Tubular limiting stream surface: “tornado” in three-dimensional vortical flow

A new physical structure of vortical flow, i.e., tubular limiting stream surface (TLSS), is reported. It is defined as a general mathematical structure for the physical flow field in the neighborhood of a singularity, and has a close relationship with limit cycles. The TLSS is a tornado-like structure, which separates a vortex into two regions, i.e., the inner region near the vortex axis and the outer region further away from the vortex axis. The flow particles in these two regions can approach to (or leave) the TLSS, but never could reach it.     

Instability theory of shock wave in a channel

The instability theory of shock wave was extended from the case with an infinitefront to the case of a channel with a rectangular cross section.First,themathematical formulation of the problem was given which included a system ofdisturbed equations and three kinds of boundary conditions.Then,the general solutionsof the equations upstream and downstream were given and each contained fiveconstants to be determined.Thirdly,under one boundary condition and oneassumption,it was proved that all of the disturbances in front of the shock front andone of the two acoustic disturbances behind the shock front should be zero.Theboundary condition was that all of the disturbed physical quantities should approach tozero at infinity.The assumption was that only the unstable shock wave was concernedhere.So it was reasonable to assumeω=iγ,γwas the instability growth rate andwas a positive real number.Another kind of boundary conditions was that the normaldisturbed velocities should be zero at the solid wall of the cha     

Instability theory of shock wave in a shock tube

The instability theory of shock wave in a shock tube including the effects of tube wall and contact surface is studied. The experimental data of unstable shock wave coincide with one of instability criteria derived in the present paper.     

Solving shock wave with discontinuity by enhanced differential transform method (EDTM)

An enhanced differential transform method (EDTM), which introduces the Padé technique into the standard differential transform method (DTM), is proposed. The enhanced method is applied to the analytic treatment of the shock wave. It accelerates the convergence of the series solution and provides an exact power series solution.     

Interaction of a gasdynamic shock with small disturbances

The stability of shock wave based on the definition of Landau and Lifschitz^[1] is treated in this paper. This is tantamount to solving the problem of interaction of small disturbances with a shock wave. Small disturbances are introduced on both sides of a steady, non-dissipative, plane shock wave. Landau et al.^[1] obtained the stability criterionM ₁>1,M ₂<1 for small disturbances which are travelling in the direction perpendicular to the shock wave. In the present paper, we assume that the small disturbances may be two dimensional, i.e. they may be propagating in the direction inclined to the shock wave. The conclusions obtained are: regardless of whether the incident wave and diverging wave are defined according to the direction of the phase velocity or the group velocity, the shock wave is unstable for some frequencies and longitudinal wave lengths of the disturbances, even if the conditionsM ₁>1,M ₂<1 are fulfilled. Then several experiments are proposed, and the problem of ways to define the incident wave and diverging wave is discussed. The meaning of this problem is illustrated. The same results can be obtained for the steady shock wave in a tube.     

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.     

Oblique shock wave with sweep

An attached planar, oblique shock with sweep is investigated for the inviscid flow of a perfect gas. The ratio of specific heats, freestream Mach number, and wedge angle in the plane of the freestream velocity are prescribed, with the sweep angle as a free parameter. Explicit relations are provided for jump and detachment conditions. A number of trends, some non-intuitive, are discussed, e.g., the downstream Mach number may increase with sweep.     

冷激波灭火系统中激波对灭火效果和周边环境的影响

为了评估冷激波灭火弹爆炸后形成的激波对灭火效果和周边环境的影响,建立了一套纹影实验装置。通过纹影实验,观察了小尺寸下不同灭火介质爆炸抛撒后激波的形成和传播,并推算了冷激波灭火弹爆炸后油盆边缘附近的波后质点速度。观察发现,水基灭火介质爆炸抛撒后没有形成激波;而粉基灭火介质尽管爆炸抛撒后形成激波,但在油盆边缘附近激波强度较弱,波后质点速度小。与介质抛撒引起的可燃气体介质运动相比,激波对加快可燃气体介质运动的影响可以忽略。最后,通过高速摄影实验验证了激波对灭火效果的影响是可以忽略的。因此,冷激波系统中,激波对灭火效果和周边环境的影响是可以忽略的。     

Oblique shock wave with sweep II

This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

冲击波作用下乳化炸药压力减敏的表征方法

引入一个新的物理量压力减敏程度,来更合理地表征乳化炸药发生压力减敏的难易程度,为研究其作用机理提供量化的分析工具。分别利用乳化炸药发生压力减敏前后的爆炸冲击波峰压及其对数、冲击波能量和总能量计算压力减敏程度,比较并分析计算结果的优劣。结果表明,几个参数计算的结果都能达到相近的效果,用冲击波峰压计算起来简单方便,冲击波能量计算效果较好。用冲击波参数计算的压力减敏程度能够反映乳化炸药压力减敏的本质,建议采用冲击波峰压计算压力减敏程度,在数值差别不明显时采用冲击波能量来计算。     

Experimental and numerical studies of underwater shock wave attenuation

The attenuation of an underwater shock wave by a thin porous layer is studied both experimentally and numerically. The shock waves are generated by exploding 10 mg silver azide pellets and the pressures at different distances from the explosion center are measured. Measurements are also carried out with a gauze layer placed between the explosion source and the pressure gauge. The results with and without the gauze layer are compared evaluating the shock wave attenuation. Numerical simulations of the phenomenon are also carried out for a simple wave attenuation model. The results are compared with the experimental data. Despite the simple mathematical model of wave attenuation, the agreement between the experimental and numerical results is reasonable.Received: 22 October 2002, Accepted: 17 June 2003, Published online: 5 August 2003PACS: 47.11.+j, 47.40.Nm, 47.55.Mh     

The formation of a secondary shock wave behind a shock wave diffracting at a convex corner

This paper deals with the formation of a secondary shock wave behind the shock wave diffracting at a two-dimensional convex corner for incident shock Mach numbers ranging from 1.03 to 1.74 in air. Experiments were carried out using a 60 mm 150 mm shock tube equipped with holographic interferometry. The threshold incident shock wave Mach number () at which a secondary shock wave appeared was found to be = 1.32 at an 81° corner and = 1.33 at a 120° corner. These secondary shock waves are formed due to the existence of a locally supersonic flow behind the diffracting shock wave. Behind the diffracting shock wave, the subsonic flow is accelerated and eventually becomes locally supersonic. A simple unsteady flow analysis revealed that for gases with specific heats ratio the threshold shock wave Mach number was = 1.346. When the value of is less than this, the vortex is formed at the corner without any discontinuous waves accompanying above the slip line. The viscosity was found to be less effective on the threshold of the secondary shock wave, although it attenuated the pressure jump at the secondary shock wave. This is well understood by the consideration of the effect of the wall friction in one-dimensional duct flows. In order to interpret the experimental results a numerical simulation using a shock adaptive unstructured grid Eulerian solver was also carried out. Received 1 May 1996 / Accepted 12 September 1996     

激波聚焦诱导点火和爆轰的数值研究

以二维轴对称多组分Euler方程为基础,采用非正交结构化网格和改进的波传播算法,模拟了激波在抛物形反射壁面聚焦反射诱导点火和爆轰的过程,描述了其流场形态。讨论了预混气组成、入射激波强度及反射壁面形状对点火和爆轰的影响。结果表明,激波在抛物形反射壁面顶点处聚焦反射可形成局部高温高压区域,该区域在一定条件下可点燃预混气甚至形成爆轰,其中低稀释剂浓度的预混气、较大的入射激波Mach数和较深的反射壁面有利于可燃预混气形成爆轰。     

液滴对爆炸冲击波的衰减作用

为分析液滴对舰船舱内爆炸冲击波的耗散与衰减作用,通过有限元分析方法,建立冲击波作用于不同尺寸单个液滴和多排液滴的模型,分析冲击波与单个及多个液滴的作用过程及液滴形态变化,对冲击波衰减规律进行分析总结。得到结论如下:单个液滴模型中,小液滴破碎更迅速,破碎的规律性强;大液滴抛撒现象发生较早,抛撒出的小液滴数目多,但整体变化规律性偏差;不同尺寸单个液滴对冲击波有一定的衰减作用,衰减率随液滴尺寸增大而增大,线性规律较明显;成排液滴对冲击波有明显的衰减作用,相同液滴密度下衰减率随着液滴数量的增多而增大,呈现明显的线性特性。     

Application of underwater shock wave and laser-induced liquid jet to neurosurgery

Paper deals with applications of underwater shock waves to medicine. A historical development of underwater shock wave generation by using pulsed Ho:YAG laser beam irradiation in water is briefly described and an overview is given regarding potential applications of shock waves to neuro-surgery. The laser beam irradiation in a liquid-filled catheter produces water vapor bubble and shock waves intermittently produces micro-liquid jets in a controlled fashion from the exit of the catheter. Correlations between shock dynamics and bubble dynamics are emphasized. To optimize the jet motion, results of basic parametric studies are briefly presented. The liquid jet discharged from the catheter exit has an impulse high enough to clearly exhibit effectiveness for various medical purposes. In liquid jets we observed reasonably strong shock waves and hence invented a compact shock generator aiming to apply to microsurgery. We applied it to a rat's bone window and developed an effective method of brain protection against shock loading. The insertion of Gore-Tex® sheet is found to attenuate shock waves drastically even for very short stand off distance and its physical mechanism is clarified. The laser-induced liquid jet (LILJ) is successfully applied to soft tissue dissection. Animal experiments were performed and results of histological observations are presented in details. Results of animal experiments revealed that LILJ can sharply dissect soft tissue with a minimum amount of liquid consumption, while blood vessels larger than 0.2 mm in diameter are preserved. Shock waves and LILJ have a potential to be indispensable tools in neuro-surgery.This paper was based on work that was presented at the 2nd International Symposium on Interdisciplinary Shock Wave Research, Sendai, Japan, March 1–3, 2005.Communicated by K. Takayama PACS 42.62.Be, 47.40.-x, 42.62.-b     

Stability of converging cylindrical shock waves

An experimental and numerical study was made of converging cylindrical shock waves. The goal of the present study was to clarify the movement and instability of the converging cylindrical shock waves. Experiments were conducted in an annular shock tube of 230 mm o.d. and 210 mm i.d. connected to a cylindrical test section of 210 mm diameter. Double exposure holographic interferometry was used to visualize the converging cylindrical shock waves. Incident shock Mach numbers ranged between 1.1 and 2.0 in air. A numerical simulation was conducted using the TVD finite difference scheme. It was found in the experiments that although the initial shock wave configuration looked cylindrical, it was gradually deformed with propagation towards the center and finally showed mode-four instability. This is attributable to the existence of initial disturbances which were introduced by the struts which supported the inner tube of the annular shock tube. This trend was significant for stronger shock waves indicating that at the last stage of shock wave convergence the initial perturbations of the converging cylindrical shock wave were amplified to form the triple point of Mach reflection. The numerical results correctly predicted the experimental trend.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1990.     

Vortical regime of the flow behind the bow shock wave

A new nonstationary regime of the flow around a step and a cylinder was found to exist at high free-stream Mach numbers for gas specific heat ratios below 1.2. The main features of the flow are strong vortices in the shock-compressed region with supersonic reversal velocities at the body face. The bow shock wave takes on a complicated shape, fluctuating in time. The vortical regimes can result from local heterogeneities in the free stream. The case of the heterogeneity is studied in this paper in the form of a thin thermal layer of limited length. The vortical regime remains in existence after the source of disturbances is removed. The results have been obtained through computer simulations through the use of Eulerian hydrodynamic equations and by way of several numerical methods: FLIC, Godunov's scheme, TVD, and PPM. The influence of viscosity on the development of the vortical regime has been studied by computer solving the Navier–Stokes equations. Received 21 August 1998 / Accepted 6 June 2001     

FLAT-PLATE BOUNDARY-LAYER FLOWS INDUCED BY DUSTY SHOCK WAVE

ＦＬＡＴ－ＰＬＡＴＥＢＯＵＮＤＡＲＹ－ＬＡＹＥＲＦＬＯＷＳＩＮＤＵＣＥＤＢＹＤＵＳＴＹＳＨＯＣＫＷＡＶＥ（王柏懿）（陶锋）ＦＬＡＴ－ＰＬＡＴＥＢＯＵＮＤＡＲＹ－ＬＡＹＥＲＦＬＯＷＳＩＮＤＵＣＥＤＢＹＤＵＳＴＹＳＨＯＣＫＷＡＶＥ￥ＷａｎｇＢｏｙｉ；Ｔａ...     

激波诱导火焰失稳与爆轰的条件研究

采用九阶WENO和十阶中心差分格式数值求解激波与火焰作用过程,考察了激波强度、火焰尺寸对激波与球形火焰作用过程的影响。结果表明,增大激波强度或火焰尺寸均可在流场中引发爆轰,但激波强度的影响更大,并且其引发的爆轰可使火焰迅速膨胀,放热率提高,从而影响燃烧特性;此外,爆轰波传播过程中会迅速消耗可燃预混气,合并原有的反射激波,并在流场中形成局部高压区,极大地改变流场结构。