chemical model of hydrogen and air.First,the effects of the expansion waves,argon concentration,geometric parameters,and Mach number on the ODW are discussed.The results show that the changes of these parameters may make the oblique detonation not be initiated.Then,the ODW initiation criterion of the finite wedge is summarized,as the characteristic length of the induction zone LCand the characteristic length of the oblique wedge LWmeet the condition LC/LW<1,the initiation of the ODW occurs;otherwise,it does not occur.What’s more,the Constant Volume Combustion(CVC)theory is applied to study the characteristic length of induction zone.It is found that CVC theory is more suitable for the“smooth transition”type of ODW flow field,the theoretical and numerical characteristic length in induction regions are in good agreement.This work is of great significance for the design of oblique detonation engines for hypersonic vehicles.

斜爆震发动机研究进展与技术挑战

斜爆震发动机(Oblique detonation engine,ODE)采用驻定斜爆震波(Oblique detonation wave,ODW)实现高超声速气流中燃料化学能向推进系统机械能的高效转化,可大幅提升吸气式飞行速域上限,具有重要发展潜力和应用价值。本文从早、中、近期3个阶段概述ODE发展历程,总结当下斜爆震燃烧及发动机的研究现状。重点从发动机设计角度综述国内外在斜爆震燃烧组织、燃料喷注掺混以及总体性能与内流设计3方面的研究进展。深入分析了总体约束下的内外流一体化设计、高超声速气流中的燃料喷注掺混、复杂来流条件下的稳定燃烧组织、高热载荷防护以及超高速工况试验条件5大技术挑战及重点关注方向,为后续深入技术攻关及应用提供参考。

有限长度斜劈对燃烧室斜爆震波起爆结构影响研究

斜爆震发动机利用斜劈在超声速可燃混气中产生的斜爆震波实现快速高效的燃烧,在更高马赫数吸气推进领域极具应用潜力。面向斜爆震发动机工程应用,首先需要明确飞行条件下燃烧室内斜爆震波的起爆结构特征。但以往的研究大多采用无限长斜劈假设,不能真实反映实际燃烧室中有限长斜劈下的斜爆震燃烧特性。基于此,本文针对斜劈长度和斜劈后壁面倾斜角度两个关键设计参数,研究了在飞行马赫数8~10条件下,有限长度斜劈对斜爆震波起爆结构的影响。结果表明,对于不同高空飞行工况对应的不同起爆区结构斜爆震波,均存在一个临界斜劈长度,只有当斜劈长度缩短至临界斜劈长度时,斜爆震结构才会明显改变。相反,有限长度斜劈末端产生的膨胀波不会影响斜劈表面热释放和压缩波的汇聚过程,因此不会影响斜爆震波起爆结构。通过分析斜劈表面热释放过程,提出了一种理论的临界斜劈长度预测方法,其在不同飞行工况下的计算结果与仿真结果吻合较好。

环形燃烧室中圆台斜爆震燃烧特性研究

面向宽域爆震组合动力发展需求,首次提出适用于轴对称环形流道的圆台诱导斜爆震燃烧组织形式,通过数值模拟验证较低马赫数飞行工况下圆台诱导驻定斜爆震燃烧的可行性以及与斜劈、圆锥斜爆震燃烧的差异,从几何与来流参数两方面研究了圆台诱导斜爆震波的起爆与驻定特性。结果表明:在Ma7飞行工况,相比于圆锥和斜劈,环形燃烧室中圆台可以同时实现斜爆震波的加速起爆与稳定驻定。圆台上游的压缩作用以及下游的膨胀作用,使得圆台斜爆震波存在脱体而不前传的特殊起爆区结构。圆台内径、圆台角度、来流压缩程度以及当量比增大均有利于圆台诱导斜爆震波的起爆。同时,起爆区结构也会出现从渐变到突变再到稳定脱体的变化规律,相应的起爆距离逐渐缩短,爆震波角度逐渐增大。

高速弹丸诱导斜爆轰激波结构实验研究

斜爆轰推进系统在高超声速推进领域具有广阔的应用前景,其释热迅速、比冲高、燃烧室结构简单的优点吸引研究人员的持续关注.然而,斜爆轰的地面试验同时涉及到高速试验环境模拟、燃料与氧化剂混合、高温燃烧流场结构测量等技术难点,当前国内外系统的试验研究仍然十分有限,难以支撑斜爆轰发动机的研制.为了研究自持传播的斜爆轰激波结构与波面流动特性,基于爆轰驱动二级轻气炮开展了高速弹丸诱导斜爆轰实验研究,使用直径30 mm球头圆柱形弹丸发射进入充满氢/氧可燃混合气体的实验舱中以起爆斜爆轰波,并采用两种阴影技术对实验流动结构进行测量.实验中在不同速度、不同充气压力下观察到三种弹丸诱导激波结构,即激波诱导燃烧、弹丸起爆爆轰波和相对弹丸驻定的斜爆轰波,实验舱充气压力下降则会造成爆轰横波尺度增加与波面流动失稳.实验中,斜爆轰激波角与理论分析结果吻合较好,弹丸气动不稳定带来较大的弹丸攻角会对激波角测量带来一定偏差.通过对斜爆轰波波面法向传播速度的测量发现,随着远离弹丸,斜爆轰传播速度由弹丸飞行速度衰减至接近实验气体CJ速度,弹丸速度的降低会加速斜爆轰波传播速度的衰减.

斜爆轰波总压规律及其在爆轰发动机分析模型中的应用

爆轰推进系统具有热循环效率高和燃烧速率快等优点,逐渐展露出将取代传统动力技术的趋势,在高超声速飞行器推进领域中具有广阔应用前景.对推进系统而言,气流总压损失需要尽可能小,从全解域出发研究斜爆轰波总压特性有利于在爆轰推进系统的概念设计阶段控制总压损失量值.文章关注于已经形成稳定的斜爆轰波面,将斜爆轰波视为有瞬时能量添加的斜激波,利用极曲线方法研究斜爆轰波总压损失问题.以波前法向马赫数作为爆轰波强度表征量,推导出斜爆轰波强度关系式,发现绝热斜激波强度最弱关系式同样适用于斜爆轰波.借用激波图解法,证明了斜爆轰波最小总压损失特性仍然存在,并进一步揭示了最小总压损失线会随着添加能量的增大而向更大的爆轰角偏移,而原本对称的总压损失规律被打破.此外,还获得了增加能量大小和诱导爆轰楔面角度对最小总压损失的影响规律,发现当获得的能量越多而楔面角度越小时斜爆轰波总压损失极值点越容易向更大的爆轰角偏移.最后,根据斜爆轰波总压特性,提出了一种可提高发动机总压理论上限的简化设计思路,斜爆轰波总压规律可为斜爆轰发动机的概念设计提供参考.

膨胀波对斜劈稳定斜爆震波特性影响的数值研究

为探究燃烧室内可能存在的膨胀波对斜爆震稳定燃烧的影响,基于块结构自适应网格加密的AMROC程序,求解多组分可压缩化学反应流Euler方程,研究了膨胀波对斜劈诱导斜爆震流场的影响。发现无限长斜劈模型中,斜爆震波面角度是缓慢增加的,膨胀波影响下,斜爆震波面角度明显下降。从爆震波面角度变化中可以明显看出膨胀波的影响范围和爆震波的衰减程度。来流的低静压不会改变膨胀波影响范围,但容易导致爆震波衰减直至发生解耦,因此高马赫数低静压来流条件下斜爆震燃烧的稳定性和燃烧效率需要着重考虑。此外,使用普朗特-梅耶膨胀波基本原理对膨胀区进行分析,发现爆燃区流场参数与理论值吻合较好,且壁面附近前马赫线角度与近似膨胀波前沿较为接近;基于此,发展了一种定性评估斜劈末端膨胀波影响范围的手段,在膨胀波前马赫线角度基础上适当增加4°~10°,可以近似得到膨胀波的前沿位置。

非均匀来流中斜爆轰波对扰动的动态响应特性

在斜爆轰推进系统中,经过进气道压缩的气流速度仍然很大,导致斜爆轰波前的气流难以达到均匀预混,进而对斜爆轰波系产生影响。以高空飞行条件下非均匀来流中的斜爆轰波系为对象,采用Euler方程结合氢气-空气基元反应模型,通过波角变化和波面位置偏移研究了斜爆轰的受扰动特性。采用当量比作为非均匀的表征变量,在斜爆轰波面上游引入了一个高度可变的扰动区,定义φA为扰动幅值,扰动区的当量比分布通过正弦函数进行模化。研究发现,随着φA的减小,波角减小,波面向下游移动;随着φA的增大,波角增加,波面向上游移动。当φA为负值且足够小时,可以观察到波角突变的新现象,分析表明此现象源于来流当量比非均匀作用下的重新起爆。当φA为正值且足够大时,被扰动区的波角处于非平衡状态,较大的当量比梯度会导致其高于理论值,而较小的当量比梯度会导致其低于理论值。对波面位置的偏移量进行了量化分析,发现波面位移随φA的变化仅在其为正值时是非线性的,在其为负值时是线性的,随扰动区高度的变化也是线性的。

爆震发动机研究进展

爆震是实现增压燃烧的一种重要途径,得益于爆震循环的热效率增益,基于爆震构建的推进装置具有显著的理论性能优势,有希望推动航空航天动力技术的跨越发展。本文在总结经典爆震理论和爆震推进相关的基础科学问题进展的基础上,进一步介绍了连续旋转爆震发动机的低阶模型建立方法以及涡轮式和冲压式连续旋转爆震发动机性能分析等方面的研究进展,并概括了斜爆震发动机的性能分析和关键问题研究进展。最后基于当前研究基础提出对爆震发动机未来研究的展望。

爆轰波斜冲击金属介质理论在聚能装药药型罩设计中的应用研究

将爆轰波斜冲击金属介质理论引入聚能药型罩罩高参数设计中,运用LS-DYNA显式动力学软件对爆轰波斜入射铜介质进行了仿真计算,得到了接触位置压力峰值P与入射角φ0之间的关系,数值仿真结果和理论计算值、试验值均吻合得较好。基于仿真计算和理论分析,得出了圆锥形和球缺形药型罩点起爆条件下罩高参数确定的工程算法,并将其应用于一种组合式战斗部的设计中。该方法为药型罩高度的确定提供了基于理论分析方面的设计依据,丰富了聚能装药战斗部的设计方法。

超声速斜爆震发动机起爆过程研究综述

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