Reconsideration of inviscid shock interactions and transition phenomena on double-wedge geometries in a M ∞ = 9 hypersonic flow

Shock polar analysis as well as 2-D numerical computation technique are used to illustrate a diverse flow topology induced by shock/shock interaction in a M _∞ = 9 hypersonic flow. New flow features associated with inviscid shock wave interaction on double-wedge-like geometries are reported in this study. Transition of shock interaction, unsteady oscillation, and hysteresis phenomena in the RR ↔ MR transition, and the physical mechanisms behind these phenomena are numerically studied and analyzed.     

触摸高温气体动力学

回顾了高温气体动力学与高超声速科技相关的一些重要研究进展,探讨几个具有基础性研究意义的方向：即高超声速流动模拟;高温气体热化学反应机制;高超声速流动滞止区预测;高超声速边界层转捩和激波/激波相互作用诱导的气动热问题．这些研究方向与高温气体效应和强激波密切相关,对高超声速科技关键技术的突破起着重要作用．     

In the footsteps of Ernst Mach — A historical review of shock wave research at the Ernst-Mach-Institut

The aim of this paper is to recall some of the historical work on shock waves and to give a brief survey of research activities at the Ernst-Mach-Institut (EMI). Some fundamental results of Ernst Mach (1838 – 1916) are demonstrated and historical remarks are given to the shock tube as an important tool in shock wave research. The activity at EMI in this field was initiated by Prof. H. Schardin (1902 – 1965) in 1955 and has since been continued. Propagation processes of shock and blast waves, blast loading phenomena, shock attenuation, shock reflection at various surfaces, development of new types of blast simulators, electromagnetically driven T-tubes, precursor and decursor phenomena are only a few examples of research topics at EMI that will be discussed.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.     

Shock wave diffraction over a 90 degree sharp corner — Posters presented at 18th ISSW

A special poster session was run during the 18th International Symposium on Shock Waves, held on July 21 – 26, 1991, in Sendai, Japan. The purpose of this session was to compare various CFD schemes which are useful for simulating shock wave phenomena. A 2-D planar shock wave diffraction over a 90 degree sharp corner was selected as a bench mark problem. The problem specification and the output format are described below. Experimental outputs for the close flow conditions to the computational ones were also called for. Twenty six poster presentations were made at this session and the majority of the posters reflected a standard of excellence that warrants publication in the Shock Waves journal. Therefore these results are reproduced here. However, since there is a limit on the available page numbers, it was not possible to publish all the posters that were presented at the special poster session. We express our sincere thanks to all the participants in this session.     

The phenomena of shock wave reflection — a review of unsolved problems and future research needs

Although the phenomenon of shock wave reflection was discovered more than a hundred years ago, active research related to this phenomenon still goes on in many countries in the world (e.g., Australia, Canada, China, Germany, Israel, Japan, Poland, Russia and United States of America). As a matter of fact the research activity increased so drastically in the past decade and a half that a special scientific meeting dedicated to better understanding the reflection phenomena of shock waves, namely The International Mach Reflection Symposium was initiated in 1981 and was held since then in the major research centers actively involved in the research of shock wave reflections. In the present paper the status of the research of the phenomenon of shock wave reflection will be discussed in general, and unresolved problems and future research needs will be pointed out.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.     

Shock wave structure in a mixture of gas,vapour and droplets

The structure of the relaxation zone behind a shock wave of moderate strength in a mixture of gas, vapour and droplets is analysed. A model is presented for shock induced evaporation, which is based on wet-bulb equilibrium and on the absence of relative motion between droplets and gas. Experimental and numerical data on heterogeneous condensation induced by an unsteady rarefaction wave and on re-evaporation due to shock wave passage are reported for a mixture of water vapour, nitrogen gas and condensation nuclei. Pressure, temperature, saturation ratio and droplet size are experimentally obtained and are very well predicted by a numerical simulation based on the non-linear quasisteady wet-bulb model for phase transition, as well for the expansion wave as for the shock wave. During expansion, droplet number density decays much faster than predicted, which is not yet satisfactorily explained. Shock induced droplet evaporation is studied for post-shock saturation ratios ranging from 5×10^–3 to 0.2, corresponding to shock Mach numbers of 1.2 to 1.9. The evaporation times are well predicted by the theoretical model. No evidence is found for droplet break-up for Weber numbers up to 13, and droplet radii of the order of 1m.On leave at Institute of Fluid Science, Shock Wave Research Center, Tohoku University, Sendai 980, JapanThis article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Numerical investigation of inviscid shock wave dynamics in an expansion tube

Highly complicated shock wave dynamics has been numerically calculated by solving the Euler equations for a circular shock tube suddenly expanded three times of the original tube diameter atx=0. Shock waves of different shock Mach number,M _s =1.5 and 2.0, have produced remarkably distinct blast jet structures. A planar shock wave took its final form after the blast by repeated Mach reflections of the blast wave: the first one at the wall and the second one at the central axis. The central Mach disc overtook and merged with the annular Mach stem before the planar shock wave was formed. In contrast to the blast wave which would propagate spherically in an open space, the present blast wave undergoes complex morphological transformation in the restricted flow passage, resulting in an unstable and oscillatory blast jet structure of highly rotational nature. The slipstream tube emanating from the shock tube exit corner decomposed into a chain of small vortex rings that interacted with the barrel shock of the jet, which caused periodic collapse of the jet structure. The finite volume-FCT formulation equipped with the time-dependenth-refinement adaptive unstructured triangular mesh technique in the present paper has contributed to resolution of the intricate physical discontinuities developing in the blast flow fields.     

Oscillation modes of laval nozzle flow

Experimental investigations of Laval nozzle flow show for relatively low supply to exit pressure ratios, which correspond to shock wave positions close to the nozzle throat, three different, oscillatory instabilities.

1. Shock pattern oscillations where the root of a λ-like shock front remains nearly in constant position, but where the proportion between the normal part and the oblique part of the shock changes periodically.
2. Shock wave and separation bubble oscillations where the motion of the shock wave is accompanied by displacements of the separation bubble.
3. Flow rate oscillations where the shock waves leave periodically through the nozzle throat in upstream direction.

     

Summary of the 24th International Symposium on Shock Waves

The 24th International Symposium on Shock Waves (ISSW24) was held at the Beijing Friendship Hotel from July 11 to July 16, 2004, in Beijing, China, after a one-year delay due to the SARS outbreak in Beijing shortly before the Symposiums originally scheduled date in 2003. The event achieved success due to the continuous support and kind understanding from all the delegates and the International Advisory Committee. During the last three years, I have communicated constantly with so many people who encouraged me by providing their suggestions and advice whenever I was in need, from which I feel a sense of community: the community being full of friendship and understanding. It is very heart-warming to have such an experience and I am very happy to have served as chairman of the Symposium for such a community. On behalf of the Local Organizing Committee I would like to thank all of you for the contributions and help that you have given us, without which we would not have had the Symposium.After the announcement of the ISSW24 was sent out, the response from the international shock wave research community was very encouraging. A total of 460 abstracts were submitted to the ISSW24. Each of the abstracts was evaluated by three members of the Scientific Review Committee and the decision on acceptance was made based on the reviewers reports. 195 oral papers, including nine plenary lectures, were accepted to be presented in three parallel sessions, and 135 poster papers in three dedicated poster sessions. Topics discussed in these papers cover all aspects of shock wave research. Among the topics, supersonic and hypersonic aerodynamics; shock wave reflection, diffraction and focusing; and detonation phenomena and pulse detonation engines were the most popular. Such topics not only include interesting fundamental shock wave physics, but also have important application backgrounds. The plenary lectures of the ISSW24 were selected based on the recommendations from all the IAC members, and review the state of the art of the recent shock wave research. It was also found that a good number of papers were the result of international research collaboration. These facts have demonstrated that the ISSW24 is really international and scientific, and that shock wave research becomes an important research field of continuously increasing interest.The final programme consisted of eight plenary lectures, 123 oral papers and 75 poster papers. The total number is much smaller than that originally accepted due to the change of date, and even though this was chosen carefully, it still overlapped with other conferences, for example, the 24th International Symposium on Rarefied Gas Dynamics from July 10-14, 2004. There were 233 participants registered at ISSW24 from 20 countries and regions: Australia 9, Canada 11, China 58, France 8, Germany 14, India 21, Iran 1, Israel 7, Japan 57, Korea 2, Morocco 1, Netherlands 2, Norway 2, Russia 8, Singapore 3, South Africa 4, Chinese Taiwan 2, Thailand 1, UK 7, and USA 15.The Proceedings is a valuable resource because it brings the recent information of shock wave research together in one place, acts as an introduction to many researchers and students, and serves as a tool for promotion of the ISSW. This is the reason why the Local Organizing Committee works hard to manage to publish it. Two hundred and six papers in total are published in the final proceedings and are organized in such a way that all the papers relating to similar topics are grouped together. Both oral and poster papers are considered to be equal without making any distinction between them. The Proceedings are more comprehensive than the CD-ROM that all the participants received during the Symposium, which only contains the full papers that were received before June 15, 2004, and was intended as a tool for the prompt exchange of research information.The ISSW24 was delayed one year because of the SARS outbreak in Beijing last year. In keeping with the pattern set at the ISSW over the last 40 years, the International Advisory Committee of the ISSW24 has decided that the ISSW25 will be held in the year 2005. The organizer of the ISSW25 has been chosen by voting of all the IAC members at the end of the year 2002 to gain more time for the next organizer. Prof. K. P. J. Reddy from Indian Institute of Science has been selected to be the Chairman of the ISSW25. I sincerely express my congratulations to him and wish ISSW25 a success.We were greatly assisted in planning the ISSW24 by continuous support from various sponsors: the Chinese Academy of Sciences, the Nature Sciences Foundation of China, the Chinese Society of Shock Waves, the Chinese Society of Theoretical and Applied Mechanics and the Chinese Society of Aerodynamics. On behalf of the Local Organizing Committee, I would like thank all members of the International Advisory Committee for their guidance and suggestions, and the Scientific Review Committee for their careful and efficient evaluation of the abstracts. My greatest thanks have to be to the delegates for providing high quality papers and actively participating in the Symposium. For editorial assistance, I wish to thank Dr. C. Wang for re-editing all the papers according to the required style of the ISSW24, and for compiling these proceedings. I must also thank Miss Q. Pu and X. Wang, my secretaries, for taking care of so many details in organizing the Symposium. Many thanks also go to the staff and students of the Key Laboratory of High Temperature Gas Dynamics, the Institute of Mechanics, Chinese Academy of Sciences for helping and supporting me over the past three years. Finally, I want to express my appreciation to Dr. Chris Caron from Springer-Verlag for his kind cooperation in publishing these proceedings.Received: 30 November 2004, Accepted: 30 November 2004, Published online: 24 February 2005[/PUBLISHED]Zonglin Jiang: Chairman of the ISS24Correspondence to: Zonglin Jiang     

Shock Hugoniot for Biological Materials

This paper presents shock Hugoniot compression data for several bio-related materials by using flat plate impact experiments. Shock pressure covered in this study ranges at least up to 1 GPa. It is emphasized here that spatial and temporal uniformity of pressure distribution behind a shock wave front is very important and it can be realized in these materials by the impact method, and their precise shock propagation characteristics have been obtained by the application of the procedure developed previously by our group. Hugoniot measurements for different and systematic data for various samples are compared with shock Hugoniot curve for water. Samples used in the experiment include water gel of gelatin, NaCl aqueous solution, and finally chicken breast meat. Several samples with different initial density were used for gelatin and NaCl solution. Shock Hugoniot function for all the specimens tested can be summarized as u _s =A+B u _p , B ~ 2Value of the intercept of the relationship, A, which has the meaning of the sound velocity, is apparently dependent on the material and ambient temperature. Physical meanings of the obtained results have been discussed.     

Visualization of shock-wave formation processes during shock reflection at obstacles with multiple steps

According to standard textbooks on compressible fluid dynamics, a shock wave is formed by an accumulation of compression waves. However, the process by which an accumulated compression wave grows into a shock wave has never been visualized. In the present paper, the authors tried to visualize this process using a model wedge with multiple steps. This model is useful for generating a series of compression waves and can simulate a compression process that occurs in a shock tube. By estimating the triple-point trajectory angle, we demonstrated visually that an accumulated compression wave grows into a shock wave. Further reflection experiments over a rough-surface wedge confirmed the tendency for the triple point trajectory angle to reach the asymptotic value _s in the end.This work was first presented at the Symposium on Shock Waves, Japan 2002     

Axisymmetric shock wave interaction with a cone: a benchmark test

Results of the benchmark test are presented of comparing numerical schemes solving shock wave of M_s = 2.38 in nitrogen and argon interacting with a 43∘ semi-apex angle cone and corresponding experiments. The benchmark test was announced in Shock Waves Vol. 12, No. 4, in which we tried to clarify the effects of viscosity and heat conductivity on shock reflection in conical flows. This paper summarizes results of ten numerical and two experimental applications. State of the art in studies regarding the shock/cone interaction is clarified. PACS 01.50.Kw, 47.15.Pn Communicated by K. Takayama     

Attenuation of shock waves propagating in polyurethane foams

Shock wave attenuation in polyurethane foams is investigated experimentally and numerically. This study is a part of research project regarding shock propagation in polyurethane foams with high-porosities = 0.951 ~ 0.977 and low densities of ρc = 27.6 ~55.8 kg/m³. Sixty Millimeter long cylindrical foams with various cell numbers and foam insertion condition were installed in a horizontal shock tube of 50 mm i.d. and 5.4 mm in length. Results of pressure measurements in air/foam combination are compared with CFD simulation solving the one-dimensional Euler equations. In the case of a foam B fixed on shock tube wall, pressures at the shock tube end wall increases relatively slowly comparing to non-fixed foam, free to move and a foam A fixed on shock tube wall. This implies that elastic inertia hardly contributes to pressure build up. Pressures behind a foam C fixed on shock tube wall decrease indicating that shock wave is degenerated into compression wave. Dimensionless impulse and attenuation factor decrease as the initial cell number increases. The momentum loss varies depending on cell structure and cell number.     

Experimental study of the shock–bubble interaction with reshock

The interaction of a planar shock wave with a spherical density inhomogeneity is studied experimentally under reshock conditions. Reshock occurs when the incident shock wave, which has already accelerated the spherical bubble, reflects off the tube end wall and reaccelerates the inhomogeneity for a second time. These experiments are performed at the Wisconsin Shock Tube Laboratory, in a 9m-long vertical shock tube with a large square cross section (25.4×25.4 cm²). The bubble is prepared on a pneumatically retracted injector and released into a state of free fall. Planar diagnostic methods are used to study the bubble morphology after reshock. Data are presented for experiments involving two Atwood numbers (A = 0.17 and 0.68) and three Mach numbers (1.35 < M < 2.33). For the low Atwood number case, a secondary vortex ring appears immediately after reshock which is not observed for the larger Atwood number. The post-reshock vortex velocity is shown to be proportional to the incident Mach number, M, the initial Atwood number, A, and the incident shock wave speed, W _i.     

In memoriam Dr. Werner Heilig (1933-2003)

A dear friend and colleague, Dr. Werner Heilig, died last December (2-12-2003) after a short and painful illness. Dr. Heilig was well known and respected in the world-wide shock wave family due to his contributions to our understanding of shock reflection and interaction phenomena.Dr. Werner Heilig was born in Freiburg in January 1933. He received his matriculation from the Kepler-Gymnasium in Freiburg in 1953 and immediately thereafter started studying Mathematics and Physics at the Albert-Ludwigs University in Freiburg, from which he graduated in early 1958. After graduation he took an extra two years of pedagogy studies in order to qualify as a teacher of mathematics in a high school (Gymnasium), and indeed he served as a mathematics teacher in a Gymnasium from January 1961 until March 1964. A big change in his professional career took place in April 1964 when he joined the Ernst-Mach-Institute in Freiburg. Simultaneously with his new work at the Ernst-Mach-Institute he was teaching every morning from 8 to 9 oclock mathematics at the St. Ursula Gymnasium, walking to his new place of work immediately after teaching. At that time he also started his PhD studies at the University of Karlsruhe. The title of his thesis was: Theoretical and experimental studies of shock wave interaction with a sphere and a cylinder (Theoretische und experimentelle Untersuchungen zur Beugung von Stosswellen an Kugeln und Zylindern). Dr. Heilig continued this investigation, as well as other related topics, throughout his professional career. His PhD research was co-supervised by Professors Zierep and Oertel and the degree was granted in July 1969. In his dissertation he also discussed the transition criteria from regular to Mach reflection for shock wave reflection from wedges or cylinders (as is evident from Fig. 13 in his dissertation). However, since his results were not published in a reviewed journal, he has not received the credit he duly deserved.After receiving his PhD degree, Dr. Heilig started building his reputation as a careful and reliable researcher in gas dynamics, focusing his attention on shock wave reflection from wedges, shock and blast wave propagation in ducts and tunnels, and shock wave interaction with boundaries of various shapes. Until the mid 1980s most of his work was experimental, that being the strong side of the Ernst-Mach-Institute at the time. In early 1984 Dr. Heilig was assigned to introduce CFD to the Ernst-Mach-Institute. This move forced him to go from being an experimentalist to a CFD researcher, which proved to be very demanding. However, Dr. Heilig did it well, relying on his mathematical skills earned as a student in the 1950s. From the mid 1980s on he was the head of the gas dynamics group at the Ernst-Mach-Institute, and in January 1997 he became the vice-director of the Ernst-Mach-Institute, a position he held until his retirement in February 1998. Once free from formal obligations, he avidly continued his research activities, submitting proposals for (and receiving) research contracts, and writing the chapter on shock wave propagation in ducts and tunnels in the Handbook of Shock Waves which was published in 2000 by Academic Press.I first met Dr. Heilig when he attended the 12th Shock Waves Symposium, which was held in Jerusalem in July 1979, and we kept in touch ever since. We jointly proposed and conducted research on various aspects of shock wave interaction with bodies of numerous shapes, and co-authored several papers based on the results of our joint-research. It was a pleasure working with Dr. Heilig; he was a very careful scientist who was never fazed by challenging problems. His untimely death has shocked and saddened us all. May the emptiness left in our hearts by his departure be filled by gentle memories of Dr. Werner Heilig, an outstanding researcher, colleague and friend.Published online: 18 February 2005[/PUBLISHED]     

Phase step holographic interferometry applied to hypervelocity,non-equilibrium cylinder flow

For blunt bodies the reduced bow shock wave stand-off distance and the shock layer density rise in the stagnation region as compared to ideal gas flow are phenomena caused by dissociative effects. In this work experiments with aR _BODY=45 mm radius cylinder and an aspect ratio ofL/R _BODY 11 are described. The tests were carried out in the High Enthalpy Shock Tunnel in Göttingen (HEG), a free piston driven shock tunnel. Two different test conditions at reservoir enthalpies of around 21 MJ/kg and Mach numbers of around 9 in air and nitrogen were available.Optical measurements with a holographic phase step interferometer to obtain complete flow field density gradients have been carried out. By increasing the signal-to-noise ratio with the technique of phase stepping over the original recording quality, high quality interferograms are obtained. The high spatial resolution of the holograms results in the creation of hologram-schlieren images which are compared to directly recorded laser-schlieren images.Infinite and finite fringe interferograms and the complete density fields for the two free-stream conditions are presented. The stagnation line densities are quantified. The measured results are shown and compared with Navier-Stokes calculations which account for chemical reactions in the flow. The numerical code underpredicts the stand-off distance of the bow shock wave. It is shown that the flow behind the bow shock wave is in non-equilibrium and that it reaches equilibrium before the body for one condition.This work was an offshoot of an ESA research contract monitored by Dr. D. Vennemann, whose support is gratefully acknowledged. This study of stagnating high enthalpy flows has exceedingly benefited from discussions with S. Brück and V. Hannemann. The operation of the large wind tunnel HEG is the result of a team effort. The with to thank the whole team, represented by Dr. W.H. Beck, for keeping the tunnel going.     

Interaction of a shock with a sphere suspended in a vertical shock tube

Shock wave interaction with a sphere is one of the benchmark tests in shock dynamics. However, unlike wind tunnel experiments, unsteady drag force on a sphere installed in a shock tube have not been measured quantitatively. This paper presents an experimental and numerical study of the unsteady drag force acting on a 80 mm diameter sphere which was vertically suspended in a 300 mm x 300 mm vertical shock tube and loaded with a planar shock wave of M _s = 1.22 in air. The drag force history on the sphere was measured by an accelerometer installed in it. Accelerometer output signals were subjected to deconvolution data processing, producing a drag history comparable to that obtained by solving numerically the Navier-Stokes equations. A good agreement was obtained between the measured and computed drag force histories. In order to interpret the interaction of shock wave over the sphere, high speed video recordings and double exposure holographic interferometric observations were also conducted. It was found that the maximum drag force appeared not at the time instant when the shock arrived at the equator of the sphere, but at some earlier time before the transition of the reflected shock wave from regular to Mach reflection took place. A negative value of the drag force was observed, even though for a very short duration of time, when the Mach stem of the transmitted shock wave relfected and focused at the rear stagnation point of the sphere.Received: 31 March 2003, Accepted: 7 July 2003, Published online: 2 September 2003     

新型复合炸药DN-1的能量输出特性与低易损性研究

为实现兼具高能量输出与低易损性两方面的要求,研发了一种以2,4-二硝基苯甲醚(DNAN)为载体的复合炸药DN-1.用爆炸压力测试系统研究了DN-1炸药的能量输出特性,并用隔板实验测试了DN-1的冲击波感度.结果表明,DN-1炸药的冲击波超压峰值是TNT的1.6倍,冲击波比能是TNT的1.67倍,冲击波感度L50=7.64mm.其综合性能优于TNT等传统炸药.     

Cavitation phenomena in extracorporeal microexplosion lithotripsy

An experimental investigation was made of cavitation phenomena induced by underwater shock wave focusing applied to the extracorporeal microexplosion lithotripsy (microexplosion ESWL). Firstly an underwater microexplosion generated by detonation of a 10 mg silver azide pellet was studied and secondly underwater shock focusing and its induced cavitation phenomena were investgated. Underwater shock wave was focused by using a semi-ellipsoidal reflector in which a shock wave generated at the first focal point of the reflector was reflected and focused at the second focal point. It is found that an explosion product gas bubble did not produce any distinct rebound shocks. Meantime cavitation appeared after shock focusing at the second focal point where expansion waves originated at the exit of the reflector were simultaneously collected. A shock/bubble interaction is found to contribute not only to urinary tract stone disintegration but also tissue damage. The cavitation effect associated with the microexplosion ESWL was weaker in comparison with a spark discharge ESWL. The microexplosion ESWL is an effective method which can minimize the number of shock exposures hence decreasing tissue damage by conducting precise positioning of urinary tract stones.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.     

Molecular gas dynamics applied to phase change processes at a vapor–liquid interface: shock-tube experiment and MGD computation for methanol

This paper deals with a molecular gas-dynamics method applied to the accurate determination of the condensation coefficient of methanol vapor. The method consisted of an experiment using a shock tube and computations using a molecular gas-dynamics equation. The experiments were performed in such situations where the shift from a vapor–liquid equilibrium state to a nonequilibrium one is realized by a shock wave in a scale of molecular mean free time of vapor molecules. The temporal evolution in thickness of a liquid film formed on the shock-tube endwall behind a reflected shock wave is measured by an optical interferometer. By comparing the measured liquid-film thickness with numerical solutions for a polyatomic version of the Gaussian–BGK model of the Boltzmann equation, the condensation coefficient of methanol vapor is accurately determined in vapor–liquid nonequilibrium states. As a result, it is clear that the condensation coefficient is just unity very near to an equilibrium state, but is smaller far from the equilibrium state.