Conventional Shock Tube Research Articles

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.

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.

Computational Study on Micro Shock Tube Flows with Gradual Diaphragm Rupture Process

Gas flows through micro shock tubes are widely used in many engineering applications such as micro engines, particle delivery devices etc. Recently, few studies have been carried out to explore the shock wave excursions through micro shock tubes at very low Reynolds number and at rarefied gas condition. But these studies assumed centered shock and expansion waves, which are generally produced by instantaneous diaphragm rupture process. But in real scenario, the diaphragm ruptures with a finite rupture time and this phenomenon will significantly alter the shock wave propagation characteristics. In the present research, numerical simulations have been carried out on a two dimensional micro shock tube model to simulate the effect of finite diaphragm rupture process on the wave characteristics. The rarefaction effect was simulated using Maxwell’s slip wall equations. The results show that shock wave attenuates rapidly in micro shock tubes compared to conventional macro shock tubes. Finite diaphragm rupture causes the formation of non-centered shock wave at some distance ahead of the diaphragm. The shock propagation distance is also drastically reduced by the rupture effects.

Theoretical–experimental study of shock wave-assisted metal forming process using a diaphragmless shock tube

The use of high-velocity sheet-forming techniques where the strain rates are in excess of 102/s can help us solve many problems that are difficult to overcome with traditional metal-forming techniques. In this investigation, thin metallic plates/foils were subjected to shock wave loading in the newly developed diaphragmless shock tube. The conventional shock tube used in the aerodynamic applications uses a metal diaphragm for generating shock waves. This method of operation has its own disadvantages including the problems associated with repeatable and reliable generation of shock waves. Moreover, in industrial scenario, changing metal diaphragms after every shot is not desirable. Hence, a diaphragmless shock tube is calibrated and used in this study. Shock Mach numbers up to 3 can be generated with a high degree of repeatability (±4 per cent) for the pressure jumps across the primary shock wave. The shock Mach number scatter is within ±1.5 per cent. Copper, brass, and aluminium plates of diameter 60 mm and thickness varying from 0.1 to 1 mm are used. The plate peak over-pressures ranging from 1 to 10 bar are used. The midpoint deflection, circumferential, radial, and thickness strains are measured and using these, the Von Mises strain is also calculated. The experimental results are compared with the numerical values obtained using finite element analysis. The experimental results match well with the numerical values. The plastic hinge effect was also observed in the finite element simulations. Analysis of the failed specimens shows that aluminium plates had mode I failure, whereas copper plates had mode II failure.

Experimental technique for generating fast high-density shock waves with phased linear explosive shock tubes

The sequential detonation of a layer of explosive surrounding a pressurized tube can be used to generate fast, high-density shock waves by means of a piston-like implosive pinch travelling at the detonation velocity of the explosive. A novel technique has been developed to extend the regime of operation to piston velocities greater than the detonation velocity of known explosives. This technique consists of cutting a slit in the tamper of a conventional explosive shock tube and introducing a phased detonation wave into the explosive cladding. Preliminary results indicate that quasi-steady shocks can be generated in helium with velocities between 13–17 km/s for initial fill pressures of 6.9 MPa.

A shock tube with a high-repetition-rate time-of-flight mass spectrometer for investigations of complex reaction systems

A conventional membrane-type stainless steel shock tube has been coupled to a high-repetition-rate time-of-flight mass spectrometer (HRR-TOF-MS) to be used to study complex reaction systems such as the formation of pollutants in combustion processes or formation of nanoparticles from metal containing organic compounds. Opposed to other TOF-MS shock tubes, our instrument is equipped with a modular sampling unit that allows to sample with or without a skimmer. The skimmer unit can be mounted or removed in less than 10 min. Thus, it is possible to adjust the sampling procedure, namely, the mass flux into the ionization chamber of the HRR-TOF-MS, to the experimental situation imposed by species-specific ionization cross sections and vapor pressures. The whole sampling section was optimized with respect to a minimal distance between the nozzle tip inside the shock tube and the ion source inside the TOF-MS. The design of the apparatus is presented and the influence of the skimmer on the measured spectra is demonstrated by comparing data from both operation modes for conditions typical for chemical kinetics experiments. The well-studied thermal decomposition of acetylene has been used as a test system to validate the new setup against kinetics mechanisms reported in literature.

Shock tube ignition delay time measurements in propane/O2/argon mixtures at near-constant-volume conditions

Shock tube measurements of ignition delay times with high activation energies are strongly sensitive to variations in reflected shock temperatures. At longer shock tube test times, as are needed at low reaction temperatures, small gradual increases in pressure (and simultaneous increases in temperature) that result from incident shock wave attenuation and boundary layer growth can significantly shorten measured ignition delay times. To obviate this pressure increase, we made use of a recently developed driver-insert method of Hong et al. [8] that allows generation of near-constant-volume test conditions for reflected shock measurements. Using this method, we have measured propane ignition delay times in a lean mixture (0.8% C3H8/8% O2/Ar) over temperatures between 980 and 1400K and nominal pressures of 6, 24 and 60atm, under both conventional shock tube operation (with post-shock fractional pressure variation dP5/dt∼1–7%/ms) and near-constant-volume operation (with dP5/dt∼0%/ms). The near-constant-volume ignition delay times provide a database for low-temperature propane model development that is independent of non-ideal fluid flow and heat transfer effects. Comparisons of these near-constant-volume measurements with predictions using the JetSurF v1.0 mechanism of Sirjean et al. [10] and the Curran et al. mechanism of NUI Galway [5] were performed. Ignition delay times measured with dP5/dt∼1–7%/ms were found to be significantly shorter (about 1/3 of the near-constant-volume values) at the lowest temperatures and highest pressures studied. However, these ignition times are successfully simulated using the JetSurF v1.0 mechanism when an appropriate gasdynamic model that accounts for changes in pressure and temperature is used.

Reshocks, rarefactions, and the generalized Layzer model for hydrodynamic instabilities

We report numerical simulations and analytic modeling of shock tube experiments on Rayleigh–Taylor and Richtmyer–Meshkov instabilities. We examine single interfaces of the type A/B where the incident shock is initiated in A and the transmitted shock proceeds into B. Examples are He/air and air/He. In addition, we study finite-thickness or double-interface A/B/A configurations such as air/SF6/air gas-curtain experiments. We first consider conventional shock tubes that have a “fixed” boundary: A solid endwall which reflects the transmitted shock and reshocks the interface(s). Then we focus on new experiments with a “free” boundary—a membrane disrupted mechanically or by the transmitted shock, sending back a rarefaction toward the interface(s). Complex acceleration histories are achieved, relevant for inertial confinement fusion implosions. We compare our simulation results with a generalized Layzer model for two fluids with time-dependent densities and derive a new freeze-out condition whereby accelerating and compressive forces cancel each other out. Except for the recently reported failures of the Layzer model, the generalized Layzer model and hydrocode simulations for reshocks and rarefactions agree well with each other and remain to be verified experimentally.

Application of an aerosol shock tube to the measurement of diesel ignition delay times

Shock tube ignition delay times were measured for DF-2 diesel/21% O2/argon mixtures at pressures from 2.3 to 8.0atm, equivalence ratios from 0.3 to 1.35, and temperatures from 900 to 1300K using a new experimental flow facility, an aerosol shock tube. The aerosol shock tube combines conventional shock tube methodology with aerosol loading of fuel-oxidizer mixtures. Significant efforts have been made to ensure that the aerosol mixtures were spatially uniform, that the incident shock wave was well-behaved, and that the post-shock conditions and mixture fractions were accurately determined. The nebulizer-generated, narrow, micron-sized aerosol size distribution permitted rapid evaporation of the fuel mixture and enabled separation of the diesel fuel evaporation and diffusion processes that occurred behind the incident shock wave from the chemical ignition processes that occurred behind the higher temperature and pressure reflected shock wave. This rapid evaporation technique enables the study of a wide range of low-vapor-pressure practical fuels and fuel surrogates without the complication of fuel cracking that can occur with heated experimental facilities. These diesel ignition delay measurements extend the temperature and pressure range of earlier flow reactor studies, provide evidence for NTC behavior in diesel fuel ignition delay times at lower temperatures, and provide an accurate data base for the development and comparison of kinetic mechanisms for diesel fuel and surrogate mixtures. Representative comparisons with several single-component diesel surrogate models are also given.

A diaphragmless shock tube for high temperature kinetic studies

A novel, diaphragmless shock tube (DFST) has been developed for use in high temperature chemical kinetic studies. The design of the apparatus is presented along with performance data that demonstrate the range and reproducibility of reaction conditions that can be generated. The ability to obtain data in the fall off region, confined to much narrower pressure ranges than can be obtained with a conventional shock tube is shown, and results from laser schlieren densitometry experiments on the unimolecular dissociation of phenyl iodide (P(2)=57+/-9 and 122+/-7 torr, T(2)=1250-1804 K) are presented. These are compared with results similar to those that would be obtained from a classical shock tube and the implications for extrapolation by theoretical methods are discussed. Finally, the use of the DFST with an online mass spectrometer to create reproducible experiments that can be signal averaged to improve signal/noise and the quality of mass peaks is demonstrated; something that is not possible with a conventional shock tube where each experiment has to be considered unique.

A Model of Piston Sliding Process for a Double Piston-Actuated Shock Tube

A double piston-actuated structure designed for replacing the use of diaphragms in conventional shock tubes has been recently developed. In order to clarify the piston sliding process for this structure, a simplified model based on the motion equation of its main sliding piston has been developed. Calculated piston sliding time against pressure ratio has been numerically obtained and indirectly evaluated by examining the experimental curves of the performance of the diaphragmless structure.

An experimental and theoretical high temperature kinetic study of the thermal unimolecular dissociation of fluoroethane

The thermal dissociation of fluoroethane has been studied using shock tube (ST)/time-of-flight mass spectrometry (TOF-MS) at 500 and 1200 Torr over the temperature range 1200-1550 K. The ST/TOF-MS experiments confirm that elimination of HF is the only reaction channel and rate coefficients for this reaction were extracted from concentration/time profiles derived from the mass spectra. Results from a novel diaphragmless shock tube coupled to the TOF-MS are also presented and demonstrate the unique ability of this apparatus to generate sufficiently reproducible shock waves that signal averaging can be performed over multiple experiments; something that is not possible with a conventional shock tube. The dissociation is also studied with ab initio transition state theory based master equation simulations. A modest increase in the calculated barrier height (i.e., by 1 kcal mol(-1)) yields predicted high pressure rate coefficients that are in good agreement with the existing literature data. The present pressure dependent observations are accurately reproduced for a downwards energy transfer for neon at 1200 to 1500 K of approximately 270 cm(-1), which is somewhat smaller than that found in previous studies on fluorinated ethanes with the same bath gases.

A Newly Developed Large Diameter Diaphragmless Shock Tube for Studies on CO2-N2 Gas-Dynamic Laser

A large diameter diaphragmless shock tube has been recently developed and designed to perform detailed studies of CO2-N2 gas-dynamic laser (GDL). This large diameter diaphragmless shock tube offers various advantages over the conventional shock tubes (diaphragm-type) as longer test times, higher degree of reproducibility of shock-tube data, and especially low-impurity operation condition. The latter advantage is experimentally demonstrated herein, which is very critical issue in the CO2-N2 GDL studies. A supersonic nozzle section was mounted at the end wall of the shock tube and instrumented for simultaneous measurement of laser output power and energy. The GDL action in a CO2-N2 mixture under low impurity condition has been obtained by using the large diameter diaphragmless shock tube for the first time.

Effect of exit geometry of tail pipe on the performance of pulse jet engines

In this paper, the effect of geometries of tube open end on the shock, compression and expansion waves propagating in the tube was investigated numerically and experimentally. One of them is a conventional straight shock tube with an open end. The other has a divergent tail tube at the exit. Applying a divergent tail tube (flare tube) to an open end shock tube, the period of one-cycle process could be shortened and the pressure behind the expansion wave produced at the exit of the shock tube could be lowered much more below the atmospheric pressure than that produced in the straight tube. The results suggested that the intake air into the engine was significantly increased by applying a flare tube instead of a straight tube.

The physical nature of weak shock wave reflection

For weak shock waves and small wedge angles the application of three-shock (von Neumann) theory gives no physically realistic solutions and yet experiments clearly show a pattern of reflection of three shocks meeting at a triple point. This disagreement is referred to as the von Neumann paradox, and the reflection pattern as von Neumann reflection (vNR). Some recent numerical computations have indicated the existence of an expansion wave immediately behind the reflected wave as originally suggested by Guderley over fifty years ago. Furthermore, a recent solution of the inviscid transonic equations has indicated the possible existence of a very small, multi-wave structure immediately behind the three-shock confluence. A special shock tube has been constructed which allows Mach stem lengths to be obtained which are more than an order of magnitude larger than those obtainable in conventional shock tubes. Schlieren photographs do indeed show a structure consisting of an expansion wave followed by a small shock situated behind the confluence point, with some indication of smaller scale structures in some tests. This indicates that some of the earlier models of vNR, in the parameter space tested, are incorrect. The size of the region influenced by this small wave system is about 2% of the Mach stem length and it is therefore not surprising that it has not been detected before in conventional shock tube facilities.

Experimental Investigation of Dynamic Properties of Aluminum Foams

One of the main research goals of the Protective Technologies Research and Development Center at Ben Gurion University of the Negev is to develop reliable numerical codes capable of accurately simulating the behavior of structures protected with aluminum foams exposed to explosion-generated blast-wave loads. To achieve this objective, the mechanical properties of aluminum foams under dynamic loads must be known. Several types of experimental investigations were carried out to obtain the mechanical properties of aluminum foams at different strain rates. The tests were conducted using different types of loads: static tests using an Instron compressing machine, dynamic tests using an Instron compressing machine, impact tests using a 400-kg impact pendulum, and shock-wave impact tests using conventional shock tubes. Plots of the volumetric strain as a function of the pressure and the strain rate were obtained, and the numerical codes were calibrated and validated with the aid of the experimental results.

Non-self-similar characteristics of weak Mach reflection: the von Neumann paradox

This paper deals with the von Neumann paradox, an as yet unsolved major problem in supersonic gas dynamics. We conduct a series of experiments using a conventional shock tube and focus attention on the flow-field around the triple point at various locations of the incident shock wave. By measuring the position of the triple point and the angle made by the incident and reflected shocks for propagating shock waves, we prove that the flow-field around the triple point is not self-similar. The von Neumann paradox is at least partly ascribed to non-self-similarity because classical theory assumes pseudo-steadiness that results from self-similarity for shock reflection over a wedge in a shock tube. The non-self-similarity revealed here clarifies the classical experiments by Smith (Photographic investigation of the reflection of plane Shocks in air. OSRD Report 6271, Washington, USA, 1945) and Bleakney and Taub (Rev. Mod. Phys. 21 (1949) 584). Specifically, since they implicitly assumed self-similarity, they only measured the wave angles at some particular location for each reflecting wedge angle, and their relations between angles of incidence and reflection were recovered by the present experiment.

Stark widths of faint Si II lines

Line profiles of faint Si  lines of astrophysical interest are observed in a conventional shock tube. Electron density is 1.3 × 10 23 m −3 , and the temperature is 11 000 K. The Stark effect is the dominant broadening mechanism. The Si  line at λ 419.07 nm (multiplet 7.26, Moore 1965) Stark width is measured and compared with theoretical prediction.

Absorption spectroscopy of toluene pyrolysis

Toluene pyrolysis in high temperature/high pressure argon atmosphere has been studied in a conventional diaphragm-type shock tube. The investigated ranges of temperature and pressure were 1500–2300 K and 8–13 bar, respectively. Extinction measurements in the near infrared have been carried out to follow the formation of carbonaceous particulate (soot). Pyrolysis products were optically characterized by absorption measurements in the wavelength range 300–800 nm, with high time/spectral resolution. The application of Tauc analysis to the absorption spectra allowed to identify three levels of energy gap; they have been attributed to carbonaceous structures with 3–5 and 7–9 fused aromatic rings, and to soot particles.

Study on Performance of Detonation-Driven Shock Tube

A detonation-driven shock tube firstly designed by H.R. Yu is considered to be a useful apparatus for producing high-enthalpy flow. In this apparatus, a strong shock wave is generated by detonating an oxygen-hydrogen mixture (oxy-hydrogen) and the driver gas temperature and pressure are extremely high compared with those of a conventional shock tube. However, the structure of the detonation wave is not uniform, e.g., the detonation wave has three-dimensional cellular structures and multiple transverse waves. Furthermore, the detonation wave is followed by a Taylor expansion fan and the performance of detonation-driven shock tube is not well understood. In this preliminary study, a detonation-driven shock tube is constructed and its performance is experimentally investigated by measuring pressure histories and the profile of the ionization current behind the detonation wave