Driven Shock Tube Research Articles

Characterization of a large caliber explosively driven shock tube.

Research on evaluating weapon systems, building structures, and personnel protection has attracted considerable attention due to the high incidence of blast accidents. The explosively driven shock tube is an affordable and replicable method for investigating high pressure blast waves and extreme shock environments. A newly constructed large caliber explosively driven shock tube with an inner diameter of 2.5m and a length of 18m has been documented and characterized in this paper. It is capable of providing a peak pressure of at least 5.49 MPa in the test section with 160kg of TNT charges. The tube can produce an overpressure that is significantly higher than conventional shock tubes, which expands the capability to simulate a high overpressure blast load. A two-dimensional axisymmetric simulation model has been developed, validated, and calibrated for the characterization of the flow field inside the shock tube. The influence of the charge mass on the overpressure, arrival time, and positive impulse was discussed, and the planarity of the shock wave was also quantitatively characterized. To aid in designing further shock experiments and applications, a physics-based prediction model was developed using the dimensional analysis.

A simple, self-sufficient approach for the design of shock tube driver insert

A simple, self-sufficient approach for the design of shock tube driver insert

Experimental investigation of non-equilibrium spectra for nitrogen behind strong shock waves

The non-equilibrium spectra of shock-heated nitrogen in the UV-visible range are investigated in a detonation driven shock tube. Spectral identification indicates that the main contributors to the spectra are molecular radiation of N2(2+) and N2+(1-). Vibrational and rotational temperatures of N2(C) and N2+(B) are determined through spectral fitting. The post-shock spectra of pure nitrogen are obtained for shock velocities ranging from 6.82–9.00 km/s and P0 = 30–200 Pa at the shock arrival time. Differences between vibrational and rotational temperatures of N2(C) and N2+(B) are observed, suggesting that nitrogen is in a non-equilibrium state at shock arrival moment. Time-resolved spectra are obtained within varying delay times of 0–2.0μs at P0 = 200 Pa and shock velocity of Vsw = 6.60 km/s. Time-resolved temperatures are determined to illustrate the time-resolved non-equilibrium characteristics of nitrogen at high temperature. It is observed that the non-equilibrium characteristics of nitrogen gradually weaken with increasing time and the thermal equilibrium was not obtained within 2.0μs. Finally, the time-resolved temperatures are compared with CEA (Chemical Equilibrium with Applications) prediction, revealing that the difference in temperature between the experiment and the CEA equilibrium calculation decreases as time increases.

Radiation properties of air behind strong shock wave

The problem of descent spacecrafts safety is closely related to the correct assessment of heat fluxes to their surface. This work is devoted to an experimental study of radiative heat fluxes that play an important role during the entry of a spacecraft into the Earth's atmosphere at superorbital velocity.The radiation properties of high-temperature air were measured in the detonation driven shock tube DDST-M at the gas pressure 0.25 Torr ahead of the shock wave in the shock wave velocity range from 7.7 to 11.4 km/s. The applied registration method fixates the time-integrated distribution of the radiation intensity of the shock heated air passing by the measuring cross section. The measurements were carried out in the spectral range from 190 to 1100 nm. Simultaneously, the evolution of the radiation power at certain wavelengths that are selected using monochromators was recorded. Time spectrograms at certain wave lengths make it possible to determine the effective process time that can be used to recalculate the measured integral radiation intensity to the radiation power that traditionally measures by 3-D spectroscopy method. A new spectral model is presented that performs a line-by-line calculation of the emission and absorption spectra of atoms and molecules. The experimental results are compared with the calculated data obtained using the spectral model, as well as data from other measurements.

A transient heat flux sensor for PbTe thin films based on transverse Seebeck effect

Among thermoelectric materials with thermoelectric effect, lead telluride (PbTe) is widely used because of its high performance and chemical stability in the medium temperature region. In this study, PbTe was creatively employed to develop a transient thin films heat flux sensor (THFS) using magnetron sputtering technique based on the transverse Seebeck effect. After static and dynamic calibration, the rise time of the THFS is 35 μs and the sensitivity is up to 7.9 μV(kW·m−2)−1, it can be measured in transient high heat flux testing environments without the need for a signal amplifier. In the experiment of measuring transient heat flux with explosion driven shock tube, the THFS has the advantages of high resolution and high dynamic response, which provides scientific basis for the study of explosion thermal damage effect and has important significance.

Steady rotation of a Mach shock: experimental and numerical evidences

This experimental and numerical work reports on the dynamical behaviour of a shock in an inert gas at the concave wall of a hollow circular chamber. The gas in the chamber was air or He + $${\rm O}_{2}$$ + 2 Ar at initial pressures $$p_{{\rm c0}}$$ ranging from 2 to 12 kPa and initial temperature T0 =288 K. The shock was generated using a detonation driven shock tube. The shock dynamics were characterized through high-speed shadowgraph recordings and high-resolution numerical simulations. For each gas and $$p_\text {c0}$$ , the experiments evidenced the formation of a Mach reflection along the wall and identified a range of initial pressures for which this configuration rotates with constant stem heights and constant velocities larger than those at the chamber entry. The numerical simulations were capable of capturing the dynamics quantitatively. These results extend to inert gases our previous work with a reactive gas for which we reported on the possibility of a steadily rotating overdriven Mach detonation. The steadiness range is narrower with the inert gases, likely because of the smaller initial pressure ratios at the chamber entry and lower support from the subsonic flow behind the shock. The initial support in the reactive case was more efficient because the discontinuities at the chamber entry were self-sustained Chapman–Jouguet detonations. Further investigations of these Mach rotating regimes should rely only on specific experiments and numerical simulations, for example, on the effect of the chamber dimensions, because of the complex non-dimensional formulation of the problem.

An experimental and numerical investigation of the effects of the diaphragm pressure ratio and its position on a heated shock tube performance

AbstractThe main purpose of this work was to investigate the performance of heated shock tube (ST) with different pressure ratios and diaphragm positions numerically and experimentally. The numerical model was developed to simulate the fluid flow inside a shock tube test facility located at Qatar University. The shock tube was a cast‐iron hollow tube with 6 m length, 50 mm internal diameter and 10 mm thickness. ST driver and driven sections were filled with helium–argon mixture and air. The driven section was heated up to 150°C using coils. At the middle of the ST, the diaphragm was made of aluminium sheet (0.5 mm) layers. Five different pressure ratios were implemented during the experiment, and performance evaluation depended on the strength of the incident shock Mach number. The inviscid numerical model solver used transient two‐dimensional time‐accurate Navier–Stokes CFD. The model introduced a parametric study regarding three different diaphragm positions (1m, 2m and 3m) and five pressure ratios (6–10) for each position. In addition to yielding the incident and reflected wave Mach number, reflected wave temperature was also considered a shock tube performance indicator. The incident Mach numbers for the diaphragm middle position from the experiment were compared against those conducted from the model, and good matching was observed. The parametric study results showed that at high‐pressure ratios, diaphragm Positions 1 and 3 could generate a 7.4% increase in shock wave Mach number compared with the diaphragm position‐2 model. Moreover, the diaphragm position‐3 model tends to have a 2% increase in the temperature behind the reflected shock wave compared with the other two positions.

Experimental study of air radiation behind a strong shock wave

This paper presents a description of the modernized detonation driven shock tube DDST-M, in which conditions that simulate the entry of spacecraft into the Earth's atmosphere at the super orbital velocity (11.2 km/s) are achieved. The modernization consists in the inclusion of an additional element in the shock tube design - the prechamber, which separates the end wall of the tube with the igniter from the main volume by the perforated disc. The presence of the prechamber increases the energy efficiency of the facility, primarily due to a more complete combustion of the combustible mixture in the high-pressure chamber, which makes it possible to obtain higher shock wave velocities in the low-pressure chamber. A series of experiments was carried out to study the radiation characteristics of high temperature air in the range of shock wave velocities VSW = 4.2 ÷ 11.4 km/s and initial gas pressures p0 = 0.25 ÷ 10 Torr. Analysis of the obtained data made it possible to distinguish the features of the radiation in different parts of the spectrum depending on the shock wave velocity and the initial gas pressure. The measurement results are compared with the results of other studies.

High-Temperature Ignition Kinetics of Gas Turbine Lubricating Oils

Abstract Lubricant ignition is a highly undesirable event in any mechanical system, and surprisingly minimal work has been conducted to investigate the auto-ignition properties of gas turbine lubricants. To this end, using a recently established spray injection scheme in a shock tube, two gas turbine lubricants (Mobil DTE 732 and Lubricant A from Cooper et al. 2021, “Auto-Ignition of Gas Turbine Lubricating Oils in a Shock Tube Using Spray Injection,” ASME J. Eng. Gas Turbines Power, 143(5), p. 051008) were subjected to high-temperature, post-reflected-shock conditions, and OH* chemiluminescence was monitored at the sidewall location of the shock tube to measure ignition delay time (τign). A combination of an extended shock-tube driver and driver-gas tailoring were utilized to observe ignition between 1183 K and 1385 K at near-atmospheric pressures. A clear, two-stage-ignition process was observed for all tests with Mobil DTE 732, and both first and second stage τign are compared. Second stage ignition was found to be more indicative of lubricant ignition and was used to compare τign values with lubricant A. Both lubricants exhibit three ignition regimes: a high-temperature, Arrhenius-like regime (>1275 K); an intermediate, negative-temperature-coefficient-like regime (1230 –1275 K); and a low-temperature ignition regime (<1230 K). Similar τign behavior in the high-temperature regime was seen for both lubricants, and a regression analysis using τign data from both lubricants in this region produced the Arrhenius expression τign(μs) = 4.4 × 10−14 exp(96.7(kcal/mol)/RT). While lubricant A was found to be less reactive in the intermediate-temperature regime, Mobil DTE 732 was less reactive in the low-temperature regime. As the low-temperature regime is more relevant to gas turbine conditions, Mobil DTE 732 is considered more desirable for system implementation. Chemical kinetic modeling was also performed using n-hexadecane models (a lubricant surrogate suggested in the literature). The current models are unable to reproduce the three regimes observed and predict activation energies much lower than those observed in the high-temperature regime, suggesting n-hexadecane is a poor surrogate for lubricant ignition. Additionally, experiments were conducted with Jet-A for temperatures between 1145 and 1419 K around 1 atm. Good agreement is seen with both literature data and model predictions, anchoring the experiment with previously established τign measurement methods and calculations. A linear regression analysis of the Jet-A data produced the Arrhenius expression: τign(μs) = 6.39 × 10−5exp(41.4(kcal/mol)/RT).

Predicting the self-centering behavior of hybrid FRP-steel reinforced concrete beams under blast loading

An inelastic single-degree-of-freedom (SDOF) dynamic analysis model is developed to predict the entire displacement time-history of concrete beams reinforced with hybrid mixtures of fiber reinforced polymer (FRP) and steel reinforcing bars subjected to blast loads. Hybrid FRP-steel reinforced concrete members exhibit strong self-centering tendencies which promote blast resilience through reductions in residual damage, repair cost, and facility downtime after a terrorist bomb attack or accidental explosion. FRP bars provide an internal restoring force that activates self-centering behavior after the inertial loads are removed, while the conventional steel reinforcement and concrete dissipate energy by their inelastic response. The SDOF model is equally applicable to all-steel, all-FRP, and hybrid FRP-steel reinforced concrete flexural members, incorporating all the relevant parameters of flexural response, nonlinearity, and self-centering that have been observed to play an important role in blast tests. These parameters include the type, size, spacing, arrangement, and material properties of longitudinal and transverse reinforcement, as well as concrete properties and section geometry. The effect of these parameters is described in terms of nonlinear resistance functions capturing the inbound and rebound flexural response, plastic hinge formulations to account for crack bridging provided by FRP bars, and a hysteretic model for the combined effects of self-centering behavior and stiffness degradation due to accumulated damage from progressively increasing repeated blast tests. A new response parameter, known as the Blast Self-Centering Index (BSI), is proposed to evaluate and assess the residual displacements of all-steel, all-FRP, and hybrid FRP-steel reinforced concrete beams predicted by SDOF analysis. The model has been verified extensively against data obtained from explosively driven shock tube blast experiments.

Effect of shock waves on enhancing the optical properties of Ammonium Pentaborate Hexahydrate single crystal molecular structure

Ammonium Pentaborate Hexahydrate (APBHH), a novel inorganic nonlinear optical single crystal was grown by slow evaporation solution growth method and the Properties of the grown crystals were investigated. The grown crystal was subjected to single crystal XRD and Powder X-ray diffraction analysis to confirm the crystal structure to the monoclinic system with centrosymmetric nature. The presence of various functional groups has been identified by using FT-IR spectral analysis ranging between 4000 and 500 cm−1. The percentage of optical absorbance was ascertained by recording the UV-Vis spectrum, crystals shows transparent in the entire visible region with a 5.56 eV optical bandgap. The dielectric constant and dielectric loss of APBHH crystal as a function of frequency and an AC resistivity, conductivity with impedance also were calculated at room temperature. Ammonium Pentaborate Hexahydrate (APBHH) crystal under pre and post shock loaded conditions. A shock wave of Mach number 1.7 was utilized for the present investigation which was generated by a table-top pressure driven shock tube. The optical properties of test material are investigated by UV-Visible spectrometer over the range between 200 and 800 nm. The observed result showed that the transparency of the crystal increase by applying Shock Waves.

Assessment of Compression Driven Shock Tube Designs in Replicating Free-Field Blast Conditions for Traumatic Brain Injury Studies.

Compression driven shock tubes are indispensable in studies of blast-induced traumatic brain injury (bTBI). The ability of shock tubes in faithfully recreating free-field blast conditions is of enormous interest and has a direct impact on injury outcomes. Toward this end, the evolution of blast wave inside and outside of the compression driven shock tube has been studied using validated, finite element based shock tube models. Several shock tube configurations (uniform cross-section, transition, conical, suddenly expanded, and end plate) have been considered. The finite element modeling approach has been used to simulate the transient, dynamic response of blast wave propagation. The response is studied for longer durations (40-100 msec) compared with the existing literature. We demonstrate that locations inside and outside of the shock tube can generate free-field blast profile in some form, but with numerous caveats. Our results indicate that the locations inside the shock tube are affected by higher underpressure and corresponding kinetic energy yield compared with free-field blast. These effects can be minimized using optimized end plate configuration at the exit of the shock tube, yet this is accompanied by secondary loading that is not representative of the free-field blast. Blast wave profile can be tailored using transition, conical, and suddenly expanded sections. We observe oscillations in the blast wave profile for suddenly expanded configuration. Locations outside the shock tube are affected by jet-wind effects because of the sudden expansion, barring a narrow region at the exit. For the desired overpressure yield inferred in bTBI, obtaining positive phase durations of <1 msec inside the shock tube, which are sought for studies in rodents, is challenging. Overall, these results underscore that replicating free-field blast conditions using a shock tube involves tradeoffs that need to be weighed carefully and their effect on injury outcomes should be evaluated during laboratory bTBI investigations.

Spectroscopic Assessment of Shock Wave Resistance on ZnO Nanorods for Aerospace Applications

Shock wave recovery experiments have been performed on a few nano-materials so far and the results show that it is very much possible to obtain tangible evidence for the stability of the materials at exposed conditions which is similar to that of the one prevailing at extreme environmental conditions. The title material of ZnO nanorods (ZnO NRs) have been synthesized by hydrothermal method and shock wave recovery experiment has been employed for ZnO NRs by utilizing a table-top pressure driven shock tube. For the present research work, we intend to investigate the optical and molecular vibrational characteristics of ZnO NRs at shocked conditions using UV-DRS and Raman spectroscopy, respectively. UV-DRS spectroscopic study reveals that the title material is highly stable in the visible region whereas its transmittance is slightly reduced in the UV region. The optical absorption of ZnO NRs is found to be increasing from 0.64 to 0.95 with respect to the number of shock pulses. The plot of the direct band gap shows that no phase transformation has occurred in ZnO NRs. Raman spectroscopic studies also reveal that ZnO NRs have stable crystalline system against the impact of shock waves. Due to the outstanding optical and structural properties, ZnO NRs are suggested for the space-related device applications.

Numerical and experimental study on mechanical behaviour of the AlSi10Mg aluminium structures manufactured additively and subjected to a blast wave

The paper is related to energy absorptive properties of additively manufactured metallic cellular structures. The samples of Honeycomb, Auxetic, rhomboidal Lattice and a regular Foam are subjected to a dynamic compression due to the blast tests. The cuboidal samples are manufactured by the Direct Metal Laser Sintering (DMLS) method using AlSi10Mg aluminium powder. The experimental tests are performed by means of an Explosive Driven Shock Tube (EDST). The measured results of the transmitted forces in relation to the shortening of the samples allow to analyse the deformation processes of each selected geometry. In addition, the evaluation of the structural responses leads to identification of the structure properties, such as the equivalent stress over equivalent strain or the energy absorption per a unit of mass. Moreover, the process of compression is modelled numerically using the explicit code LS-DYNA R9.0.1. The obtained simulations provide the complete analysis of the experimentally observed mechanisms.

Shock wave induced defect engineering on structural and optical properties of pure and dye doped potassium dihydrogen phosphate crystals

Abstract Based on the importance of the shock recovery experiments, the authors report the structural and optical properties of pure and 0.001 M dye-doped potassium dihydrogen phosphate (KDP) crystals for virgin and shock wave loaded samples. Rhodamine B and Methylene blue dyes are selected as dopants to be doped with KDP crystal for the present investigation. The test crystals of pure and doped KDP crystals are grown by slow evaporation technique and cut and polished crystals of (200) face are used for the present investigation. Table-top pressure driven shock tube is utilized for the shock wave generation and the used functional Mach number is 1.7. Virgin and shock wave loaded test crystals’ surface morphology, structural properties and optical transmissions are observed using optical microscope, powder X-ray diffractometer and UV-Visible spectrometer, respectively. Crystalline nature and optical transmission of pure and doped KDP crystals are found to have reduced by the impact of shock waves. It occurs due to the enhancement of defect concentration on the surface of the test crystals. From the observed results, we assert that the pure KDP crystal is relatively more stable to shock wave induced damage compared to doped KDP crystals as reflected by structural and optical studies.

Sticking dust and micrometeorite particles on to ices at high impact velocities - Implications for astrochemical ice enrichment

Impact events are inevitable to date both within the inner and outer regions of the Solar System. Such impact events dominate the surface modifications of most of the airless bodies. Regardless of the destructive nature of impact events, the birth of few moons in the Solar System are known to be the by-products of impacts. Moreover, particle aggregation from relatively low velocity impacts (from nm to μm sized dust particles) are thought to be the reason behind the growth of planetesimals. While considering impact events in the colder regions of the Solar System the role of molecular ices in planetesimal aggregation cannot be neglected. Therefore, to understand the role of such small particle impacts over icy bodies, we investigated the sticking of dust particles on to ices in the higher velocity impact regime, 100–300 ​m ​s−1, using a modified hand driven shock tube (Reddy Tube). Grains of brick, basalt and powdered turmeric, graphite and fullerene soot particles were fired on to the CO2 ice targets. Meteorite samples (Sulagiri and Allende) were used to mimic the real micrometeorite impacts on to dry ice. The particles of different sizes and impact angle are found to significantly affect the sticking pattern. The impact area was observed to be coated by the impacting material. Lesser micron sized particles were observed to penetrate into the ice layers and the larger ones eroding them. Results suggest that astrochemical ices can be chemically enriched by high velocity dust/micrometeoroid impacts.

Measurement of “Shock Wave Parameters” in a Novel Table-Top Shock Tube Using Microphones

A new manually operated pressure driven shock tube is proposed and demonstrated. Shock wave-associated parameters like velocity, Mach number, pressure, and temperature are computed using acoustic method. Experiment involves manually loading train of pressure pulses into a driver tube using a bicycle pump. The high pressure buildup in driver tube ruptures the diaphragm at critical pressure and generates a propagating shock wave in the driven section coupled with sensor section in which a couple of microphones are separated by a fixed distance. The propagating shock wave acoustical profile is recorded and its arrival time lag is measured using sound recording software. In a conventional method, piezo-electric pressure sensors are utilized to measure both pressure and time lag of shock wave between the sensors. In the proposed method, microphones are utilized to measure time lag of shock wave with sampling frequency of 768 KHz using computer supporting audio software. Utilizing time data, the said shock wave parameters are evaluated and reported. The performance of the proposed shock tube is compared with manually operated piston-driven Reddy tube.

CFD analysis of shock tube for blast impact testing

Shock tube is an experimental apparatus used to impart shock loading for testing various materials and designs. Shock loading induced by the shock tube is a safer alternative to conventional blast impact testing. Blast testing is critical for material selection, particularly in critical military structures exposed to blasts or shock waves. A compressed gas driven shock tube with a diaphragm separating the driver and driven section is used in the present study. Diaphragms of three different thicknesses (2 mm, 3 mm and 4 mm) are selected for the analysis. The maximum threshold pressure in the driver section increased with an increase in diaphragm thickness. Analytical equations are used to calculate the peak reflected pressure and energy which is incident at the end of the driven section. Computational fluid dynamics (CFD) simulation is performed on commercial software ANSYS Fluent 19.0. The reflected pressure–time graphs were compared with experimental tests to validate the CFD results. The CFD simulation was used to visualize various stages of the shock tube experiment by studying the pressure contours of the shock wave. The CFD results provided the parameters required for the calculation of the incident energy. The maximum incident energy available at the end of the driven section using diaphragm thickness 4 mm was 46.72 KJ. This value was 1.73 and 4.67 times that of the maximum incident energy obtained using diaphragm of thickness 3 mm and 2 mm respectively.

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.

Effect of shock waves on structural and dielectric properties of ammonium dihydrogen phosphate crystal

Abstract In this research article, the authors pay attention to investigate the effect of structural and dielectric properties of ammonium dihydrogen phosphate (ADP) crystal under pre and post shock loaded conditions. A shock wave of Mach number 1.9 was utilized for the present investigation which was generated by a table-top pressure driven shock tube. The crystalline nature and grain size variations were estimated by powder X-ray diffraction technique. The grain size of post shock wave loaded ADP crystal is found to be larger than that of the pre shock wave loaded ADP crystal. The dielectric properties of the pre and post shock loaded crystals were analyzed by impedance analyzer as a function of frequency (1 kHz–1 MHz) at ambient temperature. The dielectric constant is observed to be varying from 346 to 362 at the frequency of 400 kHz for pre and post shock wave loaded ADP crystals, respectively. The obtained results suggest that shock waves can be an alternate tool to tailor the physical properties of materials without creating any change in the original crystal system and surface morphology.