Hydrodynamic instabilities and transverse waves in propagation mechanism of gaseous detonations

The present study examines the role of transverse waves and hydrodynamic instabilities mainly, Richtmyer–Meshkov instability (RMI) and Kelvin–Helmholtz instability (KHI) in detonation structure using two-dimensional high-resolution numerical simulations of Euler equations. To compare the numerical results with those of experiments, Navier–Stokes simulations are also performed by utilizing the effect of diffusion in highly irregular detonations. Results for both moderate and low activation energy mixtures reveal that upon collision of two triple points a pair of forward and backward facing jets is formed. As the jets spread, they undergo Richtmyer–Meshkov instability. The drastic growth of the forward jet found to have profound role in re-acceleration of the detonation wave at the end of a detonation cell cycle. For irregular detonations, the transverse waves found to have substantial role in propagation mechanism of such detonations. In regular detonations, the lead shock ignites all the gases passing through it, hence, the transverse waves and hydrodynamic instabilities do not play crucial role in propagation mechanism of such regular detonations. In comparison with previous numerical simulations present simulation using single-step kinetics shows a distinct keystone-shaped region at the end of the detonation cell.     

Initiation of spherical detonation in hydrocarbon/air mixtures

Spherical detonations have been initiated by solid explosive (Tetryl) charges in well-mixed stoicheiometric air mixtures with each of the hydrocarbons, ethane, propane, n-butane, isobutane and ethylene at atmospheric pressure. Prior to initiation, the gases were contained in plastic bags; total gas volume and available path length were up to 1.6 m³ and 2 m, respectively. The detonations were shown to be self-sustained by continuous measurement of detonation velocity using X-band microwave interferometry. Measured detonation velocities were in all cases close to calculated C-J values.In a few experiments close to the limits of detonability, velocity and blast pressure/time records indicated that the propagating wave system is sometimes irregular. The irregularity that occurs just after initiation is characterised by a reaction front velocity very much lower than the constant detonation velocity, but subsequently attaining the latter by an acceleration process. These observations indicate the existence of a dissociated phase in which shock and reaction fronts may no longer be coupled.Because similar experimental conditions were used throughout, it was possible to establish the relative susceptibilities of the various fuel gases to detonation. Comparison is made with the Zeldovich criterion and a detonation kernel theory of Lee.     

Photochemical initiation of gaseous detonations

Direct initiation of detonations in gaseous mixtures of C₂H₂-O₂, H₂-O₂ and H₂-Cl₂ in the pressure range of 10–150 torr using flash photolysis was studied. Similar to blast initiation using a concentrated powerful energy source, it was found that for photochemical initiation, there exists a certain threshold of flash intensity and energy for each mixture at any given initial pressure and composition below which a deflagration is formed. At the critical threshold, however, a fully developed detonation is rapidly formed in the immediate vicinity of the window of incident UV radiation. However, at super critical flash energies, the amplitude of the detonation formed decreases and combustion of the entire irradiated volume approaches a constant volume explosion. It was found that photo-chemical initiation requires both a certain minimum peak value of the free radical concentration generated by the photo-dissociation as well as an appropriate gradient of this free radical distribution. The minimum peak radical concentration permits rapid reaction rates for the generation of strong pressure waves, while the gradient is necessary for the amplification of the shock waves to a detonation. If the gradient is absent and the free radicals are uniformly distributed in the mixture, then the entire volume simply explodes as in a constant volume process. The present study reveals that the mechanism of photochemical initiation is one of proper temporal synchronization of the chemical energy release to the shock wave as it propagates through the mixture. In analogy to the LASER, the term SWACER is introduced to represent this mechanism of Shock Wave Amplication by Coherent Energy Release. There are strong indications that this SWACER mechanism is universal and plays the main role in the formation of detonations whenever a powerful concentrated external source is not used to generate a strong shock wave in the explosive.     

Shock waves in water foams

Propagation of shock waves in tubes filled with water foams is studied using pressure gauges. Low amplitude shock waves consist of a precursor which propagates at a velocity slightly less than the acoustic velocity in the gas, and of a main compression wave which propagates slower than the precursor. Stronger shock waves have a single front. Maximum pressure rise in the incident and reflected shock waves cannot be calculated using one-dimensional conservation equations at the shock front. It is suggested that the flow of the liquid in foam cells has to be taken into account in order to predict the behavior of shock waves in foams. The nature of the gas which fills the cells is shown to have a strong effect on the quenching of blast waves in foams.     

电子束辐照下铝合金靶中热击波传播规律研究

文章研究了电子束辐照下铝合金靶中热击波的传播与衰减规律。首先给出了基于半径回归法的铝合金本构模型,并给出了将其应用于数值模拟的计算流程。然后,利用该模型以及自主编写的计算软件DRAM1D,模拟了脉冲电子束辐照铝合金的热击波效应。将计算结果与采用理想弹塑性本构模型得到的结果以及实验结果进行了比较,结果表明,相比于理想弹塑性本构模型,基于半径回归法的铝合金本构模型所得到的热击波衰减相对较快,与电子束辐照铝合金的实验结果符合较好,更适合于描述铝合金靶材中的热击波传播。     

Rankine涡作用下激波变形和分叉的数值研究

数值模拟了激波和Rankine涡相互作用，重点研究了波涡相互作用引起的激波结构的变化过程。应用非结构化适应网格下的二阶精度Godunov型的PLM格式来求解Elder方程，对一平面激波与不同涡强Rankine涡相互作用下瞬态激波的运动、发展进行了研究。漩涡与激波间相对强度的大小对激波结构的影响明显，弱相互作用诱导激波变形，强相互作用诱导激波变形并产生分叉。计算结果表明，应用非结构化适应网格的PLM格式所得到的数值解较好地反映了瞬态激波结构的有关特征和信息。     

瞬态时域数据合成冲击响应谱算法研究

某液体火箭发动机的部件采用振动台进行模拟冲击环境试验,冲击控制谱的冲击时域波形由软件采用基本波形合成,基本波形有正弦波、合成小波、Chirp波形,而国内常用正弦波合成冲击谱进行冲击环境试验。给出了瞬态冲击数据合成法的算法过程,提取某液体火箭发动机试车过程中的冲击时域数据来合成冲击控制谱的冲击时域波形,计算结果表明算法有效,所合成的冲击时域数据能够满足冲击响应谱的精度要求。     

采用新型基准流场的高超声速内收缩进气道性能分析

通过改变中心体形状,设计了新型轴对称基准流场,可显著降低反射激波强度,明显提高压缩效率。基于该基准流场和传统基准流场,分别设计了两个圆形出口内收缩进气道,并对二者的流场及总体性能进行了数值研究。结果表明,新的进气道设计点和接力点肩点附近激波附面层相互作用减弱,流场结构优于传统进气道,压缩效率明显提高,同时进气道起动性能得到改善。     

流体式高超声速可调进气道流动机理及工作特性分析

针对基于二次流控制的定几何高超声速可调进气道设计概念,给出了其具体的流道实现方案,而后通过全流道仿真分析,检验了该可调进气道在马赫数4~6范围内的可实现性,获得了其工作特性,并对弯曲激波后的总压损失特性、二次流的能量获取及消耗机制等流动机理进行了专门分析。结果表明：该流体式可调进气道能够依靠自身高压驱动二次流来实现对口部波系的调节,使进气道在低马赫数下的流量系数相对于常规定几何高超声速进气道提高24%以上,总压恢复提高7%左右,且最大二次流消耗量只占了进气道捕获流量的1.6%左右。另外,虽然弯曲激波的波后总压和马赫数分布表现出了一定的不均匀性,但是其平均总压恢复系数与相同倾角平面激波相比下降不大。二次流循环流动所消耗的机械能由外部外流剪切力做功补充,而二次流注入会使当地边界层的速度型变得瘦弱,形状因子增大。     

超声速进气道喘振的机理研究

应用数值模拟方法对中心锥中心进气混压式进气道的喘振现象进行了研究。在数值计算的基础上,根据进气道出口截面每个网格点的压力、密度、速度等参数计算了进气道喘振过程中流量系数和总压恢复系数随时间的变化情况。同时给出了在喘振过程中激波振荡的振幅、频率、对应的波系图案。并根据进气道头部分离涡的发展情况以及进气道内通道中状态参数的变化情况对喘振产生的机理进行了分析,认为进气道头部分离涡对喘振的产生起关键的作用。     

超燃冲压发动机隔离段内附面层/激波串相互干扰研究

隔离段内激波串的产生和发展以及激波/附面层相互干扰现象是极为复杂的,有效地进行激波串的组织是研究隔离段的关键所在,而其性能的好坏直接影响着超燃冲压发动机的性能。采用数值模拟的方法对不同来流附面层厚度工况的二维轴对称隔离段内流场流动特性进行了数值计算,分析了附面层/激波相互作用机理和附面层对隔离段激波串及隔离段性能的影响。结构表明:压缩-膨胀-再压缩-再膨胀……的气流流动挤压过程导致激波串的形成,逆压梯度的存在构成了附面层分离;附面层厚度的增加影响着激波串起始位置和结构;随着附面层厚度的增加,出口总压恢复系数和质量平均马赫数降低,且随着反压增大,变化趋势趋于明显。     

The role of viscosity of solids in microparticle cratering

The importance of viscous effects on the impact cratering process has been investigated. The shock wave front region was characterized by the balance of inertia and viscous forces (Reynolds number 1), and by a continuous distribution of all thermodynamic quantities. The width of the shock wave front region and its flow properties were then related to the impact particle size and velocity, and to the target material properties. Experimental data for aluminum demonstrated that cratering characteristics were changed when the impact particle size was the same order of magnitude as the shock wave front region. An analytical model was developed for cratering dominated by this “viscous” flow. Results from this model indicate a substantial decrease in crater radius and increase in crater surface temperature when compared with inviscid analysis. In addition, a new test method was identified to evaluate the viscosity of solids.     

大载荷谐振板的仿真研究

为使跌落式谐振板装置的特性满足大载荷冲击试验的要求,采用有限元方法对谐振板和大载荷（100 kg）谐振板的固有频率及它们在半正弦冲击信号激励下的响应进行计算,得出相应的冲击响应谱。根据计算结果反复调整谐振板的结构尺寸、激励源,使响应点的时域响应和冲击响应谱符合要求。研究结果显示:大载荷对谐振板装置的冲击响应谱有很大的影响,导致响应时域延长、转折点频率降低、冲击谱幅值降低。     

超音速流在正规反射激波系后的参数优化特性

研究了超音速气流中正规反射波加一正激波结构下的参数优化特性，给出了求解这种优化结构的方法，通过计算得到了优化条件存在的区域和优化解的特性，它用可于指导超音速飞行器的进气道及相关装置的设计。     

Risk Factors of Negative Impact on Objects of the Environment upon Accidents during Launches of Rocket-Space Hardware

The probabilistic aspects of rocket accidents during their launching and the motion in the troposphere are discussed. Schemes of forming the probability damage fields of risk recipients (the environment objects) are given. As an example of a use of the developments obtained, probability fields of objects" damage from the impact of an air shock wave are calculated.     

火箭推力室喷管内激波对RBCC性能影响分析

针对火箭基组合循环（RBCC）动力系统引射火箭喷管的工作状况,采用准一维方法,假设引射模态火箭推力室喷管内在某些条件下产生的激波为正激波,分析了正激波的存在条件及其对RBCC动力系统性能的影响.结果表明：引射火箭推力室室压越低或飞行器飞行马赫数越高,引射火箭喷管内越易产生正激波;火箭喷管正激波的产生对RBCC动力系统引射性能及比冲特性有一定影响.     

斜切反喷管性能分析

固体火箭发动机前端斜切反喷管，其结构简单、作用时间短、气动型面具有尖点，并在超音速区有台阶，喷管内存在一系列激波，并伴有流动分离现象。本文从雷诺平均的非定常Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程出发，结合采用Ｂｏｌｄｗｉｎ－Ｌｏｍａｘ代数湍流模型，利用时间相关法及ＭａｃＯｃｏｒｍａｒｋ两步显格式求解，模拟了斜切反喷管流场。计算得到的壁面压强分布与风洞吹风实验测得的压强分布相一致。该方法可应用于斜切反喷管的     

冲压发动机燃烧引起激波运动过程一维分析

分析了冲压发动机喷油燃烧引起内流道内正激波运动的机理,采用一维激波捕捉方法,建立了燃油喷入对正激波运动位置影响的一维仿真模型。通过仿真发现:喷入燃油并逐步增大燃油-空气当量比时,正激波逐步向上游运动;燃油-空气当量比越大,正激波越接近进气道喉道;当燃油-空气当量比增大到一定程度时,正激波距离进气道喉道最近,但并未越过喉道;进一步增大燃油-空气当量比,正激波开始向下游回退进一步分析发现:冲压发动机流道及燃烧组织匹配设计直接影响到正激波在流道内的运动位置,需要在设计中格外重视。燃油-空气当量比与激波位置的关系分析可为冲压发动机设计提供一定的理论参考。     

激波干扰对发汗冷却影响的数值模拟研究

基于宏观表征体元(REV)的数值模拟方法开展了激波干扰对异质发汗冷却影响的数值模拟研究,获得了外部激波干扰与引射气体边界层耦合相互作用流场特征.研究结果表明,不同冷却介质对于冷却效率有显著的影响,冷却介质比热容越大,相同注入率条件下的冷却效果更好;入射激波干扰会显著影响多孔材料表面的压力分布,使得多孔材料内部冷却介质会...     

某固体火箭发动机点火启动过程三维流场一体化仿真

以某固体发动机的燃烧室和喷管为一体化研究对象,采用三维流场控制方程,应用有限体积法计算了发动机点火启动过程中燃烧室和喷管内燃气的流场特性。发动机药柱上的着火点最初出现在药柱星角尖上,然后向四周扩展;在药柱点火初期,燃气压力波先于火焰峰到达喷管;随着燃烧室内燃气压力升高,压力沿轴向分布逐渐平缓;当喷管进口压力与出口背压比达到某一值时,喷管扩张段内出现一道激波,随着压力比的升高,激波最终移出喷管,燃气流速在喷管出口处达到最大值。