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This document is a summary of selected topics from the 29th International Colloquium on the Dynamics of Explosions and Reactive Systems (ICDERS) held in Siheung, Korea in July 2023. The conference focused on the dynamic aspects of reactive systems and included presentations on explosions, detonations, ignition, turbulent combustion, and other topics in combustion. The current issue of the journal Shock Waves includes ten papers that were presented at the conference, covering areas such as shock tube design, shock wave methane pyrolysis, detonation physics, and rotating detonation engine propulsion systems. The papers originated from China, India, Japan, Poland, and the USA. The authors and reviewers are thanked for their contributions to this issue. [Extracted from the article]

This thematic issue of the Shock Waves International Journal focuses on blast exposure research in military training environments. The editors aim to shed light on the complex nature of blast exposures and their effects on the human body, including health complications such as traumatic brain injury (TBI) and post-traumatic stress disorder (PTSD). The issue includes research papers from experts in blast physics, engineering, biochemistry, physiology, and clinical diagnostics. The goal is to better understand the health outcomes of blast exposures and develop safety standards and mitigation strategies to protect military personnel. The editors hope that this issue will contribute to ongoing investigations and improvements in safety standards for blast exposure. [Extracted from the article]

The current issue includes nine papers that fall into the following broad topic areas, mainly dealing with detonation wave dynamics. The current issue includes papers dealing with combustion in high-speed flow and shock waves, detonation, and deflagration-to-detonation transition, whose authors elected to submit to I Shock Waves i . This issue contains selected papers that were presented at the 28th International Colloquium on the Dynamics of Explosions and Reactive Systems (ICDERS) held in Naples, Italy, on June 19-24, 2022. [Extracted from the article]

Explosive breaching is a tactic operational professionals use to gain rapid entry and tactical advantage. This tactic exposes individuals to repeated low-level blasts (LLB), overpressure exposure generally occurring from user-directed munitions. The experimentation described in this paper highlights the need for further research into implementing explosives in tactical situations, specifically in confined areas, and the effects on individuals exposed. While current safety calculations predict peak pressures from an open-air detonation, this study incorporates the impulse of the total explosive event in a confined space. Sixteen explosive events were conducted to measure peak overpressures of the total duration of the event using pencil probes and flush mount-type sensors. These pressure sensors measured detonations at distances greater than or equal to the calculated minimum safe distances (MSD). The study compares these data with the Hopkinson–Cranz scaling law, the Weibull formula, and Kingery–Bulmash (KB) predictions. Additionally, a scaled mouse-to-human model for developing mild traumatic brain injury (mTBI) using pressure vs. impulse (P–I) graphs demonstrates areas of concern in the collected data. Results show that at distances exceeding the MSD, with personal protective equipment (PPE), and at pressures lower than those considered safe, mTBI is possible. Peak overpressures were measured to be 2.5 times higher than safety thresholds and impulses as high as 274 kPa ms. Confined area detonations produced 1.2–1.4 times greater pressures than open-air detonation measurements. Individuals who undergo breaching training will likely experience multiple exposures of this nature throughout their career, often occurring in rapid succession. [ABSTRACT FROM AUTHOR]

Blast deafness and balance disorders are common consequences of modern warfare and terrorist actions. A predictive evaluation system can assist commanders in quickly gathering information on the incapacitation of combat personnel. However, a critical challenge to this goal was to clarify the dose–response relationship between the blast parameters and the severity of auditory and vestibular dysfunction. This paper describes the algorithms for a prediction model. We performed blast experiments to obtain data on animal auditory/vestibular dysfunction under different overpressures. Peak overpressure and positive phase duration of the blast wave were obtained by pressure measurements. The severity of auditory and vestibular dysfunction was established by the auditory brainstem response test, behavioral rating, and vestibular-evoked myogenic potentials tests. Test data were analyzed using receiver operating characteristic (ROC) curves and logistic regression analysis to obtain the overpressure limits for auditory/vestibular function and logistic regression curves for severity separately. The ROC curve analysis showed that the overpressure limit for the auditory function was 32.635 kPa and the vestibular function was 96.275 kPa. Logistic regression fitted curves illustrated the dose–response relationship between the coefficient K, normalized by peak overpressure and positive phase duration, and the risk probability of auditory and vestibular disfunction. The prediction model for the risk of auditory and vestibular disfunction severity (mild/moderate/severe) has been established based on the overpressure limit and dose–response relationship. [ABSTRACT FROM AUTHOR]

Towards a better characterization of the increasing blast overpressure threat, person-borne sensors are being considered for large military population segments potentially subjected to explosive blast and firing of crew served weapons. Training and field data, tracked longitudinally across a soldier's entire career, can help with the diagnosis of blast injuries and the improvement of standard operating procedures for both explosive forced entry and large weapons firing. However, a current challenge with person-born blast dosimeters resides with the position of the overpressure sensors themselves. Often, the sensors are not fully exposed to the blast locally, resulting in pressure measurements not representative of the blast conditions surrounding an individual. While fielding multiple individual and uncoupled dosimeter units around the body increases the likeliness of catching the representative blast exposure, issues arise from differences in internal clock, potential partial triggering, and the complexity of merging data from different sources. Instead, integrating multiple overpressure sensors pointing in different directions, within a single device that captures and records all data simultaneously, proves highly beneficial for data analysis and interpretation. This paper presents algorithms that combine the overpressure data collected from such multiple coupled sensors for each blast event to minimize the effect of blast directionality. In particular, an algorithm estimating the equivalent side-on blast overpressure is presented, facilitating injury estimates from existing established blast injury models adapted for the outputs from the blast dosimeters. An algorithm is also presented that estimates the orientation or provenance of an explosive blast relative to the soldier. [ABSTRACT FROM AUTHOR]

The present work is a numerical follow-up on our published experimental paper on shock ignition of aluminium particle clouds in the low-temperature regime. The in-house multi-phase regularized smoothed particle hydrodynamics (MP-RSPH) code is used to perform numerical simulations with an increasing degree of complexity, looking at single-phase, inert, and reactive particles in separate simulations. The first part of the paper gives a short description of the additional physics added to the code. Based on the experimental results, the numerical code is then used to estimate the particle temperature at the time of ignition. Results from simulations with three different numerical descriptions, the diffusive, kinetic, and total burn rates, are then compared to the experimental results. The two diffusive burn rate simulations (K &H and O &H) show the best fit to the experimental results. The burn rate formula based on our experimental data (O &H) is preferred, since it has the gas temperature dependency included and does not require additional parameter adjustments. The results from the numerical simulations support the theory that the observed aluminium particle cloud burning process is diffusive, as indicated in the experimental paper. [ABSTRACT FROM AUTHOR]

A very short survey of research conducted in Poland on the development of the rotating detonation engine (RDE) is presented. Initial studies conducted in cooperation with Japanese partners lead to development of a joint patent on RDE. Then, an intensive basic and applied research was started at the Institute of Heat Engineering of the Warsaw University of Technology. One of the first achievements was the demonstration of performance of the rocket engine with an aerospike nozzle utilizing continuously rotating detonation (CRD), and research was directed into development of a small turbofan engine utilizing such a combustion regime. These activities promoted international cooperation and stimulated RDE development not only in Poland but also in other countries. A research directed to measure and calculate flow parameters as well as to analyze the use of liquid fuels was conducted. In the Institute of Aviation in Warsaw, research on the application of the CRD to turbine engines as well as rocket, ramjet, and combined cycle engines was carried out. In the paper, a special emphasis is given to international cooperation in this area with partners from many countries engaged in the development of the pressure gain combustion to propulsion systems. [ABSTRACT FROM AUTHOR]

The ongoing study of blast waves and blast wave mitigation continues to play an essential role in protecting structures and personnel. The methodology, however, for capturing far-field blast waves in large-scale tests has remained largely unchanged for three decades, relying on large arrays of pressure transducers connected by hundreds of meters of cabling and requiring a considerable amount of time to set up. This paper evaluates the use of a modern low-cost microprocessor with high computational power to capture blast waves with sufficient fidelity to provide scientists and engineers with credible data. The system utilizes an ARM Cortex M7 processor as an experimental data acquisition (DAQ) system for measuring far-field blast waves in an open-air blast arena at sampling speeds of up to 1.8 Msps (megasamples per second). The experimental system's performance was evaluated by comparing it to a traditional commercial system used for measuring blast waves. The comparison showed an average Spearman correlation coefficient r of 0.928 between the two systems, suggesting a low variance between the commercial and experimental DAQ systems. This suggests that, despite its simplicity, the experimental system is an effective and low-cost alternative for accurately measuring blast waves. [ABSTRACT FROM AUTHOR]

Experimental results on the interactions between a single water droplet and a shock wave propagating at Mach number above 4 are presented in this paper. A detonation-driven shock-tube test facility is used to work within a Mach range at M = 4.3 (high-supersonic regime) and M = 10.6 (hypersonic regime), for which the maximum studied dimensionless times T are up to 9.4 and 5.5, respectively. For both Mach ranges, the initial droplet diameters typically vary between 430 and 860 μ m and the associated Weber numbers vary from 5 × 10 4 to 11 × 10 4 . Ultra-high-speed cameras are used to record the evolution of the water droplet when the shock wave impacts it. Until T ≈ 2.5 , the qualitative and quantitative analyses of our frames show that the initial diameter as well as the Mach number studied have an apparent weak influence on the droplet dimensionless displacement. Beyond this time, the results for M = 10.6 are more dispersed than the data for M = 4.3 revealing a possible effect of the droplet size. One of the main results of this paper is that the droplet disappearance occurs at T = [ 4.5 –5.5] for M = 10.6 , while some mist is still present at T > 9 for M = 4.3 . We note also that the droplet is always supersonic for M = 10.6 whereas it becomes subsonic at T ≈ 3.5 for M = 4.3 . [ABSTRACT FROM AUTHOR]

In this paper, we continue our research on the numerical study of convergence to steady-state solutions for a new class of finite volume weighted essentially non-oscillatory (WENO) schemes in Zhu and Shu (J Comput Phys 349:80-96, 2017), from tensor product meshes to triangular meshes. For the case of triangular meshes, this new class of finite volume WENO schemes was designed for time-dependent conservation laws in Zhu and Qiu (SIAM J Sci Comput 40(2):A903-A928, 2018) for the third- and fourth-order versions. In this paper, we extend the design to a new fifth-order version in the same framework to keep the essentially non-oscillatory property near discontinuities. Similar to the case of tensor product meshes in Zhu and Shu  (2017), by performing such spatial reconstruction procedures together with a TVD Runge-Kutta time discretization, these WENO schemes do not suffer from slight post-shock oscillations that are responsible for the phenomenon wherein the residues of classical WENO schemes hang at a truncation error level instead of converging to machine zero. The third-, fourth-, and fifth-order finite volume WENO schemes in this paper can suppress the slight post-shock oscillations and have their residues settling down to a tiny number close to machine zero in steady-state simulations in our extensive numerical experiments. [ABSTRACT FROM AUTHOR]

Contrary to the conventional chemical propulsion systems based on the controlled relatively slow (subsonic) combustion of fuel in a combustor, the operation process in pulsed detonation engines (PDEs) and rotating detonation engines (RDEs) is based on the controlled fast (supersonic) combustion of fuel in pulsed and continuous detonation waves, respectively. One of the most important issues for such propulsion systems is the choice of fuel with proper reactivity and exothermicity required for a sustained and energy-efficient operation process. Presented in the paper are the results of thermodynamic calculations of the detonation parameters of boron- and aluminum-containing compounds (B, B 2 H 6 , B 5 H 9 , B 10 H 14 , Al, AlH 3 , Al(C 2 H 5 ) 3 , and Al(CH 3 ) 3) in air and water. The results demonstrate the potential feasibility of using the considered compounds as fuels for both air- and water-breathing transportation vehicles powered with PDEs and RDEs. As a verification of the reliability of the calculated results, the detonation parameters of diborane, aluminum, and isopropyl nitrate in air were compared with experimental data available in the literature. [ABSTRACT FROM AUTHOR]

Traditionally, Pitot rake test models have been used to take time- and spatially resolved impact pressure measurements in impulse facilities for flow characterisation. When expansion tubes are used for the study of hypervelocity planetary entry phenomena, generally the post-shock flow in the test section strongly radiates. This paper outlines a simple method which uses a high-speed camera in addition to a conventional Pitot rake to improve estimates of experimental test time and core flow size by imaging post-shock radiative emission over the probes in the Pitot rake. This method can also be used with specific narrow bandpass optical filters to examine when the emission from key species remains constant in the test flow in both time and space. The selection and suitability of various optical filters for a high-enthalpy Earth entry scenario are examined in this paper, as well as the effect of radiation from flow contamination. Experimentally, it was found that the radiative emission generally rises quite abruptly at the end of the test time and sometimes in situations where the pressure remains constant. It was also seen that different optical filters focusing on different spectral features can show their abrupt rise at different times, giving differing values for the end of the test time. Unfiltered measurements were found to be compromised by contaminant radiative emission which was seen to be randomly distributed in time and space towards the end of the test time. [ABSTRACT FROM AUTHOR]

A hybrid wing body (HWB) concept is being considered by NASA as a potential subsonic transport aircraft that meets aerodynamic, fuel, emission, and noise goals in the time frame beyond 2035. While the concept promises advantages over a conventional wing-and-tube aircraft, it poses unknowns and risks, thus requiring in-depth and broad assessments. Specifically, the configuration entails a tight integration of the airframe and propulsion geometries; the aerodynamic impact has to be carefully evaluated. With the propulsion nacelle installed on the (upper) body, the lift and drag are affected by the mutual interference effects between the airframe and nacelle. The static margin for longitudinal stability is also adversely changed. In the present paper, a design approach is developed in which the integrated geometries of airframe (HWB) and propulsion are accounted for simultaneously in a simple algebraic manner, via parameterization of the planform and airfoils at the design sections of the wing body. This paper presents a design of a 300-passenger aircraft that employs distributed electric fans for the propulsion. The trim condition for stability is achieved through the use of the wing tip twist angle. The geometric shape variables are determined through the adjoint optimization method by minimizing the drag while subjecting them to lift, pitching moment, and geometry constraints. An Euler model-based aerodynamic shape optimization is employed to save the design cost for the evaluation of the static margin and longitudinal stability, while the performance of the optimized configuration is evaluated by the RANS model coupled with a drag decomposition method to assess the true aerodynamic performance. The design results clearly show the influence on the aerodynamic characteristics of the installed nacelle and trimming for stability. A drag minimization with the trim constraint yields a reduction of 10 counts in the drag coefficient from the baseline design N3-X configuration, which is comparable with 2000 lbs more payload on a conventional subsonic civil transport airplane. [ABSTRACT FROM AUTHOR]

The pressure gain combustion in wave rotors has the potential to significantly enhance the performance of gas turbine engines. Wave rotor design focuses on understanding the complex behavior of rotating channels, which is challenging due to high rotational speeds. To investigate the influence of different working conditions on the unsteady process within the wave rotor combustor, a simplified 24-channel model was established to study both the unsteady flow and the wave dynamics. The calculations indicate that, for the current port position adopted and a rotor speed of 4000 rpm, backflow occurs at the inlet port for various inlet pressures. By analyzing the working sequence of the wave rotor combustor, it is found that the inlet port does not close in time when the pre-compression wave returns. This delay results in reflected expansion waves or compression waves moving within the channel, which affect a portion of the pressure gain, leading to a damped sinusoidal trend in the pressure profiles within the channel. The optimal pre-pressurization effect can be achieved at a rotor speed of 2000 rpm for the test conditions considered, and the total pressure gain achieved was 6.3%. By adding hot-jet ignition, it is found that the shock wave and flame interact at least five times in the current simulation. The shock–flame interaction can greatly accelerate the process of chemical reactions. After the fourth interaction, the shock wave achieved local coupling with the flame, forming a local high-pressure area of 4 bar, verifying the effectiveness of the wave rotor as a constant-volume supercharging device. [ABSTRACT FROM AUTHOR]

The author reflects on several papers discussed at 24th international colloquium held on July 28 to August 2, 2013 which took place in Taipei, Taiwan. He talks about the dynamic aspects of explosions and reactive systems. The colloquium featured the organization head Steven S. Shy of National Central University and Yei-Chin Chao of National Cheng-Kung University of Taiwan. Also included the current issue dealing with papers on combustion and shock waves.

The paper describes the dual behavior observed for hydrogen peroxide when added to hydrogen-air detonating mixtures. The effect of the addition of hydrogen peroxide on NO x emissions and critical detonation parameters was evaluated for H 2 air mixtures using one-dimensional ZND calculations. Hydrogen peroxide acts as an ignition promoter and is shown to significantly enhance the detonation chemistry when added in small concentrations. It alters the ignition chemistry of an underlying detonation wave without affecting the bulk thermodynamic properties. The main objective of the present study is to evaluate the ignition promotion and NO x mitigation effects of hydrogen peroxide in gaseous detonations when it is added to hydrogen-air mixtures in small and large concentrations. In the current work, the diminishing sensitizing potential of hydrogen peroxide when added in large amounts (up to 10%) is also reported. The results show a visible effect on ignition promotion up to 20,000 ppm. At concentrations higher than 20,000 ppm of H 2 O 2 , further reduction in the induction length was found to be minimal. The NO x emissions were found to decrease for stoichiometric and fuel-lean H 2 -air mixtures, whereas the NO x concentration was found to increase for fuel-rich mixtures with the addition of hydrogen peroxide. Thus, the dual behavior exhibited by H 2 O 2 is shown to be advantageous as it could potentially mitigate NO x emissions at high temperatures for fuel-lean and stoichiometric hydrogen-air mixtures and, at the same time, could sensitize the given mixture for applications in detonation-based combustors. [ABSTRACT FROM AUTHOR]

An important phenomenon in the gas–liquid two-phase mixtures is a sudden change in the flow that may lead to transition of the flow regime from non-homogeneous slip flow to homogenous flow. This phenomenon is called mixing shock and has been investigated by several researchers. In the present paper, a more comprehensive model is proposed by including the entrainment ratio in the governing equations. Moreover, parametric studies are performed to assess the importance of this parameter in different conditions. The results of the present study indicate that at Euler numbers less than four the effect of gas mass flow is insignificant. However, at higher Euler numbers the differences of the present and previous models are noticeable. Since two possible solutions for the aftershock state exist, four criteria—entropy change across the shock, possibility of an expansion shock, positivity of the Euler number, and choking flow condition—are considered to identify the correct solution. The results indicate that the flow after the shock could only be of a subsonic type, and the mixing shock is compressive. A comparison of the possible realizable zones for the developed model and the previous models indicates that the developed model predicts a larger area for the realizable solution of the mixing shock. A comparison between analytical results and experimental data shows that the developed model predicts reasonable results. [ABSTRACT FROM AUTHOR]

The aim of the present paper was to report on an experimental study of the characterization of a blast wave initiated by a solid explosive and its interaction with a rigid obstacle in the form of a hemicylinder. Pressure transducers located along the path of the blast wave and high-speed imaging allow (1) the measurement of the overpressure at different locations and (2) the characterization of the blast wave inception, propagation, and reflection off the hemicylinder. The scaling effect has been investigated by performing experiments in two different facilities, where one is at twice the scale of the other. [ABSTRACT FROM AUTHOR]

This paper is written in honor and memory of my esteemed friend and colleague, Meng-Sing Liou, with whom I worked closely in the 1990s on the development of AUSM-family schemes and their extensions to reactive, "all-speed," and multi-phase flows. The purpose of this paper is to revisit the thought processes and concepts that led to the rapid evolution of the AUSM family as a highly efficient, highly accurate method for discretization of the Euler equations and their various extensions. No new results are presented; rather, the focus is on (re-)discovering the common threads that link the various members of the AUSM family. Special attention is given to the strategies that lead to accurate results at all flow speeds, and some reviews of more current work in this area are presented. The paper concludes with a few reflections, personal and otherwise, relating to my interactions with Meng over the years and to my view of the essential elements of AUSM-family schemes. [ABSTRACT FROM AUTHOR]

This paper presents experimental data on incident overpressures and the corresponding impulses obtained in the test section of an explosively driven 10∘ (full angle) conical shock tube. Due to the shock tube's steel walls approximating the boundary conditions seen by a spherical sector cut out of a detonating sphere of energetic material, a 5.3-g pentolite shock tube driver charge produces peak overpressures corresponding to a free-field detonation from an 816-g sphere of pentolite. The four test section geometries investigated in this paper (open air, cylindrical, 10∘ inscribed square frustum, and 10∘ circumscribed square frustum) provide a variety of different time histories for the incident overpressures and impulses, with a circumscribed square frustum yielding the best approximation of the estimated blast environment that would have been produced by a free-field detonation. [ABSTRACT FROM AUTHOR]

Experimental results are presented for a rotating detonation engine supplied with liquid kerosene and preheated air without liquid or gaseous additions to the propellant mixture. Various combustion modes for the generic combustor geometry design were observed—from deflagration, through pulsed combustion and high-frequency instabilities, to stable detonation propagation. Attention was paid to detonation stability (if present), its characteristics, and the propulsive performance of the combustor with a focus on specific thrust and pressure gain through thrust and outlet total pressure measurement. These parameters measured for the observed modes were compared. The stability of the detonation combustion proved not to be critical to achieve high performance of the combustion chamber. For example, high performance was achieved for combustion modes with high-frequency instabilities. [ABSTRACT FROM AUTHOR]

This paper examines the effect of an asymmetrical energy source impact on the flow around supersonic aerodynamic bodies in a viscous heat-conducting gas (air) at Mach 2.5. The simulations are based on the Navier–Stokes equations with temperature-dependent viscosity and thermal conductivity. The dynamics of density, pressure, temperature, and heat fluxes were analyzed. Specific emphasis is placed on the effects of viscosity and thermal conductivity. Self-sustained oscillations of the flow parameters, lift and drag forces, and heat fluxes were obtained and studied. The mechanism of these oscillations was established, and the conditions of their presence in a flow in relation to the energy source characteristics and location were researched. Possible approaches for elimination of these oscillations were discussed. [ABSTRACT FROM AUTHOR]

In this paper, we provide the experimental evidence of a free-standing conical shock and the compressive confocal characteristics region in the Busemann intake flow. The experiments are carried out in the DRDC Trisonic Wind Tunnel at freestream Mach number 3.0 with a Busemann ring model. The Taylor-McColl equations are integrated to obtain the Busemann streamline and hence the inner surface of the Busemann ring. The CFD analysis of the flow using a locally adaptive unstructured Euler finite-volume code is in agreement with the experiments. [ABSTRACT FROM AUTHOR]

In this paper, we present results from spontaneous ignition of aluminium particle clouds in a series of shock tube experiments. For all experiments, the shock propagates along a narrow pile of 40- μ m aluminium particles. The study includes shock Mach numbers in the range from 1.51 to 2.38. The results are visualised using photographic techniques and pressure gauges. The combination of two Phantom high-speed video cameras and a beamsplitter allows a compact schlieren setup mounted together with a dark-film high-speed camera. While the schlieren technique allows the shock features to be identified, the dark-film camera is used to capture the ignition and burning of the aluminium particle clouds. Based on extensive image processing and shock tube relations for reflected shocks, spontaneous ignition of the aluminium particle cloud is found to take place for reflected shock gas temperatures above 635 K. For increasing Mach numbers, we find a decreasing trend for the ignition delay. Additionally, the burning time is observed to decrease with increasing Mach number, indicating that the burning process is more efficient with increasing gas temperature. [ABSTRACT FROM AUTHOR]

An introduction is presented which discusses topics within the issue including shock waves, isotropic turbulence, and vortex methods.

This paper presents the second part of a study aiming to accurately characterise a Mach 10 scramjet test flow generated using a large free-piston-driven expansion tube. Part 1 described the experimental set-up, the quasi-one-dimensional simulation of the full facility, and the hybrid analysis technique used to compute the nozzle exit test flow properties. The second stage of the hybrid analysis applies the computed 1-D shock tube flow history as an inflow to a high-fidelity two-dimensional-axisymmetric analysis of the acceleration tube. The acceleration tube exit flow history is then applied as an inflow to a further refined axisymmetric nozzle model, providing the final nozzle exit test flow properties and thereby completing the analysis. This paper presents the results of the axisymmetric analyses. These simulations are shown to closely reproduce experimentally measured shock speeds and acceleration tube static pressure histories, as well as nozzle centreline static and impact pressure histories. The hybrid scheme less successfully predicts the diameter of the core test flow; however, this property is readily measured through experimental pitot surveys. In combination, the full test flow history can be accurately determined. [ABSTRACT FROM AUTHOR]

Large-scale free-piston driven expansion tubes have uniquely high total pressure capabilities which make them an important resource for development of access-to-space scramjet engine technology. However, many aspects of their operation are complex, and their test flows are fundamentally unsteady and difficult to measure. While computational fluid dynamics methods provide an important tool for quantifying these flows, these calculations become very expensive with increasing facility size and therefore have to be carefully constructed to ensure sufficient accuracy is achieved within feasible computational times. This study examines modelling strategies for a Mach 10 scramjet test condition developed for The University of Queensland’s X3 facility. The present paper outlines the challenges associated with test flow reconstruction, describes the experimental set-up for the X3 experiments, and then details the development of an experimentally tuned quasi-one-dimensional CFD model of the full facility. The 1-D model, which accurately captures longitudinal wave processes, is used to calculate the transient flow history in the shock tube. This becomes the inflow to a higher-fidelity 2-D axisymmetric simulation of the downstream facility, detailed in the Part 2 companion paper, leading to a validated, fully defined nozzle exit test flow. [ABSTRACT FROM AUTHOR]

Crystals of energetic materials, such as 1,3,5,7-Tetranitro-1,3,5,7-tetrazocane (HMX), embedded in plastic binders are the building blocks of plastic-bonded explosives (PBX). Such heterogeneous energetic materials contain microstructural features such as sharp corners, interfaces between crystal and binder, intra- and extra-granular voids, and other defects. Energy localization or "hotspots" arise during shock interaction with the microstructural heterogeneities, leading to initiation of PBXs. In this paper, high-resolution numerical simulations are performed to elucidate the mechanistic details of shock-induced initiation in a PBX; we examine four different mechanisms: (1) shock-focusing at sharp corners or edges and its dependency on the shape of the crystal and the strength of the applied shock; (2) debonding between crystal and binder interfaces; (3) collapse of voids in the binder located near an HMX crystal; and (4) the collapse of voids within HMX crystals. Insights are obtained into the relative contributions of these mechanisms to the ignition and growth of hotspots. Understanding these mechanisms of energy localization and their relative importance for hotspot formation and initiation sensitivity of PBXs will aid in the design of energetic material-driven systems with controlled sensitivity, to prevent accidental initiation and ensure reliable performance. [ABSTRACT FROM AUTHOR]

PTFE/Al/W granular composite is a kind of impact-initiated energetic material and may well enhance damage to the impacted targets. To gain insight into response behavior of PTFE/Al/W granular composite under different loadings, the combined approach of experiments and theoretical analyses is used in this paper. More specifically, the combinations of quasi-static compression, dynamic tests, and ballistic impact experiments are conducted. Cylindrical PTFE/Al/W granular composite specimens, with a density of 7.7 g/cm 3 and a diameter of 10 mm, are fabricated by cold press molding, sintering, and cooling. Moreover, a high-speed imaging technique is used to record response process of the specimens in ballistic impact experiments. The experimental and analytical results show that the response behavior of PTFE/Al/W granular composite is significantly influenced by the loading strain rate. When the strain rate is less than 3.6 × 10 3 s - 1 , only mechanical response is observed in the quasi-static compression and dynamic tests. However, when the strain rate is higher than 4 × 10 4 s - 1 , the chemical reaction is found in the ballistic impact experiments. Furthermore, chemical response shows an enhanced trend with increasing of the loading strain rate. [ABSTRACT FROM AUTHOR]

Launching large (> 1 g) well-characterized projectiles to velocities beyond 10 km s - 1 is of interest for a number of scientific fields, but is beyond the reach of current hypervelocity launcher technology. This paper reports the development of an explosively driven light-gas gun that has demonstrated the ability to launch 8-mm-diameter 0.36-g magnesium projectiles to 10.4 km s - 1 . The implosion-driven launcher (IDL) uses the linear implosion of a pressurized tube to shock-compress helium gas to a pressure of 5 GPa, which then expands to propel a projectile to hypervelocity. The launch cycle of the IDL is explored with the use of down-bore velocimetry experiments and a quasi-one-dimensional internal ballistics solver. A detailed overview of the design of the 8-mm launcher is presented, with an emphasis on the unique considerations which arise from the explosively driven propellant compression and the resulting extreme pressures and temperatures. The high average driving pressure results in a launcher that is compact, with a total length typically less than a meter. The possibility to scale the design to larger projectile sizes (25 mm diameter) is demonstrated. Finally, concepts for a modified launch cycle which may allow the IDL to reach significantly greater projectile velocities are explored conceptually and with preliminary experiments. [ABSTRACT FROM AUTHOR]

The paper presents unique blast experiments in reference to scientific literature and official standards. Experimental scenarios reflect a hypothetical realistic combat situation of a human being covered from a blast wave behind a rigid building corner. In the scenario assumed, the overpressure loads affect the lungs while the person is standing or the eardrums while the person is kneeling at the aiming position. The paper presents 27 free-field experiments measuring the overpressure loads. All the measurements were taken behind the right angle of the rigid wall. Two masses of TNT were considered: 200 g and 400 g. In the selected cases, a low test-to-test variability of the measured data was observed. Detailed plots of overpressure versus time are presented for various distances behind the building corner and TNT charge masses. Peak overpressure versus positive impulse plots are also demonstrated. Furthermore, the safety thresholds regarding different locations behind the building corner are defined for the considered explosive masses. [ABSTRACT FROM AUTHOR]

Surrogate models for hotspot ignition and growth rates were presented in Part I (Nassar et al., Shock Waves 29(4):537–558, 2018), where the hotspots were formed by the collapse of single cylindrical voids. Such isolated cylindrical voids are idealizations of the void morphology in real meso-structures. This paper therefore investigates the effect of non-cylindrical void shapes and void–void interactions on hotspot ignition and growth. Surrogate models capturing these effects are constructed using a Bayesian Kriging approach. The training data for machine learning the surrogates are derived from reactive void collapse simulations spanning the parameter space of void aspect ratio, void orientation (θ) , and void fraction (ϕ) . The resulting surrogate models portray strong dependence of the ignition and growth rates on void aspect ratio and orientation, particularly when they are oriented at acute angles with respect to the imposed shock. The surrogate models for void interaction effects show significant changes in hotspot ignition and growth rates as the void fraction increases. The paper elucidates the physics of hotspot evolution in void fields due to the creation and interaction of multiple hotspots. The results from this work will be useful not only for constructing meso-informed macroscale models of HMX, but also for understanding the physics of void–void interactions and sensitivity due to void shape and orientation. [ABSTRACT FROM AUTHOR]

An experimental evaluation of the transmission of shock waves from a detonating gas mixture in a 0.5-in-inner-diameter open-ended tube into an inert atmosphere is described in this paper. Stoichiometric H 2 /O 2 at 1 atm was used as the reactive gas medium. Results from in-tube diagnostics indicated successful deflagration-to-detonation transition (DDT), which leads to an overdriven detonation before exiting the tube at near Chapman–Jouguet (CJ) conditions. Out-of-tube diagnostics characterized the transmission of the shock wave into the surrounding environment, where the shock wave decays into an acoustic wave as it travels away from the tube exit. A mathematical treatment of overpressure and time-of-arrival data allowed for a direct analytical description of the transmitted shock wave's transient velocity. This description is combined with a first-principles gas-dynamics treatment of the moving normal shock wave to describe the conditions behind the attenuating shock wave. This work furthers the understanding of shock transmission from an open-ended detonation tube and provides a theoretical framework to estimate the resulting conditions. [ABSTRACT FROM AUTHOR]

It is well established that detonation in a confined environment can lead to the formation of a Mach stem along the walls or after diffraction on an obstacle. As the formation of this kind of reflection can produce higher levels of overpressure, it is important to study and understand its formation and propagation for safety purposes in the event of an accidental or intentional detonation. This paper reports an experimental approach to the propagation of a Mach stem formed by the diffraction of a shock wave around an obstacle and compares the height of the triple point with an empirical model from Kinney and Graham. In predictive models, the Mach stem is formed by a charge detonating above the ground, which is why its evolution is different from a Mach stem formed after diffraction. The shock waves were generated by the detonation of a stoichiometric hemispherical charge of propane-oxygen. The visualization was coupled with 30 pressure sensors to record pressure history data in order to determine the influence of the Mach stem on wall overpressure inside a small-scale model, representing two rooms in a building separated by an open door. [ABSTRACT FROM AUTHOR]

A historical summary of the early classic papers in shock compression science is presented with the purpose of establishing the foundations for more recent studies of shock waves in solids. The major (largely theoretical) works of the period from 1808 to 1949 have been previously brought together into a single collection [Johnson and Chéret, Springer-Verlag, New York, 1998]. Important papers on shock waves in condensed matter from 1948 to the present were not included in the collection, largely because of their relatively easy accessibility. This paper provides a supplement to the original collection allowing research workers and historians to trace the major developments leading to the establishment of the unique field of shock compression in solids. [ABSTRACT FROM AUTHOR]

This paper explains research examining processes accompanying underwater explosions near the free surface. Particular attention is paid to the effect of heterogeneous nucleation on cavitating flow induced by underwater explosions near the free surface. Variation of the size spectrum of produced bubbles and influence of this process on flow structure are studied. The cavitating liquid is considered as a two-phase bubbly medium described in the framework of the Euler-Lagrange approach treating the carrier phase (liquid) as a continuum and the dispersed phase (bubbles) as a set of test particles. More detailed descriptions of a mathematical model, numerical method, and algorithm validation are observed in the authors' previous paper [see, Petrov and Schmidt (Exp Thermal Fluid Sci 60:367-373, 2015)]. [ABSTRACT FROM AUTHOR]

This paper describes a new device to decouple free-piston driver recoil and its associated mechanical vibration from the acceleration tube and test section of The University of Queensland's X3 expansion tube. A sliding joint is introduced to the acceleration tube which axially decouples the facility at this station. When the facility is fired, the upstream section of the facility, which includes the free-piston driver, can recoil upstream freely. The downstream acceleration tube remains stationary. This arrangement provides two important benefits. Firstly, it eliminates nozzle movement relative to the test section before and during the experiment. This has benefits in terms of experimental setup and alignment. Secondly, it prevents transmission of mechanical disturbances from the free-piston driver to the acceleration tube, thereby eliminating mechanically-induced transducer noise in the sensitive pressure transducers installed in this low-pressure tube. This paper details the new design, and presents experimental confirmation of its performance. [ABSTRACT FROM AUTHOR]

The aim of this study is to characterize the interaction of a shock wave with an obstacle. The effect of the length of the obstacle on the shock wave propagation and maximum overpressure is investigated. Several previous studies investigated the use of obstacles such as porous materials, grids, pseudo-perforated walls, triangular wedges, or multi-obstacles as a way to mitigate blast intensity. Here, the focus is on the interaction of an incident shock wave on a single-plate obstacle. This obstacle can be seen as a wall or a low-rise building. The paper presents a small-scale experimental study. The blast wave is created by the detonation of a hemispherical gaseous charge. It is characterized by pressure sensors and a high-speed camera. The pressure sensors record the overpressure and arrival time. The propagation, reflection, and diffraction of the shock wave are analyzed from the pictures produced during the visualization tests. [ABSTRACT FROM AUTHOR]

Terrorist organizations around the world have used explosives on many occasions to carry out attacks in urban centers. The victims and injuries in these attacks are often due to structural collapses and the impact of debris. This threat leads researchers to study the performance of ordinary building systems exposed to extreme impulsive loads. Confined masonry buildings are a widely used construction system in seismic zones in many parts of the world and have been widely studied under seismic loads. On the other hand, studies of the response to out-of-plane impulsive loads, such as those caused by intentional or accidental explosions, are scarce. In this paper, results of three experimental explosions at different scaled distances are presented. The explosives on and 1 m above the ground were used. Confined masonry walls with and without openings were tested. The complex interaction between air blast and ground shock was analyzed. Levels of damage obtained with different scaled distances are presented. The results are compared with iso-damage curves. [ABSTRACT FROM AUTHOR]

In this paper, the process of vertical downward underwater supersonic gas jets and its acoustic characterization is investigated. This is because the acoustic properties of these jets are not well characterized to date; numerical simulations are conducted for three different jet conditions, for one case with an underexpanded jet and for two cases with overexpanded jets. For numerical validation, experimental overall sound pressure level measurements are available, giving a good agreement between simulations and experiments. The numerical data provide information about the formation of the jet pattern depending on the depth of penetration of the gas jet into the water. Adaptive filtering technique and time–frequency analyses are applied to evaluate the numerical acoustic data. Combined with the study of evolution of flow structures, the spectrum and spectrogram indicate that the formation of shock waves and its destruction by vibrations of the jet elevate pressure and sound pressure fluctuations in the flowfield. As a result of these investigations, it follows that computational fluid dynamics could be applied to well understand the physics behind underwater gas jet noise, and it is proposed to use computational fluid dynamics for further studies of gas jets blowing into water. [ABSTRACT FROM AUTHOR]

This paper reports the experiments on the shock standoff distance (SSD) around spheres flying at Mach numbers from slightly below 1.0. Spheres of the same diameter but three different densities were launched in a ballistic range by a light-gas gun, and the flow field around each sphere was measured by optical visualization. The purpose of this study is to investigate how projectile deceleration influences the SSD by comparing the results for projectiles of the same shape, size, and Mach number but different densities. The location history of the sphere center is obtained by fitting a formula derived from the equation of motion of a decelerating object, and the history of the instantaneous projectile Mach number is obtained by differentiating this formula.The SSDs of the projectiles with different densities are the same at higher Mach numbers, but different at lower Mach numbers, and the SSD decreases with decreasing projectile density. Seemingly, because projectile deceleration is related to the flow unsteadiness, steady flow cannot be assumed in the present range of Mach number with the different SSDs. At Mach numbers close to one, that of the propagating detached shock wave is higher than that of the flying projectile. [ABSTRACT FROM AUTHOR]

Artificial viscosity is used in the computer simulation of high Reynolds number flows and is one of the oldest numerical artifices. In this paper, I will describe the origin and the interpretation of artificial viscosity as a physical phenomenon. The basis of this interpretation is the finite scale theory, which describes the evolution of integral averages of the fluid solution over finite (length) scales. I will outline the derivation of finite scale Navier-Stokes equations and highlight the particular properties of the equations that depend on the finite scales. Those properties include enslavement, inviscid dissipation, and a law concerning the partition of total flux of conserved quantities into advective and diffusive components. [ABSTRACT FROM AUTHOR]

Broadband shock-associated noise (BBSAN) is a particular high-frequency noise that is generated in imperfectly expanded jets. BBSAN results from the interaction of turbulent structures and the series of expansion and compression waves which appears downstream of the convergent nozzle exit of moderately under-expanded jets. This paper focuses on the impact of the pressure waves generated by BBSAN from a large eddy simulation of a non-screeching supersonic round jet in the near-field. The flow is under-expanded and is characterized by a high Reynolds number Rej=1.25×106 and a transonic Mach number Mj=1.15. It is shown that BBSAN propagates upstream outside the jet and enters the supersonic region leaving a characteristic pattern in the physical plane. This pattern, also called signature, travels upstream through the shock-cell system with a group velocity between the acoustic speed Uc-a∞ and the sound speed a∞ in the frequency-wavenumber domain (Uc is the convective jet velocity). To investigate these characteristic patterns, the pressure signals in the jet and the near-field are decomposed into waves traveling downstream (p+) and waves traveling upstream (p-). A novel study based on a wavelet technique is finally applied on such signals in order to extract the BBSAN signatures generated by the most energetic events of the supersonic jet. [ABSTRACT FROM AUTHOR]