Advances in detonation driving techniques for a shock tube/tunnel

Early works on the detonation driven shock tube are reviewed briefly. High initial pressure detonable mixture can be used in backward-detonation driver when the buffer tube is attached to the end of the driver for eliminating the excessive reflected peak pressure. Experimental data showed that an improvement on attenuation of the incident shock wave generated by the forward driver can be obtained, provided the diameter of the driver is larger than that of the driven section and an abrupt reduction of cross-section area is placed just beyond the diaphragm. Also, it is clearly verified by a numerical analysis. An additional backward-detonation driver is proposed to attach to the primary detonation driver and on condition that the ratios of initial pressure in the additional driver to that in the primary driver exceed the threshold value, the Taylor wave behind detonation wave in the primary detonation driver can be eliminated completely.     

氢氧燃烧及爆轰驱动激波管

分析并观察了沿驱动段轴向分布多火塞燃烧驱动段的性能．提出主膜处同一管截面均匀分布三火花塞引燃的点火方法．用这种点火方法驱动产生的入射激波强度重复性较高,激波后气流速度、温度和压力的定常性亦大大改善,可满足气动试验实际要求．提出在驱动段尾端串接卸爆段来消除爆轰波反射高压,从而可使反向爆轰驱动段用来产生高焓高密度试验气流．这种反向爆轰驱动产生的入射激波重复性高,激波衰减弱．在主膜处的收缩段产生的反射波可缓解爆轰波后跟随的稀疏波的不利影响,从而使前向爆轰驱动具有实用性．在产生的入射激波强度相同条件下,前向爆轰驱动所需的爆轰驱动段可爆混合气初始压力可较反向爆轰低近一个量级．     

探索发展激波风洞爆轰驱动技术

发现了燃烧驱动激波管中入射激波马赫数异常升高的起因. 实验显示爆轰驱动能力强于燃烧驱动, 从而推动爆轰驱动技术的发展. 采用卸爆管消除爆轰波反射高压以及双爆轰驱动段全部消除爆轰波后的Taylor稀疏波, 使反向和前向爆轰驱动模式具有实用价值. 反向爆轰驱动技术还成功用来延长激波风洞试验时间.      

One-dimensional shock wave interaction with rubber and low-porosity foam

One-dimensional interaction between a planar shock wave and a rubber or low-porosity foam is investigated experimentally and numerically. The considered polyurethane foam is of high density (ρ _c=290 kg/m³) and lowporosity (ϕ=0.76), and this corresponds to an intermediate condition between rubber and high-porosity foam. Stress-strain relations for the low-porosity foam are investigated by machine tests, which show larger deformation against compressive force and higher non-linearity in stress-strain curve as compared with rubber. Also the low-porosity foam shows a hysteresis cycle. Experiments on shock wave-foam interactions are conducted by using a shock tube. Experimental time history of the surface stress of the foam at the end of the shock tube does not show shock type stress increase, but continuous excessive stress rise can be seen, and then dumping vibration approaching to gas dynamic pressure of the reflected shock wave is followed, and the highest stress amounts about 3∼4 times of the pressure after the reflected gas dynamic shock wave. Interactive motions of gas and the low-porosity foam are analyzed using the Lagrangean coordinates system. An elastic model for a low-porosity foam is assumed to be a single elastic material with the measured stress-strain relation. Results of numerical simulations are compared with the shock tube experiments, which show essentially same stress variations with experimental results.     

Simulation of a complete reflected shock tunnel showing a vortex mechanism for flow contamination

Simulations of a complete reflected shock tunnel facility have been performed with the aim of providing a better understanding of the flow through these facilities. In particular, the analysis is focused on the premature contamination of the test flow with the driver gas. The axisymmetric simulations model the full geometry of the shock tunnel and incorporate an iris-based model of the primary diaphragm rupture mechanics, an ideal secondary diaphragm and account for turbulence in the shock tube boundary layer with the Baldwin-Lomax eddy viscosity model. Two operating conditions were examined: one resulting in an over-tailored mode of operation and the other resulting in approximately tailored operation. The accuracy of the simulations is assessed through comparison with experimental measurements of static pressure, pitot pressure and stagnation temperature. It is shown that the widely-accepted driver gas contamination mechanism in which driver gas ‘jets’ along the walls through action of the bifurcated foot of the reflected shock, does not directly transport the driver gas to the nozzle at these conditions. Instead, driver gas laden vortices are generated by the bifurcated reflected shock. These vortices prevent jetting of the driver gas along the walls and convect driver gas away from the shock tube wall and downstream into the nozzle. Additional vorticity generated by the interaction of the reflected shock and the contact surface enhances the process in the over-tailored case. However, the basic mechanism appears to operate in a similar way for both the over-tailored and the approximately tailored conditions.Communicated by R. R. Boyce     

双驱动激波管稀疏波破膜技术研究

本文介绍了在双驱动激波管中运用稀疏波破膜的技术。在以压缩空气和氮气作实验气体的情形下,实验研究了中间段长度、稀疏波强度及中间段B膜的破膜压力（压差）对第二激波追韩第一激波的影响。实验结果表明：中间段的长短,显著地制约着前后两道激波的间隔;稀疏波强度及中间段B膜的破膜压力对稀疏波破膜时间及第二激小对反射稀疏波的追赶有重要影响。     

Macro-mechanical modeling of blast-wave mitigation in foams. Part II: reliability of pressure measurements

A phenomenological study of the process occurring when a plane shock wave reflected off an aqueous foam column filling the test section of a vertical shock tube has been undertaken. The experiments were conducted with initial shock wave Mach numbers in the range $1.25\le {M}_\mathrm{s} \le 1.7$ and foam column heights in the range 100–450 mm. Miniature piezotrone circuit electronic pressure transducers were used to record the pressure histories upstream and alongside the foam column. The aim of these experiments was to find a simple way to eliminate a spatial averaging as an artifact of the pressure history recorded by the side-on transducer. For this purpose, we discuss first the common behaviors of the pressure traces in extended time scales. These observations evidently quantify the low frequency variations of the pressure field within the different flow domains of the shock tube. Thereafter, we focus on the fronts of the pressure signals, which, in turn, characterize the high-frequency response of the foam column to the shock wave impact. Since the front shape and the amplitude of the pressure signal most likely play a significant role in the foam destruction, phase changes and/or other physical factors, such as high capacity, viscosity, etc., the common practice of the data processing is revised and discussed in detail. Generally, side-on pressure measurements must be used with great caution when performed in wet aqueous foams, because the low sound speed is especially prone to this effect. Since the spatial averaged recorded pressure signals do not reproduce well the real behaviors of the pressure rise, the recorded shape of the shock wave front in the foam appears much thicker. It is also found that when a thin liquid film wet the sensing membrane, the transducer sensitivity was changed. As a result, the pressure recorded in the foam could exceed the real amplitude of the post-shock wave flow. A simple procedure, which allows correcting this imperfection, is discussed in detail.     

A chemical shock tube driven by detonation

A chemical shock tube driven by a detonation driver is described in the present paper. This shock tube can produce a single controlled high-temperature pulse for studies of gas-phase reaction kinetics, but the difficulty associated with the timing for the rupture of diaphragms in the conventional chemical shock tube is overcome, because the detonation wave in the driver section can be predicted correctly and shows a good repeatability. In addition, this shock tube is capable of providing higher temperature conditions for the test gas than the conventional high-pressure shock tube, owing to the inherently high-driving capability of the detonation driver. The feasibility of this shock tube is examined by numerical simulations and preliminary experiments.     

Fracture Evaluation in a Ceramic Spherical Dome Port Under Shock Impact

In this study, a fracture evaluation of a ceramic spherical dome port under shock impact has been presented. The experiments were carried out with a shock tube device capable to produce a normal shock. The pressure behind the normal and reflected shock wave was predicted by analytic equations based on initial conditions. The pressures were measured by embedded dynamic pressure sensors. The fracture of specimen was occurred by the pressure behind the reflected shock wave. The pressure distribution in shock tube was obtained during 0 to 5 ms. Simultaneously, the distributions of the pressure, temperature and velocity were calculated in the shock tube at 3 ms after diaphragm burst for various thickness of dome port. The results of numerical analysis and analytic solutions were good agreement with experimental results.     

Diffraction and re-initiation of detonations behind a backward-facing step

Diffraction phenomena of gaseous detonation waves behind a backward-facing step in a tube are observed by using high-speed schlieren photography and soot-track records as well as by pressure measurements on the sidewall. Mixtures are stoichiometric oxyhydrogen and those diluted by argon at sub-atmospheric pressures. Three types of phenomena are observed, that is, continuous propagation of detonation, re-initiation after a temporal extinction of detonation and complete extinction of detonation. The continuous propagation means that the diffracted wave does not affect the main propagation although reflected shock waves from the bottom surface of the tube may affect it. The re-initiation occurs at a wall surface of the tube behind a reflected shock wave after the main detonation wave has been extinguished. Positions and conditions of the re-initiation are discussed. The complete extinction is defined as disappearance of detonation cells behind the step within a certain length of the tube. Cases exist where an ignition occurs after several reflections off the bottom and top surface of the tube.     

Detonation formation in H $_2$-O $_2$/He/Ar mixtures at elevated initial pressures

In this paper the formation of detonation in H-O/He/Ar mixtures at elevated initial pressures was investigated in an initiation tube for a detonation driver with an exploding wire as the ignition source. In most experiments the detonation wave was formed by a DDT process in which a reactive shock wave accelerates behind the leading shock wave and eventually leads to the onset of detonation. The onset position was found to be at the leading shock wave or behind it. Only in very sensitive mixtures at high initial pressure the direct initiation of detonation was observed. The influence of ignition energy, initial pressure and composition on the detonation induction distance was determined. The results show that the detonation induction distance increases with the decrease of ignition energy and initial pressure and with the increase of the mole fraction of helium or argon. With the same mole fraction, argon increases the induction distance more than helium. In the facility utilized the DDT upper and lower limits of hydrogen in H-O mixtures are in the ranges from 36 to 40 % and from 78 to 82 %, respectively, and the upper limits for helium and argon in stoichiometric H-O mixtures are 40 % and 36 %, respectively. High pressure peaks generated by the DDT process were measured, especially in mixtures near the DDT limits. Statistical results show that such peak pressures can be up to 6 times of the CJ-pressures. Received 1 March 2000 / Accepted 25 May 2000     

The unsteadiness of shock waves propagating through gas-particle mixtures

A shock wave which is incident onto a gas-particle mixture or initiated within such a mixture needs a certain distance to reach a constant velocity. This effect is due to the inertia and the heat capacity of the particles. In general the shock wave is decelerated and the frozen pressure jump is decaying. A vertical shock tube was used in order to produce a plane shock wave incident onto a homogeneous gas-particle mixture. In addition to measurements of the shock velocity and the pressure history along the total low pressure section, the particle velocity was measured within the relaxation zone far downstream of the diaphragm using a laser-Doppler-velocimeter. Thus a drag law describing the particle acceleration within the relaxation zone was derived from the measurements. To compare the experiments with theoretical results, calculations were performed by the random-choice method.     

Characteristics of an annular vertical diaphragmless shock tube

Abstract. This paper reports on the characteristics of a compact vertical diaphragmless shock tube, which was constructed and tested in the Shock Wave Research Center to study experimentally the behavior of toroidal shock waves. It is 1.15 m in height and has a self-sustained co-axial vertical structure consisting of a 100 mm i.d. outer tube and an 80 mm o.d. inner tube. To create a ring shaped shock wave between the inner and outer tubes, a rubber sheet is inserted to separate a high pressure driver gas from a test gas, which is bulged with auxiliary high pressure helium from the behind. When the rubber membrane is contracted by the sudden release of the auxiliary gas so as to break the seal, shock waves are formed. Special design features of the shock tube are described and their role in producing repeatable shock waves is discussed. Its special opening characteristics make possible the production of annular shaped shock waves that are unlikely met with a conventional tube that uses rupturing diaphragms. Performance of the shock tube is evaluated in terms of the shock wave Mach numbers and the measured flow properties. It eventually showed a higher degree of repeatability and the scatter in the shock wave Mach numbers Ms was found to be 0.2% for Ms ranging from 1.1 to 1.8. The shock wave Mach number so far measured agreed very well with the simple shock tube theory. Received 3 February 1999 / Accepted 6 April 2000     

Reconstruction of velocity fields from wall pressure measurements in a shock wave/turbulent boundary layer interaction

We present here experimental results in a shock wave/turbulent boundary layer interaction at Mach number of 2.3 impinged by an oblique shock wave, with a deflection angle of 9.5°, as installed in the supersonic wind tunnel of the IUSTI laboratory, France. For such a shock intensity, strong unsteadiness are developing inside the separated zone involving very low frequencies associated with reflected shock motions.The present work consists in simultaneous PIV velocity fields and unsteady wall pressure measurements. The wall pressure and PIV measurements were used to characterize the pressure distribution at the wall in an axial direction, and the flow field associated. These results give access for the first time to the spatial-time correlation between wall pressure and velocity in a shock wave turbulent boundary layer interaction and show the feasibility of such coupling techniques in compressible flows. Linear Stochastic Estimation (LSE) coupled with Proper Orthogonal Decomposition (POD) has been applied to these measurements, and first results are presented here, showing the ability of these techniques to reproduce both the unsteady breathing of the recirculating bubble at low frequency and the Kelvin–Helmholtz instabilities developing at moderate frequency.     

A New Shock Tube Facility for Tunnel Safety

In this paper, a new double diaphragm shock tube facility for studying the structural response of a circular plate resting on soil, when subjected to a shock wave, is described. The present shock tube has been designed in the framework of a more extensive research program aimed at the investigation of underground tunnel lining under blast and fire conditions. The innovative features of the facility are an end-chamber conceived to investigate soil-structure interaction and a burner equipment to heat the specimen in order to study to what extent thermal damage can affect the transmitted and reflected pressure wave as well as the structural response. Details of the shock tube design, construction and test procedure operations are discussed in the paper. Particular emphasis is placed on the principles that have driven the experimental equipment design choices. Numerical simulations have been performed to assess the ideal shock tube performance in terms of reflected pressure and test time duration as well as to evaluate how far the fire testing situation actually is from that normally used in tunnel design.     

Experimental study of toroidal shock wave focusing in a compact vertical annular diaphragmless shock tube

The paper reports results of experiments regarding toroidal shock wave focusing in a vertical shock tube as a part of a series of converging shock wave studies. This compact vertical shock tube was designed to achieve a high degree of reproducibility with minimum shock formation distance by adopting a diaphragmless operating system. The shock tube was manufactured in the Institute of Fluid Science, Tohoku University. An aspheric lens shaped cylindrical test section was connected at the open end of the shock tube to visualize the diffraction and focusing of the toroidal shock wave released from the ring shaped shock tube opening. Pressure transducers were flush mounted on the shock tube’s test section to measure pressure histories at the converging test section. Double exposure holographic interferometry was employed to quantitatively visualize the shock waves. The whole sequence of toroidal shock wave diffraction, focusing, and its reflection from the symmetrical axis were successfully studied. The transition of reflected shock waves was observed.     

一种新的运动激波--非定常边界层相互干扰现象

本文探讨了一种新的激波－非定常边界层相互干扰现象，这种激波－边界层干扰现象既不同于定常激波－边界层干扰现象，又不同于激波在端面反射后与该激波所诱导的边界层之间的干扰现象，而是运动激波与稀疏波和第一激波所诱导的非这常边界层之间的干扰现象，本文对这种现象用微波动力学理论进行分析，并把这种干扰现象看成激波的绕射现象，同时在稀疏波破膜的双驱动激波管中进行实验观察，最后把理论分析与实验观察进行了比较。     

The effects that changes in the diaphragm aperture have on the resulting shock tube flow

In a conventional shock tube, the driver and the driven sections have similar (if not identical) cross-sectional area and the diaphragm opened area, upon rupturing, is practically equal to the tube cross-sectional area. Such geometry results in generating a well-formed shock wave in the tube’s driven section. The present experimental work checks the effects that changes in the diaphragm ruptured area have on the generated shock and rarefaction waves. Experiments were conducted in an 80?mm by 80?mm cross section shock tube generating incident shock waves having Mach numbers within the range from 1.06 to 1.25. In each run, pressure histories were recorded along the driven and the driver sections of the shock tube. The recorded pressures reveal that progressive reduction in the diaphragm open space resulted in a weaker shock and both longer time and distance until the compression waves generated close to the diaphragm coalesces into a shock wave. In addition, reducing the open space of the diaphragm resulted in a significant slow down in the high pressure reduction prevailing in the driver section.     

Detonation driver for enhancing shock tube performance

The development of a shock-induced detonation driver for enhancing the performance of a shock tube is described. The detonation wave is induced by the expansion of helium or air. Various gaseous fuel-oxidizer combinations are examined. This method produces a detonation wave which propagates downstream that transitions into a shock wave in the driven section. High-enthalpy flows with a maximum total temperature of 4200 K and a maximum total pressure of 34 atm in the driven tube are achieved. The problems of achieving the so-called perfectly-driven mode as well as those of inadequate fuel-oxidizer mixing are discussed.Received: 26 April 2002, Accepted: 23 December 2002, Published online: 28 April 2003     

Destruction of mouse lymphoma cells with high pressure pulses generated by a diaphragmless shock tube

A high pressure pulse, which was produced by a shock tube, was hit repeatedly on a pellet of mouse EL-4 T-lymphoma cells packed in a small test tube which was filled up with culture medium. The pressure pulse measured at the conical bottom of the tube had about 30 μs width and up to 8.4 MPa height depending on the driver gas pressure of the shock tube. The lymphoma cells began to be destroyed by hitting with 100 pulses having a peak pressure around 3 MPa. The fraction of dead cells in the tube exposed to the shock wave of 100 pulses rose exponentially as the peak pressure was increased from 3 MPa to 8 MPa. The fraction of dead cells at 6.0 MPa of the peak pressure was around 10%. However, proliferative function of the cells survived after exposure to 6.0 MPa-peak-pressure pulses seemed intact because the cells which survived the exposure proliferated as well as the nonexposed control cells.