Open-ended Shock Tube Research Articles

A Study on the interaction of shock tube-generated blast waves with a circular object at different pressure ratios

The interaction of high peak overpressure blast waves with a circular object placed at two different axial locations from the shock tube exit is studied through numerical simulation using an in-house developed multi-component Navier–Stokes solver. The driver and driven sections of the shock tube were 0.8 m and 6 m, respectively. Helium is used in the driver section, while atmospheric air is used in the driven section and outside the shock tube. The evolution of blast waves inside an open-ended shock tube and its interaction with a rectangular object is reported in Murugan et al.. (2022). Here, the blast wave interacting with a circular object is examined for diaphragm pressure ratios of 13 and 57 by placing the objects at 250 mm and 500 mm from the shock tube exit. The flow field is evaluated through numerical Schlieren, vorticity, density, pressure plots, and the enstrophy plot, which shows the vortical structures that originated in the flow field. The blast load acting on the circular object is calculated for two diaphragm pressure ratios and axial locations. This study helps understand the reflection and diffraction of blast waves and associated flow fields around circular objects used in blast wave attenuation.

Effect of driver gas composition on production of scaled Friedlander waveforms in an open-ended shock tube model

With the evolution of modern warfare and the increased use of improvised explosive devices (IEDs), there has been an increase in blast-induced traumatic brain injuries (bTBI) among military personnel and civilians. The increased prevalence of bTBI necessitates bTBI models that result in a properly scaled injury for the model organism being used. The primary laboratory model for bTBI is the shock tube, wherein a compressed gas ruptures a thin membrane, generating a shockwave. To generate a shock wave that is properly scaled from human to rodent subjects many pre-clinical models strive for a short duration and high peak overpressure while fitting a Friedlander waveform, the ideal representation of a blast wave. A large variety of factors have been experimentally characterized in attempts to create an ideal waveform, however we found current research on the gas composition being used to drive shock wave formation to be lacking. To better understand the effect the driver gas has on the waveform being produced, we utilized a previously established murine shock tube bTBI model in conjunction with several distinct driver gasses. In agreement with previous findings, helium produced a shock wave most closely fitting the Friedlander waveform in contrast to the plateau-like waveforms produced by some other gases. The peak static pressure at the exit of the shock tube and total pressure 5 cm from the exit have a strong negative correlation with the density of the gas being used: helium the least dense gas used produces the highest peak overpressure. Density of the driver gas also exerts a strong positive effect on the duration of the shock wave, with helium producing the shortest duration wave. Due to its ability to produce a Friedlander waveform and produce a waveform following proper injury scaling guidelines, helium is an ideal gas for use in shock tube models for bTBI.

Aerodynamic fragmentation of water, ethanol and polyethylene glycol droplets investigated by high-speed in-line digital holography

Digital holography is a remarkable interferometric technique for determining the size, shape, distribution, and spatial location of particles. Therefore, when combined with high-speed imaging technology, it represents a relevant technique for the study of the aerodynamic fragmentation phenomenon wherein the aerodynamic strengths counterbalance the cohesion forces of the drops causing thus their decomposition. We discuss in this paper the droplets fragmentation of water, ethanol and polyethylene glycol 300 solutions interacting with a shock wave and flow generated by an open-ended shock tube. In this context, a shock tube device was set up, and both the released flow as well as the shock wave generated were characterized by ultrafast imaging shadowgraphy and high speed pressure measurement. Millimeter diameter average drops are fragmented and imaged by high-speed digital in-line holography at a rate of 24800 fps, and then the image retrieved numerically. The Weber numbers are determined for each liquid and the observed fragmentation patterns are consistent with the description of the ‘chaotic regime’ reported in the literature by Pilch and Erdman (1987) [1].

Structural disruption of the blood\u2013brain barrier in repetitive primary blast injury

BackgroundBlast-induced traumatic brain injury (bTBI) is a growing health concern due to the increased use of low-cost improvised explosive devices in modern warfare. Mild blast exposures are common amongst military personnel; however, these women and men typically do not have adequate recovery time from their injuries due to the transient nature of behavioral symptoms. bTBI has been linked to heterogeneous neuropathology, including brain edema, neuronal degeneration and cognitive abnormalities depending on the intensity of blast overpressure and frequency. Recent studies have reported heterogeneity in blood–brain barrier (BBB) permeability following blast injury. There still remains a limited understanding of the pathologic changes in the BBB following primary blast injuries. In this study, our goal was to elucidate the pathologic pattern of BBB damage through structural analysis following single and repetitive blast injury using a clinically relevant rat model of bTBI.MethodsA validated, open-ended shock tube model was used to deliver single or repetitive primary blast waves. The pathology of the BBB was assessed using immunofluorescence and immunohistochemistry assays. All data were analyzed using the one-way ANOVA test.ResultsWe have demonstrated that exposure to repetitive blast injury affects the desmin-positive and CD13-positive subpopulations of pericytes in the BBB. Changes in astrocytes and microglia were also detected.ConclusionThis study provides analysis of the BBB components after repetitive blast injury. These results will be critical as preventative and therapeutic strategies are established for veterans recovering from blast-induced traumatic brain injury.

Experimental Analysis of Acoustic Performance of Porous Ducts using a Small- scale Shock tube

A Shock tube is a device often used to recreate the shock phenomena by several methods. The present work is a preliminary study to analyse the efficiency of baffles in suppressing the noise generated from the shock associated jet ejected from the duct exit. The experiment was performed at a shock Mach number of 1.27 using a diaphragm based, small scale, open ended shock tube. Parametric study conducted by varying the baffle dimensions such as outer diameter, hole diameter and porosity reveals that the baffles with hole diameter less than half of the baffle diameter and with a greater porosity is a cost effective and efficient noise suppressor for shock associated jets.

Characterization of a novel open-ended shock tube facility based on detonation transmission tubing

Abstract This paper proposes and demonstrates a novel shock tube driven by commercially available detonation transmission tubing in a safe, repeatable, and controllable manner for laboratory scale experiments. A circular cross-sectional open-ended shock tube (inner-diameter D = 22 mm ) driven by detonation transmission tubing was used to investigate the working principle of this novel shock tube using a dynamic pressure transducer and time-resolved shadowgraph photography. Specifically, the shock Mach number, repeatability, and flow structure generated from the tube exit were characterized. The experimental result shows that the flow structure including an initial shock wave, a vortex ring, an embedded shock, and an oblique shock pattern is similar to that of the conventional compressed-gas driven shock tubes. Furthermore, the shock tube has good repeatability of less than 2% with a shock Mach number up to 1.58. The versatile and cost-effective nature of the shock tube driven by detonation transmission tubing opens a new horizon for shock wave-assisted interdisciplinary applications.

Time-resolved quantitative visualization of complex flow field emitted from an open ended shock tube using a wavefront measuring camera

Quantitative visualization of shock-induced complex flow field emanating from the open end of a miniaturized hand-driven shock tube (Reddy tube) is presented. During operation, the planar shock wave of Mach number Mi=1.33 (±0.6%) is discharged through the low-pressure driven-section, kept open to ambient room condition. From the moment of shock discharge, its after effects of evolving flow field are recorded for 300 μsnear the exit of the tube by using a high resolution (16 MP) wavefront measuring camera (WC) setup. The ability of the camera to identify the amplitude and phase of the incident light wave is utilized to measure the flow induced change in phase of the interrogating light beam quantitatively. Information about the evolving flow field with a spatial resolution of 40 μm/pixel (for a field of view (FOV) 120 mm × 120 mm) and time resolution of 50 μsis recorded in repeated runs. The measured phase information is used in the iterative refraction tomographic scheme to recover the three-dimensional (3D) density distribution of the flow field quantitatively, which reveals the internal features of the domain. Computational fluid dynamic (CFD) simulation is carried out for the same experimental conditions and it is found that recovered experimental density distribution shows good agreement with the results obtained through CFD simulation.

A Novel In Vitro Model of Blast Traumatic Brain Injury.

Traumatic brain injury is a leading cause of death and disability in military and civilian populations. Blast traumatic brain injury results from the detonation of explosive devices, however, the mechanisms that underlie the brain damage resulting from blast overpressure exposure are not entirely understood and are believed to be unique to this type of brain injury. Preclinical models are crucial tools that contribute to better understand blast-induced brain injury. A novel in vitro blast TBI model was developed using an open-ended shock tube to simulate real-life open-field blast waves modelled by the Friedlander waveform. C57BL/6N mouse organotypic hippocampal slice cultures were exposed to single shock waves and the development of injury was characterized up to 72 h using propidium iodide, a well-established fluorescent marker of cell damage that only penetrates cells with compromised cellular membranes. Propidium iodide fluorescence was significantly higher in the slices exposed to a blast wave when compared with sham slices throughout the duration of the protocol. The brain tissue injury is very reproducible and proportional to the peak overpressure of the shock wave applied.

Numerical Visualization of Blast Wave Interacting with Objects

Blast wave interaction with objects has gained attention due to military conflict and terrorist attack across the globe. Blast wave attenuating and mitigating structures are needed to be developed to protect the military vehicles and commercial buildings. In order to understand the attenuating mechanism such as the dissipation and dispersion along with the secondary effects, the blast wave interacting with three objects is examined in the present study for the diaphragm pressure ratio of 56. Here, the blast wave is generated in a short driver section open ended shock tube by solving the Euler equations using the commercial software ANSYS Fluent. It has been observed that the circular disc attenuates the blast wave more effectively compared to the cone and sphere for the same frontal area. The attenuation was lowest in the sphere and maximum in the circular disc. However, the loads acting on the sphere was more compared to the conical object. The peak load acting on the circular disc was 2.09 times more compared to the peak load acting on the conical object (cone angle 26.5°) with the same hydraulic diameter.

A moving boundary flux stabilization method for Cartesian cut-cell grids using directional operator splitting

An explicit moving boundary method for the numerical solution of time-dependent hyperbolic conservation laws on grids produced by the intersection of complex geometries with a regular Cartesian grid is presented. As it employs directional operator splitting, implementation of the scheme is rather straightforward. Extending the method for static walls from Klein et al. (2009) [37], the scheme calculates fluxes needed for a conservative update of the near-wall cut-cells as linear combinations of “standard fluxes” from a one-dimensional extended stencil. Here the standard fluxes are those obtained without regard to the small sub-cell problem, and the linear combination weights involve detailed information regarding the cut-cell geometry. This linear combination of standard fluxes stabilizes the updates such that the time-step yielding marginal stability for arbitrarily small cut-cells is of the same order as that for regular cells. Moreover, it renders the approach compatible with a wide range of existing numerical flux-approximation methods. The scheme is extended here to time dependent rigid boundaries by reformulating the linear combination weights of the stabilizing flux stencil to account for the time dependence of cut-cell volume and interface area fractions. The two-dimensional tests discussed include advection in a channel oriented at an oblique angle to the Cartesian computational mesh, cylinders with circular and triangular cross-section passing through a stationary shock wave, a piston moving through an open-ended shock tube, and the flow around an oscillating NACA 0012 aerofoil profile.

Experimental and Numerical Investigation of Blast Wave Interaction With a Three Level Building

The present work shows that weak blast waves that are considered as being harmless can turn to become fatal upon their reflections from walls and corners inside a building. In the experimental part, weak blast waves were generated by using an open-end shock tube. A three level building model was placed in vicinity to the open-end of the used shock tube. The evolved wave pattern inside the building rooms was recorded by a sequence of schlieren photographs; also pressure histories were recorded on the rooms' walls. In addition, numerical simulations of the evolved flow field inside the building were conducted. The good agreement obtained between numerical and experimental results shows the potential of the used code for identifying safe and dangerous places inside the building rooms penetrated by the weak blast wave.

Consequences of liquid jet breakup resulting from interaction with overpressure wave from domino effect

Storage tanks located on industrial sites are potential source term for leakages, followed by various consequences depending on the nature of the commodity: atmospheric dispersion, BLEVE, UVCE, toxic dispersion. Indeed, because of economic and security purposes, chemical substances are stored with different conditions of pressure, temperature and state. This study explores the consequences of a sudden opening of a storage tank due to an external aggression as a consequence from a previous event. Fragmentation of jets and droplets following the trigger event are thus evaluated. Indeed, increasing the exchange surface impacts the evaporation rate and can be an issue in case of toxic or flammable vapor. Laboratory experiments consisted in generating shockwave with an open ended shock tube to breakup liquid droplets with different viscosities. Size of fragmented droplets are optically measured by direct shadowgraphy. Shockwave is measured using both overpressure sensors and Edgerton retroreflective shadowgraphy. In these experiments, secondary breakups of a droplet into an important number of smaller droplets because of the shockwave induced flow are performed. Results are discussed in terms of velocity and size of droplets. Comparisons are made with existing fragmentation models such as Pilch and Erdman (1987) to provide up to date data with situations encountered in industrial risk evaluation.

High-speed imaging optical techniques for shockwave and droplets atomization analysis

Droplets atomization by shockwave can act as a consequence in domino effects on an industrial facility: aggression of a storage tank (projectile from previous event, for example) can cause leakage of hazardous material (toxic and flammable). As the accident goes on, a secondary event can cause blast generation, impacting the droplets and resulting in their atomization. Therefore, exchange surface increase impacts the evaporation rate. This can be an issue in case of dispersion of such a cloud. The experiments conducted in the lab generate a shockwave with an open-ended shock tube to break up liquid droplets. As the expected shockwave speed is about 400 m/s (∼Mach 1.2), the interaction with falling drops is very short. High-speed imaging is performed at about 20,000 fps. The shockwave is measured using both overpressure sensors: particle image velocimetry and pure in line shadowgraphy. The size of fragmented droplets is optically measured by direct shadowgraphy simultaneously in different directions. In these experiments, secondary breakups of a droplet into an important number of smaller droplets from the shockwave-induced flow are shown. The results of the optical characterizations are discussed in terms of shape, velocity, and size.

Structural and biochemical abnormalities in the absence of acute deficits in mild primary blast-induced head trauma.

Blast-induced neurotrauma (BINT), if not fatal, is nonetheless potentially crippling. It can produce a wide array of acute symptoms in moderate-to-severe exposures, but mild BINT (mBINT) is characterized by the distinct absence of acute clinical abnormalities. The lack of observable indications for mBINT is particularly alarming, as these injuries have been linked to severe long-term psychiatric and degenerative neurological dysfunction. Although the long-term sequelae of BINT are extensively documented, the underlying mechanisms of injury remain poorly understood, impeding the development of diagnostic and treatment strategies. The primary goal of this research was to recapitulate primary mBINT in rodents in order to facilitate well-controlled, long-term investigations of blast-induced pathological neurological sequelae and identify potential mechanisms by which ongoing damage may occur postinjury. A validated, open-ended shock tube model was used to deliver blast overpressure (150 kPa) to anesthetized rats with body shielding and head fixation, simulating the protective effects of military-grade body armor and isolating a shock wave injury from confounding systemic injury responses, head acceleration, and other elements of explosive events. Evans Blue-labeled albumin was used to visualize blood-brain barrier (BBB) compromise at 4 hours postinjury. Iba1 staining was used to visualize activated microglia and infiltrating macrophages in areas of peak BBB compromise. Acrolein, a potent posttraumatic neurotoxin, was quantified in brain tissue by immunoblotting and in urine through liquid chromatography with tandem mass spectrometry at 1, 2, 3, and 5 days postinjury. Locomotor behavior, motor performance, and short-term memory were assessed with open field, rotarod, and novel object recognition (NOR) paradigms at 24 and 48 hours after the blast. Average speed, maximum speed, and distance traveled in an open-field exploration paradigm did not show significant differences in performance between sham-injured and mBINT rats. Likewise, rats with mBINT did not exhibit deficits in maximum revolutions per minute or total run time in a rotarod paradigm. Short-term memory was also unaffected by mBINT in an NOR paradigm. Despite lacking observable motor or cognitive deficits in the acute term, blast-injured rats displayed brain acrolein levels that were significantly elevated for at least 5 days, and acrolein's glutathione-reduced metabolite, 3-HPMA, was present in urine for 2 days after injury. Additionally, mBINT brain tissue demonstrated BBB damage 4 hours postinjury and colocalized neuroinflammatory changes 24 hours postinjury. This model highlights mBINT's potential for underlying detrimental physical and biochemical alterations despite the lack of apparent acute symptoms and, by recapitulating the human condition, represents an avenue for further examining the pathophysiology of mBINT. The sustained upregulation of acrolein for days after injury suggests that acrolein may be an upstream player potentiating ongoing postinjury damage and neuroinflammation. Ultimately, continued research with this model may lead to diagnostic and treatment mechanisms capable of preventing or reducing the severity of long-term neurological dysfunction following mBINT.

A Model of Low-Level Primary Blast Brain Trauma Results in Cytoskeletal Proteolysis and Chronic Functional Impairment in the Absence of Lung Barotrauma

Shock-wave exposure from improvised explosive devices (IEDs) has been implicated as a possible contributing factor to neurological impairment reported in combat veterans. However, evidence-based substantiation of this implication, particularly for low-level exposure in the absence of external signs of trauma, remain elusive. Accordingly, we constructed an open-ended shock tube producing a short-duration, low-amplitude shockwave. Low-level (11.5 kPa static overpressure) complex shock-wave exposure in rats resulted in no histological evidence of lung injury. By contrast, delayed cytoskeletal proteolysis of αII-spectrin was detected in the cortex and hippocampus by 12 h post-injury. Cell death was minimal and localized predominantly in the corpus callosum and periventricular regions. These regions, with presumably different density interfaces, exhibit biological responses to shockwaves consistent with interface turbulence described by Richtmyer-Meshkov instability. Evoked compound action potential (CAP) recordings from the corpus callosum showed a significant increase in the duration of CAP responses at 14 and 30 days post-injury, and a gradual depression in the unmyelinated fiber amplitude. Shielding the head attenuated αII-spectrin cytoskeletal breakdown, thus directly implicating low-level shock-wave exposure as a cause of brain injury in the rat. Despite anatomical and scaling differences in rats compared to humans, the results suggest the potential for undiagnosed traumatic brain pathologies occurring in combat veterans following shock-wave exposure.

Exhaust of Underexpanded Jets from Finite Reservoirs

We examine the response of an underexpanded jet to a depleting, nite reservoir with experiments and simulations. An open-ended shock tube facility with variable reservoir length is used to obtain images of nitrogen and helium jet structures at successive instances during the blowdown from initial pressure ratios of up to 250. The reservoir and ambient pressures are simultaneously measured to obtain the instantaneous pressure ratio. We estimate the time-scales for jet formation and reservoir depletion as a function of the specic heat ratio of the gas and the initial pressure ratio. The jet structure formation time-scale is found to become approximately independent of pressure ratio for ratios greater than 50. In the present work, no evidence of time-dependence in the Mach disk shock location is observed for rates of pressure decrease associated with isentropic blowdown of a nite reservoir while the pressure ratio is greater than 15. The shock location in the nitereservoir jet can be calculated from an existing empirical t to innite-reserv oir jet data evaluated at the instantaneous reservoir pressure. For pressure ratios below 15, however, the present data deviate from a compilation of data for innite-reserv oir jets. A new t is obtained to data in the lower pressure regime. The self-similarity of the jet structure is quantied and departure from similarity is noted to begin at pressure ratios lower than about 15, approximately the same ratio which limits existing empirical ts.

Time-resolved visualization of shock–vortex systems emitted from an open shock tube

When a shock wave leaves an open-ended shock tube, it generates a vortex ring that subsequently detaches from the shock tube and follows the expanding shock front. This classical problem of shock–vortex interaction has been visualized in unprecedented detail and temporal resolution by means of time-resolved shadow, schlieren and shearing interferometry sequences obtained with a newly developed ultrahigh-speed color video camera. This device is capable of taking 144 frames with full-frame resolution of 720 × 410 pixels at rates of up to one million frames per second. Apart from shadowgraphy, the visualization techniques used in this study were direction- and magnitude-indicating color schlieren and polychrome shearing interferometry. The process was observed both with the standard normal view of the flow field and with an oblique view, which facilitated the identification of some three-dimensional flow features. The obtained results clearly show the development of individual flow elements, including some that so far have eluded a proper description. One example is the secondary, counter-rotating vortex ring, which at a later time wraps around the main vortex ring before disintegrating upon merging with the shear layer that surrounds the gas exiting from the tube.

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.

Symmetry breaking, ring formation and other phase boundary structures in shock tube experiments on retrograde fluids

A peculiar multi-dimensional wave pattern in shock tube experiments on retrograde fluids is the ring formation phenomenon. When the incident shock is reflected by the endwall of a shock tube filled with retrograde fluid vapour, under certain conditions, rings of liquid/vapour mixture form behind the reflected shock. In this paper, we find the reason for such symmetry breaking and ring formation phenomena by studying a prototype model for flows with liquid/vapour phase transitions. The isothermal case of this model exhibits all major one-dimensional wave patterns observed in shock tube experiments on retrograde fluids. The symmetry is broken by the liquid or liquid/vapour drops initiated behind the reflected shock where the pressure is higher than the equilibrium pressure. Liquid drops become liquid/vapour mixture drops later. Using a liquid/vapour mixture drop at the reflecting wall as the initial condition for the prototype model, it is shown that this drop will evolve into a ring, yielding the explanation for ring formation. The outer fronts of rings are collapsing waves. Such waves are supersonic, as confirmed by some photographs of actual experiments. It is also shown that a liquid or liquid/vapour mixture drop cannot evolve into a ring if no reflecting wall is present, agreeing with experimental observation. A mechanism is also provided by the model for the emergence of the ‘button’ at the centre of, and the small-scale asperities at, the liquefaction shock front observed at the exit of the open-end shock tube.

Discharge of a shock wave from an open end of a tube

When a pressure wave propagates along a constant area straight tube and reaches at the open end, an impulsive wave is emitted outward from the tube exit toward the surrounding area and causes an impulsive noise like a sonic boom. In order to clarify the magnitude of an impulsive wave obtained by the discharge of a weak shock wave from an open end of a tube in relation to the noise problem and the industrial devices, the experimental and numerical investigations have been carried out for various strength of a shock wave. A simple open end shock tube with the flange at the tube exit was used and the numerical calculation using the TVD scheme was performed. The effective equations which concerns with the magnitude of an impulsive wave generated by the emission of a shock wave have been obtained from the procedure of the open end correction based on the aeroacoustic theory and the numerical results. The influence of open end correction length and the diameter of a flange on the magnitude of an impulsive wave has been discussed.