环形通道内爆轰波的起爆机制

旋转爆轰发动机环形燃烧室和预爆轰管的设计是影响发动机点火性能的关键因素。为了获得环形燃烧室中的起爆机制，使用多帧短时开快门摄像法，研究了不同含量氩气稀释的乙炔-氧气爆轰波经直管道沿切向进入环形通道中的传播过程和模式，重点关注爆轰波的失效和重新起爆机制。通过分析胞格模式发现环形通道内爆轰波的传播模式可以分为亚临界、临界和超临界3种状态。环形通道内爆轰波在顺时针和逆时针方向同时传播，根据初始压力和环形管道宽度的不同，会出现完全熄爆模式、熄爆-重新起爆模式和完全不熄爆模式，对应亚临界、临界和超临界3种状态。3种状态在顺时针和逆时针方向出现的顺序并不一致，相比较而言逆时针方向更易熄爆。研究同时也发现重新起爆通过两种方式实现：一种是通过解耦爆轰波与内壁面的反射以及其后的横向爆轰波，另外一种是通过燃烧转爆轰。通过分析直管的临界管径发现，随着环形通道宽度的增大，对于高浓度或低浓度氩气稀释的乙炔-氧气爆轰波，其临界管径均趋近于经典衍射问题中不稳定爆轰波的临界管径。实验研究结论将为旋转爆轰发动机燃烧室和预爆轰管的结构设计提供技术支持。     

来流边界层效应下斜坡诱导的斜爆轰波

以超声速预混气中的斜爆轰波为研究对象,对其在来流边界层效应下的特性进行了实验研究.在马赫数为3的超声速预混风洞中,通过斜坡诱导产生了斜爆轰波.当来流的当量比较低时,预混气中产生的是化学反应锋面与激波面非耦合的激波诱导燃烧现象.此时边界层分离区中的化学反应放热将使分离区尺度显著增大,流场非定常性显著增强,激波位置剧烈振荡.当来流的当量比较高时,预混气将产生斜爆轰波.此时边界层分离区会影响到斜爆轰波起爆时的形态.在小尺度分离区下,斜爆轰波起爆时呈突跃结构(有横波);在中等尺度分离区下,流场固有的非定常性使斜爆轰波呈间歇突跃结构;在大尺度分离区下,斜爆轰波起爆则呈完全的平滑结构(无横波).     

爆轰波在弯管内传播过程数值分析

应用基元反应模型和频散可控耗散格式(DCD)对氢氧爆轰波在弯管内的传播过程进行了数值模拟.计算中氢氧混合物化学反应采用了8种组分20个反应方程式.在处理化学反应引起的刚性问题时采用了时间算子分裂的方法.计算结果表明,在弯管小曲率半径壁面附近,由于膨胀稀疏作用,爆轰波强度减弱,在局部出现前导激波与放热反应区的解藕以及二次起爆现象;在弯管大曲率半径壁面上爆轰波在马赫反射和正规反射之间相互转变,使爆轰波加强.弯管内的爆轰现象与弯管曲率半径有关.     

聚心火焰在共振腔作用下引发爆轰的数值研究

 基于带化学反应的二维轴对称Euler方程，利用带有Superbee限制函数的波传播算法，对共振腔中的氢气-空气预混气的聚心燃烧进行了数值模拟，讨论了共振腔不同抛物面对起爆的影响。数值结果表明，在开始阶段，燃烧诱导的激波在轴心、火焰和固壁的反射，使火焰失稳，随后共振腔中的抛物壁面上产生一定频率和强度的反射激波，不断穿越火焰，使火焰进一步失稳，加剧了燃烧速度，最终导致爆轰的形成。同时，火焰在与激波的作用过程中，形状扭曲变形，呈封闭端小敞口端大的扁平头部蘑菇云。共振腔抛物面的不同形状引起激波聚焦位置的变化，会影响激波和火焰的相互作用，使起爆提前或推迟，甚至不起爆。     

脉冲爆轰发动机热射流起爆机理数值分析

应用频散可控耗散差分格式,求解具有化学反应项的Euler方程,探讨了热射流起爆可燃混合气缩短DDT过程的物理机制.数值研究模拟了不同条件下的起爆过程,从氢氧链式反应出发详细分析了氢氧爆轰直接起爆的SWACER(能量释放而形成激波或压缩波的相干放大)机制的建立条件,讨论了热射流起爆存在超临界、临界和亚临界三种直接起爆机制.     

旋转爆轰流场的三维结构及其径向变化的数值研究

基于带化学反应的三维Euler方程,采用8组元和24个可逆化学反应的基元反应模型,对等当量比的气相氢气/氧气系统在圆环形燃烧室内的旋转爆轰进行了数值模拟。结果表明,子爆轰波、斜激波和滑移线组成了旋转爆轰波的基本三维结构。由于旋转爆轰燃烧室特殊的几何构型,即内壁的发散和外壁的收敛,使内壁面附近的爆轰强度要小于外壁面附近的爆轰强度,最终实现旋转爆轰波在燃烧室内的自持传播。     

多点起爆下药型罩表面压力分布规律研究

 为了掌握多点起爆下药型罩表面压力的分布规律以及起爆点参数对压力分布的影响,运用LS-DYNA 3D有限元软件,对多点起爆时爆轰波相互碰撞并作用于药型罩的过程进行数值仿真研究。仿真结果与实验结果吻合较好。研究结果表明：多点起爆时,爆轰波在起爆点的对称平面处发生碰撞,碰撞位置出现超压现象,导致作用于药型罩表面的爆轰载荷分布不均匀,爆轰波碰撞区域的压力高于非碰撞区域;随着起爆点间距的增大,爆轰波作用于药型罩顶部的压力逐渐增大,而边缘部位的压力则逐渐减小,当间距为50 mm时压力发生突降,即起爆点间距存在上限值;随着起爆点数的增加,药型罩表面微元的压力逐渐增大,但增加幅度逐渐减小,压力的总体分布规律相似。研究结果为带尾翼爆炸成形弹丸战斗部中起爆点参数等关键技术设计提供了理论依据。     

气相爆轰波在分叉管中传播现象的数值研究

数值研究气相爆轰波在分叉管中的传播现象.用二阶附加半隐龙格-库塔法和5阶WENO格式求解二维欧拉方程,用基元反应描述爆轰化学反应过程,得到了密度、压力、温度、典型组元质量分数场及数值胞格结构和爆轰波平均速度.结果表明:气相爆轰波在分叉管中传播,分叉口左尖点的稀疏波导致诱导激波后压力、温度急剧下降,诱导激波和化学反应区分离,爆轰波衰减为爆燃波(即爆轰熄灭).分离后的诱导激波在垂直支管右壁面反射,并导致二次起爆.畸变的诱导激波在水平和垂直支管中均发生马赫反射.分叉口上游均匀胞格区和分叉口附近大胞格区的边界不是直线,其起点通常位于分叉口左尖点上游或恰在左尖点.水平支管中马赫反射三波点迹线始于右尖点下游.分叉口左尖点附近的流场中出现了复杂的旋涡结构、未反应区及激波与旋涡作用.旋涡加速了未反应区的化学反应速率.反射激波与旋涡作用并使旋涡破碎.反射激波与未反应区作用,加速其反应消耗,并形成一个内嵌的射流.数值计算得到的波系演变和胞格结构与实验定性一致.     

隔板装药对偏心起爆效应的放大作用

带隔板的聚能装药可有效调整爆轰波形,提高射流的侵彻能力。偏心起爆会导致射流弯曲偏转和速度降低等现象,即偏心起爆效应。现实生产工艺中,聚能装药战斗部的起爆点和隔板的安装不易实现对称控制,基于此问题,应用LS-DYNA有限元软件和ALE算法讨论聚能战斗部中隔板对偏心起爆下产生射流的影响。经对比有无隔板的聚能装药在不同偏心起爆距离下产生射流的形态及速度分布,结果表明:有隔板的聚能装药对偏心起爆效应具有放大作用,且偏心距离越大,放大作用越明显。     

基于乙烯或氢气的吸气式旋转爆轰发动机实验

基于氢气的旋转爆轰发动机研究较多,而碳氢燃料与空气混合较为困难,导致基于乙烯的旋转爆轰发动机燃烧技术难度很高.使用宽视野范围的可视化燃烧室观察旋转爆轰波的研究在国内尚未开展.在同一燃烧室内进一步开展了乙烯或氢气的吸气式旋转爆轰实验,来流总温为283~284 K,燃烧室壁面有140°石英玻璃观察窗,便于观察旋转爆轰波运动过程.空筒燃烧室爆轰环腔外径为100 mm,轴向长度为151 mm.燃料通过150个直径0.8 mm圆柱孔进入燃烧室,空气通过喉部1 mm宽的收敛扩张环缝流入环腔.高速摄影和低高频压力传感器均验证了旋转爆轰波的存在和速度值.以氢气为燃料的旋转爆轰波速度最高可达理论值的101%,爆轰波增压效应可达40%左右,乙烯旋转爆轰波速度可达理论值的89%.旋转爆轰波结构容易发生变化,不规则.氢气旋转爆轰的维持对燃烧室的结构要求比碳氢燃料要低,比乙烯旋转爆轰波更加稳定.      

氢氧爆轰波在激波管中的成长机制研究

 针对气相爆轰波成长机制研究,采用压力传感器和高速摄影技术,测试了氢氧混合气体在点火后的火焰波、前驱冲击波以及爆轰波的成长变化过程,计算了冲击波过程参数和气体状态参数,分析了火焰加速机制。实验结果表明,APX-RS型高速摄影系统可用于拍摄气相爆轰波的成长历程;氢氧爆轰波的产生是由于湍流火焰和冲击波的相互正反馈作用,导致反应区内多处发生局部爆炸,爆炸波与冲击波相互耦合,最终成长为定常爆轰波。     

Detonation simulations in supersonic flow under circumstances of injection and mixing

The unsteady, reactive Navier-Stokes equations with a detailed chemical mechanism of 11 species and 27 steps were employed to simulate the mixing, flame acceleration and deflagration-to-detonation transition (DDT) triggered by transverse jet obstacles. Results show that multiple transverse jet obstacles ejecting into the chamber can be used to activate DDT. But the occurrence of DDT is tremendously difficult in a non-uniform supersonic mixture so that it required several groups of transverse jets with increasing stagnation pressure. The jets introduce flow turbulence and produce oblique and bow shock waves even in an inhomogeneous supersonic mixture. The DDT is enhanced by multiple explosion points that are generated by the intense shock wave focusing of the leading flame front. It is found that the partial detonation front decouples into shock and flame, which is mainly caused by the fuel deficiency, nevertheless the decoupled shock wave is strong enough to reignite the mixture to detonation conditions. The resulting transverse wave leads to further mixing and burning of the downstream non-equilibrium chemical reaction, resulting in a high combustion temperature and intense flow instabilities. Additionally, the longitudinal and transverse gradients of the non-uniform supersonic mixture induce highly dynamic behaviors with sudden propagation speed increase and detonation front instabilities.     

Combustion wave propagation and detonation initiation in the vicinity of closed-tube end walls

There are not many studies on DDT with no obstacles and the initiation of DDT near the end of a closed tube. Therefore in the present study we experimentally investigate the mechanism of the combustion wave transition to a detonation wave when there are no obstacles. In particular, we show that a local explosion near the tube wall is necessary for the initiation of a detonation. Parameters that we varied are the wall configuration, distance between the ignition point and the wall, and initial filling pressure. The combustion waves and the compression waves are visualized using the Schlieren optical system. From the results, we found it is necessary for the combustion wave to reach four walls so that the detonation could be initiated by the local explosion. In the conditions of the present experiment, we exhibited that the local explosion did not occur in the vicinity of a single wall and four orthogonal walls; instead, the local explosion occurred in a situation with five orthogonal walls. The time of the local explosion and the detonation initiation is 2.6 ± 1.1 and 2.0 ± 0.1 times the characteristic time for the combustion wave to propagate hemispherically from an ignitor and reach the four walls.     

以HMX为基的两种压装高密度炸药的燃烧转爆轰实验研究

 为研究以HMX为基的固体高能炸药的燃烧转爆轰性能,采用同轴电探针和压力传感器测试技术对常用的A、B两种压装高密度高能炸药开展燃烧转爆轰实验,研究装药组分和约束条件对压装高密度炸药燃烧转爆轰性能的影响。实验结果表明：这两种压装高密度炸药难以发生燃烧转爆轰;在强约束条件下（45号钢,内径25.4 mm、外径65 mm、长度600 mm）,A压装炸药（HMX质量分数为95%,密度为1.86 g/cm³）基本实现了燃烧转爆轰,爆轰诱导距离约为545 mm;在相同的实验条件下,A压装炸药比B压装炸药（HMX质量分数为87%,密度为1.84 g/cm³）更易于发生燃烧转爆轰,即A压装炸药的安定性相对较差。     

Gasdynamic characteristics of toroidal shock and detonation wave converging

The modified CCW relation is applied to analyzing the shock, detonation wave converging and the role of chemical reactions in the process. Results indicate that the shock wave is strengthened faster than the detonation wave in the converging at the same initial Mach number. Euler equations implemented with a detailed chemical reaction model are solved to simulate toroidal shock and detonation wave converging. Gasdynamic characteristics of the converging are investigated, including wave interaction patterns, observable discrepancies and physical phenomena behind them. By comparing wave diffractions, converging processes and pressure evolutions in the focusing area, the different effects of chemical reactions on diffracting and converging processes are discussed and the analytic conclusion is demonstrated through the observation of numerical simulations.     

Gasdynamic characteristics of toroidal shock and detonation wave converging

Shock wave focusing is a fundamental problem in the shock wave research and the instantaneous impulse of high temperature and pressure generated at the focal points has been applied recently in industrial and medical researches[1]. There are several methods to create shock wave focusing, among which the more commonly-used one is to make a planar shock wave reflect from a concave surface, such as the elliptical or parabolic re- flector. Toroidal shock wave focusing has been proposed and investi…     

铝粉-空气混合物爆燃转爆轰过程及爆轰波结构

 在长为32.4 m、内径为0.199 m的大型长直水平管道中,对铝粉-空气两相流的燃烧转爆轰（DDT）过程及爆轰波结构进行了实验研究。对铝粉-空气混合物弱点火条件下DDT过程不同阶段的特征进行了分析,实验结果显示混合物经历了缓慢反应压缩阶段、压缩波加速冲击波形成阶段、冲击反应过渡阶段、冲击反应向过压爆轰过渡阶段和爆轰阶段,得到了混合物各阶段的DDT参数,由此进一步分析了DDT浓度的上、下限。在1.4 m爆轰测试段的4个截面的环向上各均匀安装8个传感器,对爆轰波结果进行测试,并对铝粉-空气混合物爆轰波的单头结构进行了分析。     

Experimental characterization of detonation initiation modes in a confined chamber flush-mounted with small-diameter ignition tubes

This work reports the experimental characterization of detonation initiation modes in a confined chamber in respect to the different types of reacting waves generated in various small-diameter ignition tubes. Depending on the length of the tube and mixtures composition, four types of reacting waves can be generated and utilized to initiate detonation in the main chamber, namely the over-driven detonation ignition wave, CJ detonation ignition wave, high-speed deflagration ignition wave and deflagration ignition wave. Based on the mechanisms of detonation initiation in the main chamber, four initiation modes can be observed: the direct initiation, the local explosion initiation, and the fast and slow deflagration-to-detonation transition (DDT) initiation. By comparing the detonation initiation positions and flame-tip velocities, the first two modes show appreciably shorter initiation distances compared to the DDT modes. The over-driven detonation ignition wave is shown to yield a high probability of direct initiation, while contrary to expectation, the high-speed deflagration ignition wave exhibits superior initiation performance compared to the CJ detonation ignition wave. It is illustrated that the energy decay through diffraction and the effect of precursor shock wave reflection on the wall of the rectangular chamber are viable factors responsible for this observation. The deflagration ignition wave is also shown to be able to rapidly initiate the detonation near the inlet of the chamber, albeit with a lower success rate.     

On the mechanism of the deflagration-to-detonation transition in a hydrogen-oxygen mixture

The flame acceleration and the physical mechanism underlying the deflagration-to-detonation transition (DDT) have been studied experimentally, theoretically, and using a two-dimensional gasdynamic model for a hydrogen-oxygen gas mixture by taking into account the chain chemical reaction kinetics for eight components. A flame accelerating in a tube is shown to generate shock waves that are formed directly at the flame front just before DDT occurred, producing a layer of compressed gas adjacent to the flame front. A mixture with a density higher than that of the initial gas enters the flame front, is heated, and enters into reaction. As a result, a high-amplitude pressure peak is formed at the flame front. An increase in pressure and density at the leading edge of the flame front accelerates the chemical reaction, causing amplification of the compression wave and an exponentially rapid growth of the pressure peak, which “drags” the flame behind. A high-amplitude compression wave produces a strong shock immediately ahead of the reaction zone, generating a detonation wave. The theory and numerical simulations of the flame acceleration and the new physical mechanism of DDT are in complete agreement with the experimentally observed flame acceleration, shock formation, and DDT in a hydrogen-oxygen gas mixture.