THE INTERACTION OF A SHOCK WAVE WITH THE BOUNDARY LAYER IN A REFLECTED SHOCK TUNNEL

The influence of a nontotal reflection on the interaction of a reflected shock wave with the boundary layer in a reflected shock tunnel has been investigated. The calculating method of the velocity, the temperature and the Mach number profiles in the boundary layer in reflected shock fixed coordinates has been obtained. To account for equilibrium real gas effects of nitrogen, the numerical results show that the minimum Mach number in the boundary layer has been moved from the wall into the boundary layer with the increasing of the incident shock Mach number. The minimum Mach number, the shock angle in the bifurcated foot and the jet velocity along the wall to the end plate are reduced owing to the Increasing of the area of nozzle throat. The numerical results are in good agreement with measurements.

TWO DIMENSIONAL SUPERSONIC SHOCK TUNNEL AND ITS APPLICATION

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Experimental investigation of hypersonic flight-duplicated shock tunnel characteristics

Hypersonic air-breathing propulsion is one of the key techniques for future aviation and the ground aerodynamic testing for full scale test models with sufficient test time at flight conditions is of fundamental importance for verifying hypersonic air-breathing engines.Based on the backward detonation-driven concept,the hypersonic flight-duplicated shock tunnel(or JF-12 shock tunnel)has been successfully constructed and calibrated.This facility is capable of reproducing airflow for Mach numbers ranging from 5 to 9 at an altitude of 25-50 km,with a test duration of more than 100 ms.To quantify the performance of the shock tunnel,experiments were conducted to investigate the aerodynamic characteristics of the test flows and the effects of several critical techniques that play important roles in the operation of the shock tunnel.The stagnation pressure was constant within士5%and the average stagnation pressure varied by less than 0.048%/ms.The variation of the stagnation pressure in repeated experiments is less than 2.0%,indicating the good repeatability of the wind tunnel.The non-uniformity of the Mach number in the core flow field at the nozzle exit was within士2.5%.Additional,a uniform flow field is established upstream of the nozzle exit.The axial gradients of the flow field are small since the Mach number varies less than 1.7%/m.Findings regarding the ignition technology,diaphragm ruptures,detonation driver capacity,incident shock-wave decay,and tunnel operation mode are also presented.The findings of this study are not only helpful for operating the shock tunnel,but can also assist the future development of hypersonic wind tunnels.

Aerodynamic force and moment measurement of 10°half-angle cone in JF12 shock tunnel

An aerodynamic force and moment measurement was conducted in JF12 long-testduration detonation-driven shock tunnel of Institute of Mechanics,Chinese Academy of Sciences.The test duration of JF12 is 100–130 ms.The nominal Mach number is 7.0 and the exit diameter of the contoured nozzle is 2.5 m.The total enthalpy is 2.5 MJ/kg which duplicates the hypersonic flight conditions of Mach number 7.0 at 35 km altitude.The test model is the standard aerodynamic force model of 10° half-angle sharp cone.The length of the test model is 1500 mm and the weight is 57 kg.The aerodynamic forces were measured with a six-component strain balance.The angles of attack were set to be à5°,0°,5°,10° and 14°,respectively.The experimental results show that in the 100–130 ms test duration,the signals of strain balance have 3–4 complete vibration cycles.So,the aerodynamic forces and moments can be obtained directly by averaging the signals of balance without acceleration compensation.The force measurement error of repeatability of JF12 is less than 2%.The aerodynamic force coefficients of JF12 are in good agreement with those of conventional hypersonic wind tunnels.For this test model at Mach number 7.0 and total enthalpy of 2.5 MJ/kg,the real-gas effects on aerodynamic force characteristics are not very evident.

Investigation of dual ignition for a detonation-driven shock tunnel in forward driving mode

A detonation-driven shock tunnel is useful as a ground test facility for hypersonic flow research.The forward detonation driving mode is usually used to achieve high-enthalpy flows due to its strong driving capability.Unfortunately,the strong detonation wave front results in diaphragm fragments that disturb the test flow and scratch the nozzle or test models.In this study,a dual ignition system was developed to burst a metal diaphragm without fragmentation in the forward driving mode.A series of experiments were conducted to validate the proposed technique.The influences of the delay time setting on the test conditions were investigated in detail.Numerical simulations were also conducted to obtain a better understanding of the wave processes in the shock tube.The results showed that the dual ignition system solved the diaphragm issues in the forward driving mode.The test time was shortened due to the additional ignition close to the primary diaphragm;the smaller the delay time,the shorter the effective test time.However,a small amount of time loss is considered worthwhile because the severe diaphragm problems have been solved.

Influence of shock attenuation on tailored operation in free piston shock tunnels

The free piston shock tunnel is a type of shock tunnel with high performance. For this type of tunnel, the influence mechanism of shock wave attenuation on tailored operation is explored by numerical simulation and theoretical analysis. By introducing the normalized velocity, the simple constraint equation for shock wave under the tailored operation is deduced. Moreover, the real gas effect is also taken into account in this equation. Based on the equation, the tailored operation of shock tunnels can be predicted with very few calculations. The present study shows that the change rate of the thermodynamic state of the gas behind the shock wave is inconsistent with the attenuation rate of the shock wave, which is the fundamental reason why the wind tunnel achieves tailored operation at a lower Mach number of shock waves. This lower Mach number of shock waves differs from the corresponding ideal value by a factor, which is about the square root of shock attenuation rate.

马赫数10条件下冲压发动机内氢气燃烧特性试验

针对高马赫数超燃冲压发动机面临的高效燃烧组织挑战,本文提出了一种凹腔后缘激波强化的高马赫数超声速燃烧组织技术,并设计了一套燃烧室采用双侧对称布置凹腔结构的三维发动机试验模型。采用OH*基化学发光光谱诊断与壁面测压相结合的试验手段,在自由活塞驱动激波风洞的名义Ma=10流场中,对凹腔上游横向氢气射流的燃烧特性进行了研究,并讨论了模拟流场的重复性,给出了氢气燃烧演化特征、火焰稳定结构及释热特性。不同车次的总压等流场参数表明试验流场具有较高的重复性,可保障氢气燃烧特性的可复现性。通过观察试验过程中OH*基动态发光特征发现,在高焓激波风洞发动机试验中采用燃料提前喷注的方法使发动机流道在空气主流到来之前充盈大量的氢气,进而在主流到达发动机内的瞬间形成所谓“激波管流动-燃烧”效应,使来流空气与氢气接触面发生自点火与剧烈燃烧,产生显著不同于发动机正常工作情况下的点火与燃烧机制,但随着主流趋于平稳,“激波管流动-燃烧”效应消失,在高总温气流的自点火效应与凹腔后缘的X型激波耦合作用下,火焰稳定在凹腔上游近壁面区的氢气射流尾迹区和凹腔后缘附近的全流场中。通过分析壁面压力分布特征发现,凹腔后缘的X型激波实现了燃烧的强化与火焰的稳定,并获得了最显著的释热压升。这些结果表明高马赫数冲压发动机可利用凹腔后缘X型激波强化燃烧和稳定火焰。

The Feature of Weak Shock Wave Propagated in a Overlong Tunnel

Many experiment researches have been developed before. But most of them were carried out with the condition that the tunnel’s ratio of length and diameter (x/D) is under 1000. Recently, the process that compression wave convents into shock wave in the overlong tunnel has also been paid attention. In this paper, features of shock wave as it propagates through a overlong tunnel is investigated, rupturing thin films at the entrance to obtain three kinds of shock wave with different intensities. Then study their features respectively during they propagates through a overlong tunnel with x/D over 6000 at most. Comprehend shock wave more deeply by comparing the results of experiments.

海拔高度对长直坑道内爆炸冲击波传播的影响

为有效表征不同海拔坑道内爆炸冲击波的传播特征,利用非线性显式动力学有限元软件AUTODYN,研究了海拔高度对长直坑道内爆炸冲击波传播的影响规律,探讨了高海拔环境对坑道内冲击波传播的影响,基于量纲分析,建立了适用于不同海拔高度典型坑道内冲击波峰值超压的计算模型,并通过数值计算进行了验证。结果表明:随着海拔高度升高,坑道内爆炸冲击波波阵面传播速度与径向的冲击波参数偏差增大,平面波形成距离增加,冲击波峰值超压降低;在0~4000 m范围内,海拔高度每升高1000 m,冲击波冲量降低约0.91%。结合Sachs无量纲修正方法和量纲分析,推导出不同海拔高度冲击波峰值超压的理论分析模型,模型计算结果与数值计算结果的相对偏差不大于10%,能够为高海拔环境下坑道内爆炸冲击波的传播提供理论依据。

风洞来流参数影响的气动热数据不确定度评估

激波风洞是开展气动热预测的重要手段,气动热数据的准确预示对降低高超声速飞行器热防护系统设计裕度、增加飞行器有效载荷和射程有重要意义,因此对激波风洞气动热试验数据开展不确定度研究很有必要。对激波风洞重复性运行导致的热流不确定度进行研究,首先采用蒙特卡洛方法,对重复运行58车次的激波风洞测量数据进行分析,获得了风洞来流参数随机分布不确定性。结果表明来流速度的相对不确定度较小,为1.02%;而来流压力的相对不确定度较大,为3.54%。然后选取来流温度、来流密度、来流速度、壁面温度4个不确定性输入变量,采用拉丁超立方抽样法生成样本,通过气动热数值计算获得钝锥模型壁面热流数据,采用非嵌入式多项式混沌方法进行不确定度量化和敏感性分析。结果表明在钝锥头部和锥体大部分区域,风洞重复性运行导致的热流不确定度约为4%~5%;敏感性分析结果显示壁面热流对来流速度最敏感。因此如果需要降低热流数据不确定度,就需要降低风洞来流速度不确定度,这需要通过将激波管激波马赫数控制在更小的偏差范围内来实现。

隧道内障碍物对爆破冲击波传播特性影响研究

隧道掌子面开挖爆破产生的冲击波对施工安全构成极大威胁,为研究隧道内障碍物对掌子面开挖爆破产生的冲击波传播特性影响,依托宁攀高速公路胜利隧道,采用动力分析软件ANSYS/LS-DYNA模拟爆破冲击波在隧道内障碍物段的传播,并采用现场测试方法对数值模拟结果进行验证。研究表明:正常衰减的冲击波传播至障碍物面上方2 m处超压迅速增长4.1%,通过障碍物后由于绕流作用超压增长2.2%,障碍物上方冲击波总体呈现增强-衰减-再增强-再减小的特性;障碍物中心轴线前5 m处反射冲击波超压开始高于初始冲击波,反射冲击波传播至障碍物面时超压峰值增长至初始冲击波的2.4倍;障碍物对正后方0.5 m范围内超压峰值有一定的降低作用,0.5~2 m范围内冲击波超压有所增长,随后恢复为正常超压衰减。现场测试结果表明,障碍物前2.5 m处形成2个超压峰值,经障碍物表面反射第2个冲击波超压峰值为初始峰值的2.95倍。

大尺寸自由活塞激波风洞自由流参数诊断方法

高焓激波风洞自由流具有一定程度的热化学非平衡,使得流场参数的确定存在困难。针对大尺寸自由活塞高焓激波风洞的总温2 700~4 700 K、总压5.6~20.3 MPa条件,采用非接触吸收光谱技术、接触测量技术等测试技术,结合多温度多组分数值模拟方法,共同诊断喷管名义马赫数10出口自由流的参数。结果显示,温度测量值与计算值最大偏差小于7.5%,速度测量值与计算值最大偏差小于5%,NO浓度测量值与计算中最大偏差小于12%。

基于立方型气体状态方程的激波风洞准一维流动数值研究

采用基于立方型气体状态方程的准一维流动数值模拟方法研究了反射式高焓激波风洞的真实气体流动,重点关注了高压真实气体效应对风洞全场流动时空结构和驻室区气流参数的影响,并以理论分析揭示了高压真实气体效应对激波管内流动的作用机理。研究表明:对于以冷高压气体驱动的激波风洞,使用考虑分子体积和分子间作用力的真实气体状态方程能够更准确地描述气体的状态和风洞内的流动状况。高压真实气体效应主要在冷驱动气体中发生作用,其作用效果主要是使当地声速增大,从而使得入射稀疏波和反射稀疏波的传播速度加快;另一方面,高压气体效应在高温气体效应较显著的被驱动气体中作用微弱,且对激波管产生激波的强度和激波后的流动状态影响甚微。稀疏波的加快传播改变了激波管波系的相干时空关系。提前抵达的稀疏波可在一定情况下侵蚀激波风洞的有效试验时间。对于所测试的激波风洞构型,在150 MPa氢气驱动110 kPa氮气的工况下,高压效应导致的有效试验时间缩短约38%。适当加长驱动段长度和采用高温气体驱动均可有效减弱高压真实气体效应的影响。

真实气体效应和热化学反应对激波风洞流场特征参数的影响研究

真实气体效应会改变气体热物性,热化学反应则会影响激波波后状态,两者将共同影响激波风洞流场特征参数。利用真实气体状态方程和热化学平衡假设,建立了一套真实气体热物性和波后参数快速计算方法,研究了真实气体热物性参数的变化及热化学反应对波后参数的影响。通过考虑真实气体和热化学非平衡效应的准一维计算方法,结合气动理论分析,研究了真实气体效应和热化学反应对风洞流场时空结构和驻室参数的影响。结果表明,真实气体的声速、焓以及熵等参数与理想气体存在显著差异,且偏差随着压强的增加而增大。热化学反应使得激波波后气体温度和压强分别低于和高于定比热比假设的结果,且波后状态接近热化学平衡。真实气体效应则使得膨胀波波头传播速度增加及入射激波马赫数减小,影响风洞流场的时空结构,并可能导致有效实验时间减小。

基于动态补偿的半导体应变天平短时测力技术研究

脉冲风洞是模拟高马赫数的重要地面设备,有效试验时间为毫秒量级,天平采集到的信号为气动力信号和振动产生的惯性力的合力,因此提高测量精度的途径之一为提高模型-天平-支杆组成的脉冲风洞测力系统(MBS系统)的固有频率,降低惯性力的占比。固有频率的提高必然导致天平灵敏度下降,对于高马赫数或小攻角的小载荷测量,过小的输出信号可能会淹没在噪音中。针对以上难题,将半导体应变计应用于天平设计中,达到提高天平刚度同时提高输出灵敏度,并应用动态补偿技术,缩短天平响应时间,降低试验不确定度。新天平静态校准表明,法向力校准结果优于3‰,俯仰力矩校准结果优于1‰,各分量输出提高约40倍;针对试验模型进行动态校准,设计动态补偿滤波器,加速试验输出信号收敛,提高数据品质。动态补偿后的测试系统响应时间可缩短至3 ms,可以满足有效试验时间为10 ms量级的脉冲风洞气动数据测量需求。

OXYHYDROGEN COMBUSTION AND DETONATION DRIVEN SHOCK TUBE

The performance of combustion driver ignited by multi-spark plugs distributed along axial direction has been analysed and tested. An improved ignition method with three circumferential equidistributed ignitors at main diaphragm has been presented, by which the produced incident shock waves have higher repeatability, and better steadiness in the pressure, temperature and velocity fields of flow behind the incidence shock, and thus meets the requirements of aerodynamic experiment. The attachment of a damping section at the end of the driver can eliminate the high reflection pressure produced by detonation wave, and the backward detonation driver can be employed to generate high enthalpy and high density test flow. The incident shock wave produced by this method is well repeated and with weak attenuation. The reflection wave caused by the contracted section at the main diaphragm will weaken the unfavorable effect of rarefaction wave behind the detonation wave, which indicates that the forward detonation driver can be applied in the practice. For incident shock wave of identical strength, the initial pressure of the forward detonation driver is about 1 order of magnitude lower than that of backward detonation.

爆破冲击波在隧道变截面断面的传播特性

为研究爆破冲击波在隧道内复杂环境下的传播规律,以老营盘隧道为依托,通过建立三维数值模型,在LS-DYNA软件中分析了隧道断面变化不同系数下冲击波的传播规律。研究结果表明:冲击波经过变截面后,总体上以平面波的形式向前传播;冲击波传播至隧道断面扩大界面时,冲击波超压衰减速度加快,超压峰值降低;当断面扩大1.5倍时,冲击波冲量衰减系数为1.158,冲击波能量残留比率为74.5%;断面扩大倍数越大,冲击波超压衰减速度越大,能量衰减幅度越大;冲击波传播至隧道断面缩小界面时,冲击波超压增大,其衰减速度减缓,导致冲击波造成的损伤程度增加;当断面缩小系数取0.5时,冲击波冲量增强系数为0.687,冲击波能量放大系数为2.122;断面缩小系数越小,冲击波造成的损伤越大。

H型巷道内采用不同布置方式的双爆源瓦斯爆炸传播特性

为探究复杂巷道内多爆源瓦斯爆炸传播特性及热冲击动力学机制,运用计算流体力学软件Fluent,以H型巷道为模型,在巷道内设置同侧、相对、对角3种双爆源布置方式。研究发现:巷道内的2处爆源同时起爆后,前驱冲击波沿巷道未燃区传播,当两股冲击波相遇时,压力叠加,冲量抵消,在压力叠加区火焰传播受阻,导致火焰传播速度放缓甚至反向;相较于单爆源爆炸,双爆源工况中导致巷道内特定区域如联络巷、岔口中心及其边壁的压力更高;同侧和对角布置工况下的压力极值区出现在巷道封闭端,相对布置工况下的压力极值区出现在分岔口中心处。

扰流板参数对坑道爆炸冲击波衰减效率的影响

为研究扰流板对坑道内爆炸冲击波的超压传播影响规律,对坑道内爆炸冲击波传播过程进行了理论分析和数值模拟。模拟涵盖了扰流板不同数量、间距、尺寸、迎波角、以及布置方式参数,通过对比超压理论计算结果和仿真结果,验证了计算方法的可行性。坑道内扰流板数量对冲击波衰减的影响最大,可将爆炸冲击波的衰减效率提升35.8%;扰流板间距对爆炸冲击波衰减效率的提升仅次于扰流板数量,在进行扰流板布置时,优先考虑数量和间距的配合;在进行扰流板冲击波试验时,尽可能减小前方扰流板尺寸,加大后方扰流板尺寸,减轻爆炸冲击波对扰流板自身的毁伤,延长爆炸冲击波超压峰值到来的时间;迎波角为70°时,相对布设优于交错布设;迎波角为75°时,交错布设优于相对布设。

克泥效工法对盾构隧道地表变形的作用规律研究

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