非平衡化学反应流场NS方程计算研究

介绍一种新的与化学问题相耦合的NS方程数值方法,用来计算有限速率化学反应再入流场.采用迎风TVD差分格式的激波捕捉法,求解控制方程。本项研究针对轴对称流动。然而,可以直接推广到三维流动和其它的化学反应系统。所采用的整个泰氟隆-空气化学反应模型是由23个化学组元和35个化学反应所组成。对钝头球锥体全流场(包括前体和近尾迹)进行了数值模拟,获得了充分收敛的数值解。对清洁空气流场计算的峰值电子数密度与实验结果符合很好。     

Numerical analysis of supersonic gas-dynamic characteristic in laser cutting

The influence of the processing parameters on the dynamic characteristic of supersonic impinging jet in laser cutting is studied numerically. The numerical modeling of a supersonic jet impinging on a plate with a hole is presented to analyze the gas jet–workpiece interaction. The model is able to make quantitative predictions of the effect of the standoff distance and exit Mach number on the mass flow rate and the axial thrust. The numerical results show that the suitable cutting range is slightly different for different exit Mach number, but the optimal cutting parameter for certain exit total pressure is nearly changeless. So the better cut quality and capacity can be obtained mainly by setting the suitable standoff distance for a certain nozzle pressure.     

高超声速化学非平衡流动MHD效应的数值模拟

对偶极子磁场作用下的三维钝头体高超声速黏性绕流的化学非平衡流动进行了数值模拟.计算结果表明,在偶极子磁场强度为1.353 T时,与无磁场作用时相比,激波的脱体距离增加,增幅约为50%;壁面压力系数下降,局部下降最大达37%;壁面摩擦系数减小,局部最大可减小20%.同时,计算结果与磁场作用下的冻结流进行了比较,结果显示化学非平衡流中激波脱体距离比冻结流中小50%,滞止点温度低一半.     

The connection between sound production and jet structure of the supersonic impinging jet

An experimental investigation into the sound-producing characteristics of moderately and highly underexpanded supersonic impinging jets exhausting from a round convergent nozzle is presented. The production of large plate tones by impingement on a square plate with a side dimension equal to 12 nozzle exit diameters is studied using random and phase-locked shadowgraph photography. Discrete frequency sound is produced in the near-wall region of the jet when a Mach disk occurs upstream of the standoff shock wave. Tones cease when the plate distance is approximately 2.2 free-jet cell lengths and the first and second shock waves are located in the free-jet positions. The production of impulsive sound appears to be associated with the collapse of the standoff shock wave during a portion of the oscillation cycle. Results from unsteady plate-pressure measurements indicate that plane-wave motion occurs in the impingement region and a secondary pressure maximum is observed on the plate adjacent to the flow region where sound appears to originate.     

高超声速圆锥边界层转捩实验研究

在高超声速静音风洞内, 通过基于纳米粒子示踪的平面激光散射(nano-tracer-based planar laser scattering, NPLS)技术、高频压力传感器和温敏漆(temperature sensitive paints, TSP)技术开展了0°攻角条件下7°直圆锥高超声速边界层转捩相关实验研究, 得到了圆锥边界层由层流发展至湍流完整过程的NPLS图像, 清晰地展示了第2模态波的"绳状"结构, 尖锥与钝锥边界层的NPLS结果表明尖锥边界层转捩中第2模态波占主导, 而钝锥边界层在转捩前出现波长约为第2模态波波长5倍(甚至更长)、特征频率不高于31 kHz的狭长涡结构; 采用功率谱密度(power spectrum density, PSD)分析、互相关和N值计算对高频脉动压力数据进行分析, 得到了边界层内扰动波的发展规律, 在尖锥和钝锥中均观察到了沿流向第2模态波幅值先增大后减小、特征频率逐渐降低, 低频成分逐渐增加, 表明边界层发展过程中第2模态率先发展达到饱和, 而后逐渐衰减, 而低频模态则逐渐发展; 通过TSP技术得到了不同单位Reynolds数下的圆锥表面温升分布, 结果表明, 随单位Reynolds数增大, 边界层转捩阵面前移.      

Visualization of shock waves around hypersonic spiked blunt cones using electric discharge

The hypersonic flow fields around a 120⁰ apex angle blunt cone fitted with spikes have been visualized using electric discharge technique at Mach 5.75 in a hypersonic shock tunnel. The blunt cone has been fitted with a flat tipped spike and a flat aerodisc tipped spike assembly. The length of the aerodisc tipped spike assembly has been kept equal to the model base diameter (L/D=1) and the length of the flat tipped spike has been kept at 12mm. The flow field pictures reveal all the salient features of the flow fields around the spiked bodies. Numerical simulations carried out to complement the experiments agree well with the experimental pictures.     

DNS of compressible turbulent boundary layer around a sharp cone

Direct numerical simulation of the turbulent boundary layer over a sharp cone with 20° cone angle (or 10° half-cone angle) is performed by using the mixed seventh-order up-wind biased finite difference scheme and sixth-order central difference scheme. The free stream Mach number is 0.7 and free stream unit Reynolds number is 250000/inch. The characteristics of transition and turbulence of the sharp cone boundary layer are compared with those of the flat plate boundary layer. Statistics of fully developed turbulent flow agree well with the experimental and theoretical data for the turbulent flat-plate boundary layer flow. The near wall streak-like structure is shown and the average space between streaks (normalized by the local wall unit) keeps approximately invariable at different streamwise locations. The turbulent energy equation in the cylindrical coordinate is given and turbulent energy budget is studied. The computed results show that the effect of circumferential curvature on turbulence characteristics is not obvious.     

Visualization of unsteady shock oscillations in the High-enthalpy flow field around double cones

The presence of an adverse pressure gradient, shock/shock interaction and shock wave/boundary layer interaction often induces flow separation around bodies. However, the effect of dissociated flow on separated flow characteristics, especially at hypersonic speeds, is still not clear, and considerable differences are observed between experiments and numerical simulations. In this investigation, the unsteady separated flow features around double cones are visualized in the Shock Wave Research Center (SWRC) free-piston driven shock tunnel at a nominal Mach Number of 6.99 using multiple optical techniques. The time resolved shock structure oscillations in the flow field around double cones (first cone, semi-apex angle = 25°; second cone, semi-apex angles=50°, 65°, 68° and 70°) have been visualized using a high-speed image converter camera (IMACON) at a nominal stagnation enthalpy of 4.8 MJ/kg. In addition, flow visualization studies around the double cone is also carried out using Schlieren and double exposure holographic interferometry in order to precisely locate the separation point and measure the separation length. The presence of a triple shock structure in front of the second cone and a non-linear unsteady shock structure oscillation in the flow field are the significant results from visualization studies on the 25° /65°, 25° /68° and 25°/70° double cones. On the other hand, the flow field around 25° /50° is relatively steady and Type V shock/shock interaction is observed. Illustrative numerical simulation studies are carried out by solving N-S equations to complement the experiments. The simulated flow features around a double cone agree well qualitatively with experiments.     

On the Global Existence and Stability of a Multi-Dimensional Supersonic Conic Shock Wave

We establish the global existence and stability of a three-dimensional supersonic conic shock wave for a compactly perturbed steady supersonic flow past an infinitely long circular cone with a sharp angle. The flow is described by a 3-D steady potential equation, which is multi-dimensional, quasilinear, and hyperbolic with respect to the supersonic direction. Making use of the geometric properties of the pointed shock surface together with the Rankine–Hugoniot conditions on the conic shock surface and the boundary condition on the surface of the cone, we obtain a global uniform weighted energy estimate for the nonlinear problem by finding an appropriate multiplier and establishing a new Hardy-type inequality on the shock surface. Based on this, we prove that a multi-dimensional conic shock attached to the vertex of the cone exists globally when the Mach number of the incoming supersonic flow is sufficiently large. Moreover, the asymptotic behavior of the 3-D supersonic conic shock solution, which is shown to approach the corresponding background shock solution in the downstream domain for the uniform supersonic constant flow past the sharp cone, is also explicitly given.     

马赫反射的一种简便的数值模拟方法——分裂拟特征线法

本文提出马赫反射的一种简易、有效的数值模拟方法——分裂拟特征线法,并对平面激波碰到斜劈时所形成的马赫反射进行了模拟计算。具体格式设计灵活,程序实现容易,运算量和信息量比已有的其它方法都有很大的节省。计算结果表明,马赫反射图象和流场基本特征与已有的实验或计算结果比较,是比较吻合的。     

Influence of blunt-cone tip temperature on the laminar-turbulent transition in hypersonic boundary layers

In the present paper, we report on the results of a combined experimetal and numerical study of the laminar-turbulent transition at Mach number 5.95 in the boundary layers of 7-deg cones with a small nose-tip bluntness radius (down to 1.5 mm). The tip temperature of the model was varied in the range from 90 to 440 K. It was confirmed that the small nose-tip bluntness substantially shifts the position of the transition in downstream direction. This effect was also retained in testing the models with local heating/cooling of the cone tip. It is shown that for the experimental conditions implemented in the Transit-M wind tunnel, ITAM SB RAS, the local heating of blunt cone tips exerts almost no influence on the position of the transition. The local cooling of the cone tip with R = 1.5 mm leads to a shift of the transition position in upstream direction.     

高能闪光照相中钨球散射规律研究

 用解析法和Monte Carlo法研究了钨球闪光X光照相的散射照射量空间分布随钨球半径、系统中元件构成以及保护器件与记录平面间距的变化规律。指出散射照射量的空间分布是不均匀的，它随球半径增加而变大；保护器件是散射照射量的主要来源，增加从保护器件到记录平面的距离，可以降低散射分布不均匀性，以及有效地减少散射。     

Investigation of interaction between methanol fed tandem porous spheres burning in a mixed convective environment

Flame interaction during the burning of two porous spheres in tandem arrangement fed with methanol and subjected to a mixed convective environment, has been studied experimentally and numerically. Porous sphere technique is employed for experimentally simulating the burning characteristics of methanol transpired spheres of different sizes, separated by fixed distances. The mass burning rates from both the spheres and visible flame stand-off distances from the sphere surfaces have been measured in the experiments. In the numerical simulations, transient, axisymmetric, mass, momentum, species and energy conservation equations are solved using a finite volume technique based on non-orthogonal semi-collocated grids. Features of the numerical model include finite rate chemistry and temperature and mixture composition dependent thermo-physical properties. Burning of tandem porous spheres in an air stream flowing vertically upwards, at atmospheric pressure has been simulated for different sphere sizes, separation distances and free stream velocities. The numerical predictions have been compared with experimental results. Results reveal that when two spheres burn one over the other, the transition from envelope to wake flame is delayed when compared with that of an isolated sphere. For two spheres of same diameter burning one over the other, depending on the separation distance, flame blows-off after the occurrence of transition from envelope to wake flame in the bottom sphere. For the case of larger sphere at the top, either the flame stabilises in the recirculation zone formed in between the spheres or the flame from the smaller sphere lifts off and stabilises near the front portion of the larger sphere, depending on the separation distance. At higher separation distances, around four times the diameter of the sphere, both the spheres burn independently. The burning rate undergoes complex variations with air stream velocity depending on the sphere sizes and separation distances.     

进入轨道偏差对火星科学实验室气动力特性的影响

针对火星科学实验室(MSL)高超声速进入过程,利用三维并行程序求解流体力学Navier-Stokes方程,耦合真实气体模型,分析火星大气中真实气体效应对进入器气动力特性的影响量在进入轨道发生偏差时的变化规律.结果表明:对海盗号的计算结果与飞行数据符合很好,验证了火星大气真实气体模型和计算方法;真实气体效应影响下,激波层厚度大为减小,温度下降明显,进入器阻力系数明显增加,升力系数变化不大,俯仰力矩系数增加,基准状态下配平攻角较完全气体减小约2.2°;高度不变,Ma数增加导致阻力系数和俯仰力矩系数增大,配平攻角和完全气体的差值由1.6°增加到2.6°,表明Ma数变大时真实气体效应引起的气动力变化增强;Ma数不变,高度增加略微减弱波后化学反应,对进入器气动力特性基本没有影响.     

平面激波经下降台阶后的马赫效应

As a plane shock wave with shock mach number Mi propagates down a backward step of height H (fig 1) a part of the shock front turns to be curvilinear It reflects from the horizontal part behind step.This unsteady regular reflection eventually becomes Mach reflection.We present here the results of shock tube experiment (M_i ≤ 2.20) and numerical simulation of this phenomena, say the transition from regular reflection (RR) to Mach reflection (MR).The dependence of the position of transition L_k and critical angle of transition ω_Ck on strength of the impinging plane shock M_i and height of step H are analysed.Our experimental and numerical results are compared with the theoretical criLerion of transition of Iton & Itaya^[15].It should be mentioned that the numerical method of FLIC type with triangular mesh developed in^[13] is successful.     

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.     

辐射传热对微重力环境下预混火焰传播特性的影响

1引言在火焰中，辐射过程是一种重要的传热方式。对该过程尽可能精确的计算，对于改进燃烧设备的设计、改善设备的运行性能十分有益。在正常重力环境下，与其它的释热现象相比，预混火焰中的辐射热损失十分微弱，因而，过去对预混火焰的分析中，往往忽略了辐射热损失的影响。近年来，对微重力（ug）环境下的预混火焰的研究结果表明，可燃极限与＃s最小点火能无关，自媳灭火焰（SEFs）发生时；其释放的能量比通常观察到的点火极限时的能量大几个数量级山，因此火焰伸张并不能解释“g环境下观察到的实验结果，辐射热损失可能是影响＃g火焰可…     

基于Ludwieg管的高超声速边界层转捩实验

高超声速边界层层/湍流转捩是高超声速飞行器气动力和气动热设计中的难点和热点问题.为了降低开展高超声速边界层不稳定性与转捩实验研究的门槛,研究基于Ludwieg管原理设计并建造了一座Mach 6高超声速管风洞,重点对Ludwieg管风洞的启动和运行过程开展了数值模拟,分析了储气段弯管布局对试验段流场的影响;之后,对该高超...     

激光空泡刚性半球面内运动

采用甚高速照相技术与建立激光空泡在刚性半球壁面内的运动模型相结合的方法,确定了激光空泡在刚性半球面壁内的运动特性与无量纲距离的关系,提出了最佳无量纲距离概念。结果表明:半球反射面的半径与激光空泡最大半径之比小于1.1时,激光空泡在第1次膨胀时就会产生严重的变形并弹出半球面,并产生空化泡和空蚀,它们均会严重影响激光声的传播。该比值在1.1~3.3时,激光空泡将在第3次收缩之前接触半球面,容易对壁面造成空蚀。在该比值大于3.3的情况下,激光空泡在第3次收缩之前不会接触半球面,对激光声的传播和反射特性影响较小。如果考虑把空泡第1次溃灭时产生的激光声的声学中心控制在击穿点时,需要把该比值控制在5以上。     

Determination of tip–sample interaction forces from measured dynamic force spectroscopy curves

The forces between a sharp tip and a sample are characteristic for different sample materials. A new method for quantifying the elastic tip–sample interaction forces from measured frequency vs. distance curves is presented. The dynamic force–spectroscopy curves investigated were obtained by dynamic force microscopy under ultrahigh vacuum (UHV) conditions for large vibration amplitudes with commercial levers/tips. The full non-linear force–distance relationship is deduced via a numerical algorithm, where the equation of motion describing the oscillation of the tip is solved explicitly. The elastic force distance dependence can be determined by fitting the results of a computer simulation to experimental frequency vs. distance data. The obtained force–distance curves can be compared quantitatively with theoretical models.