Single Shock Research Articles

Kinetics of Zr under shock-ramp compression

<p indent=0mm>The dynamics of Zr under shock-ramp wave loading was studied with experiments and simulations. The shock-ramp wave compression experiments of Zr with different loading thermodynamics path were carried out with photonic Doppler velocimetry (PDV) and compact pulsed power generator CQ-4. The velocity wave profiles show that Zr undergoes shock and then ramp wave compression in the loading section. When the shock pressure reaches about <sc>10 GPa,</sc> the velocity profile contains phase transition information. However, the phase transition information could not be observed when the shock pressure is up to <sc>25 GPa.</sc> It is a single shock wave when the shock pressure is at <sc>44 GPa.</sc> The experimental results are simulated with the Hayes multi-phase equation of state and the non-equilibrium phase transition kinetic model, which can well describe the physical processes of the elastoplastic transition and the phase transition in the loading section.

Experimental and modeling study of the oxidation of F-24 jet fuel, and its mixture with an iso-paraffinic synthetic jet fuel, ATJ

Single pulse shock tube experiments were conducted to determine the oxidative decomposition products of F-24. Experiments were performed at 50 bar nominal pressure, 7 ms nominal reaction time, temperatures ranging from 800 K to 1300 K, initial fuel concentration of 655 ppm, and equivalence ratio of 0.93. F-24 is Jet A with additives. Experiments with Jet A were performed at similar conditions to show there were no main differences between the two jet fuels in order to use chemical kinetic models developed for Jet A for the simulation of F-24. Additional experiments for pure ATJ and ATJ/F-24 mixture at matching conditions were performed to analyze the effect of mixing a kerosene-based jet fuel with a synthetic jet fuel. ATJ is a synthetic alcohol-to-jet fuel that can be classified as Jet A. Gas chromatography (GC) and two-dimensional GC (GCxGC) was used to analyze the products of the chemical reactions and to determine their mole fractions. The speciation measurements were compared against three different jet fuel surrogate models. A detailed and a reduced model from the CRECK Modeling Group, and the second-generation surrogate model developed in house by Malewicki et al. The ability of the kinetic model to capture the effect of varying the experimental test conditions on the evolution of intermediate species is discussed and kinetic analyses have been conducted to identify the important reaction pathways.

Theoretical Study of the Reaction of Hydrogen Atoms with Three Pentene Isomers: 2-Methyl-1-butene, 2-Methyl-2-butene, and 3-Methyl-1-butene.

This paper presents a comprehensive potential energy surface (PES) for hydrogen atom addition to and abstraction from 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene and the subsequent ß-scission and H atom transfer reactions. Thermochemical parameters for species on the Ċ5H11 potential energy surface (PES) were calculated as a function of temperature (298-2000 K), using a series of isodesmic reactions to determine the formation enthalpies. High-pressure limiting and pressure-dependent rate constants were calculated using Rice-Ramsperger-Kassel-Marcus theory with a one-dimensional master equation. A number of studies have highlighted the fact that C5 intermediate species play a role in polyaromatic hydrocarbon formation and that a fuel's chemical structure can be key in understanding the intermediate species formed during fuel decomposition. Rate constant recommendations for both Ḣ atom addition to, and H-atom abstraction by Ḣ atoms from, linear and branched alkenes have subsequently been proposed by incorporating our earlier work on 1- and 2-pentene, and these can be used in mechanisms of larger alkenes for which calculations do not exist. The current set of rate constants for the reactions of Ḣ atoms with both linear and branched C5 alkenes, including their chemically activated pathways, are the first available in the literature of any reasonable fidelity for combustion modeling and are important for gasoline mechanisms. Validation of our theoretical results with pyrolysis experiments of 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene at 2 bar in a single pulse shock tube (SPST) were carried out, with satisfactory agreement observed.

Detailed experimental and kinetic modeling study of toluene/C2 pyrolysis in a single-pulse shock tube

Abstract A combined experimental and kinetic modeling study is carried out to explore the influences of acetylene and ethylene addition on the species formation from toluene pyrolysis. Experiments are conducted separately with four different argon-diluted binary toluene/C2 mixtures in a single pulse shock tube at a nominal pressure of 20 bar over a temperature range of 1150−1650 K. All the experimental mixtures contain about 100 ppm toluene and different amounts of C2 fuels (50, 216, 459 ppm acetylene and 516 ppm ethylene). Species concentrations as a function of the temperature are probed from the post-shock gas mixtures and analyzed through the gas chromatography/gas chromatography-mass spectrometry techniques. A kinetic model is developed, which successfully predicts the absolute species concentration measurements as well as the changes brought by the varied fuel compositions. With the neat fuel decomposition profiles as a reference, both fuel components exhibit increased reactivity in the pyrolysis of all studied binary mixtures, indicating the existence of obvious synergistic effects. In particular, such effects become more remarkable when increasing the initial acetylene concentration. This essentially results from the addition-elimination reaction of a toluene fuel radical and a C2 fuel molecule leading to a C9 molecule and a hydrogen atom. Indene is identified as the predominant C9 product in all studied cases, and its peak concentrations sharply increase with the initial acetylene contents in toluene-acetylene pyrolysis. On the other hand, indane, produced from the addition-elimination reaction between benzyl and ethylene, is only detected at trace levels in toluene/ethylene pyrolysis. This indicates a relatively weaker interaction between benzyl and ethylene, compared to that of benzyl and acetylene. Apart from the increased concentrations of hydrogen atoms and C9 aromatics, interactions between toluene and C2 fuels also directly result in a reduced level of C7 radicals in the reaction system. Overall, PAH species can be divided into two groups according to the way their peak concentrations varying with the initial fuel compositions. For those largely depending on benzyl reactions, such as bibenzyl, biphenylmethane, fluorene and phenanthrene, the peak concentrations decrease with the added C2 fuels. In contrast, increasing trends are observed in the peak concentrations of the PAHs which rely on indenyl as a precursor, including naphthalene, methyl-indene, benzofulvene and acenaphthalene.

Molecular insights into shock responses of amorphous polyethylene

Shock responses of amorphous polyethylene (APE) were characterized utilizing two different types of methodology, direct non-equilibrium molecular dynamics (NEMD) and multi-scale shock technique (MSST). Providing a detailed physical view of the shock front itself, pico-second time resolved evolution of plasticity behind the shock front was explored by NEMD through simulating piston driven shock compression. The induced-shock propagation and reflection were visualized according to the evolution of the particle displacement, particle velocity field and pressure field. Exponential relations between the compression rate in a shock wave and the hydrodynamic pressure, in addition, the thickness of shock front and the hydrodynamic pressure were clarified, which quantitatively indicate the shrinkage of shock front resulted from higher compression strength under larger piston velocity. On the other hand, in addition to reproducing the final compressed states, the thermo-dynamical state variables behind the leading shock front were captured by MSST with a much smaller computational cell with enough efficiency and accuracy. Hugoniot relations were obtained to predict the bulk sound speed and two material constants indicating the compressibility with reliable values compared with the existing results. Temperature-dependency was clarified as that high temperature reduces the bulk sound speed with low density and improves the compressibility of material. The temperature-sensitivity of compressibility weakens or even disappears during the transition from glassy state to rubbery state. The critical shock velocity, which equals to the bulk sound speed at a given temperature, was specified to guarantee stable shock wave instead of quasi-isentropic wave propagation in APE. Only a single plastic shock wave with a steep front travelling at a constant velocity greater than the bulk sound speed generates in APE, resulting in the over-driven in the material.

Observational Evidence for Fast Mode Periodic Small-scale Shocks: A New Type of Plasma Phenomenon

Abstract We show observational evidence for a new form of collisionless shock in interplanetary space near Mars, small-scale shocks with periodic spacings. Pickup of new ionized hydrogen atoms in a magnetic field aligned with the solar wind direction causes the generation of a magnetosonic wave train through an ion beam instability. The waves have a frequency close to the local proton gyrofrequency. This is a similar physical process as for the formation of cometary plasma waves/turbulence. However, for the case of proton pickup near Mars, each individual magnetosonic wave cycle develops into a small-scale shock. So there is a string of fast mode shocks formed with proton gyroperiod spacings. These small-scale shocks display dissipation in the ions and dispersive whistlers. A fraction of ions trapped/reflected at the small-scale shocks are accelerated by the motional electric field. Observational results demonstrate that periodic shocks can perform the same functions as a single supercritical shock in a high-speed flow.

Three Questions Regarding Impulse Responses and their Interpretation Found from Sign Restrictions

When sign restrictions are used in SVARs impulse responses are only set identified. If sign restrictions are just given for a single shock the shocks may not be separated, and so the resulting structural equations can be unacceptable. Thus, in a supply demand model, if only signs are given for the impulse responses to a demand shock this may result in two supply curves being in the SVAR. One needs to find the identified set so that this effect is excluded. Granziera el al’s (2018) frequentist approach to inference potentially suffers from this issue. One also has to recognize that the identified set should be adjusted so that it produces responses to the same size shock. Finally, because researchers are often unwilling to set out sign restrictions to separate all shocks, we describe how this can be done with a SVAR/VAR system rather than a straight SVAR.

Abstract 254: High Shock Efficacy and Algorithm Performance for a 150J Biphasic Waveform AED Used by Lay and BLS Responders During Out-of-hospital Cardiac Arrest

Introduction: Effective AED defibrillation of out of hospital cardiac arrest (OHCA) depends on the safe and effective identification of shockable rhythms, and on delivery of effective defibrillation energy. This report summarizes rhythm detection performance and shock efficacy during OHCA uses of Philips HeartStart Home and OnSite AEDs using non-escalating 150 J therapy. Methods: A convenience sample of 185 OHCA AED patient uses were reviewed by clinical experts. All analysis periods that resulted in AED rhythm advisories (Shock Advised or No Shock Advised) were annotated. Shockable rhythm categories include VF and polymorphic VT/flutter. Non-Shockable rhythm categories include normal sinus rhythm, other rhythms (e.g., atrial fibrillation/flutter, bradycardia, SVT, idioventricular, bundle branch block), and asystole. Intermediate rhythms (benefits of defibrillation are limited or uncertain) were not included. Post-shock rhythm was categorized as shockable, non-shockable, or undeterminable (rhythms corrupted by CPR artifact or pads removal within 5-s of shock delivery). Shock success was defined as conversion to a non-shockable rhythm within 5-s post-shock. Results: A total of 487 analysis periods resulted in AED rhythm advisories, with 175 annotated as Shockable and 312 Non-shockable. Sensitivity and specificity (n/N, Exact 95% CI) were 97.7% (171/175, 94.3%, 99.4%) and 100% (312/312, 98.8%, 100.0%) respectively. A total of 165 shocks were delivered to 100 patients with 5 undeterminable post-shock rhythms. The remaining 160 shocks were delivered to 156 Shockable rhythm episodes. All shock efficacy was 96.9% (155/160, 92.9%, 99.0%): 150 episodes converted to non-shockable rhythms after one shock (96.2% (150/156, 91.8%, 98.6%)); 154 after two shocks (98.7% (154/156, 95.4%, 99.8%)); and 155 after three shocks, the first two of which were undeterminable (99.4% (155/156, 96.5%, 100.0%)). The remaining episode had a failed first shock, followed by an undeterminable second shock, which was the last shock of the use. Conclusion: For these 150J fixed-energy AEDs, OHCA defibrillation is safe (100% specificity), and effective (97.7% sensitivity; 96.2% single shock effectiveness; 98.7% after two shocks; 99.4% after three shocks).

The shocking state of apatite and merrillite in shergottite Northwest Africa 5298 and extreme nanoscale chlorine isotope variability revealed by atom probe tomography

The elemental and chlorine isotope compositions of calcium-phosphate minerals are key recorders of the volatile inventory of Mars, as well as the planet’s endogenous magmatic and hydrothermal history. Most martian meteorites have clear evidence for exogenous impact-generated deformation and metamorphism, yet the effects of these shock metamorphic processes on chlorine isotopic records contained within calcium phosphates have not been evaluated. Here we test the effects of a single shock metamorphic cycle on chlorine isotope systematics in apatite from the highly shocked, enriched shergottite Northwest Africa (NWA) 5298. Detailed nanostructural (EBSD, Raman and TEM) data reveals a wide range of distributed shock features. These are principally the result of intensive plastic deformation, recrystallization and/or impact melting. These shock features are directly linked with chemical heterogeneities, including crosscutting microscale chlorine-enriched features that are associated with shock melt and iron-rich veins. NanoSIMS chlorine isotope measurements of NWA 5298 apatite reveal a range of δ37Cl values (−3 to 1‰; 2σ uncertainties <0.9‰) that is almost as large as all previous measurements of basaltic shergottites, and the measured δ37Cl values can be readily linked with different nanostructural states of targeted apatite. High spatial resolution atom probe tomography (APT) data reveal that chlorine-enriched and defect-rich nanoscale boundaries have highly negative δ37Cl values (mean of −15 ± 8‰). Our results show that shock metamorphism can have significant effects on chemical and chlorine isotopic records in calcium phosphates, principally as a result of chlorine mobilization during shock melting and recrystallization. Despite this, low-strain apatite domains have been identified by EBSD, and yield a mean δ37Cl value of −0.3 ± 0.6‰ that is taken as the best estimate of the primary chlorine isotopic composition of NWA 5298. The combined nanostructural, microscale-chemical and nanoscale APT isotopic approach gives the ability to better isolate and identify endogenous volatile-element records of magmatic and near-surface processes as well as exogenous, shock-related effects.

Active compression versus standard anterior-posterior defibrillation for external cardioversion of atrial fibrillation: A prospective randomized study

Electrical cardioversion is the first-line rhythm control therapy for symptomatic persistent atrial fibrillation (AF). Contemporary use of biphasic shock waveforms and anterior-posterior positioning of defibrillation electrodes have improved cardioversion efficacy; however, it remains unsuccessful in >10% of patients. The purpose of this study was to assess the efficacy of applying active compression on defibrillation electrodes during AF cardioversion. We performed a bicenter randomized study including patients referred for persistent AF cardioversion. Elective external cardioversion was performed by a standardized step-up protocol with increasing biphasic shock energy (50-100-150-200 J). Patients were randomly assigned to standard anterior-posterior defibrillation or to defibrillation with active compression applied over the anterior electrode. If sinus rhythm was not achieved at 200 J, a single crossover shock (200 J) was applied. Defibrillation threshold, total delivered energy, number of shocks, and success rate were compared between groups. We included 100 patients, 50 in each group. In the active compression group, defibrillation threshold was lower (103.1 ±49.9 J vs 130.4 ± 47.7 J; P = .008), as well as total delivered energy (203 ± 173.3 J vs 309 ± 213.5 J; P = .0076) and number of shocks (2.2 ± 1.1 vs 2.9 ± 1.2; P = .0033), and cardioversion was more often successful (48 of 50 patients [96%] vs 42 of 50 patients [84%]; P = .0455) than that in the standard anterior-posterior group. Crossover from the compression group to the standard group was not successful (0 of 2 patients), whereas crossover from the standard group to the compression group was successful in 50% of patients (4 of 8). Active compression applied to the anterior defibrillation electrode is more effective for persistent AF cardioversion than standard anterior-posterior cardioversion, with lower defibrillation threshold and higher success rate.

Factores para predecir los resultados de la litotricia por ondas de choque en pacientes pediátricos y validación externa de un nomograma

ObjectiveTo evaluate the accuracy of the Dogan nomogram in predicting stone-free (SF) rate after a single shock wave lithotripsy (SWL) session and evaluate factors that predict SWL results in children. Patients and methodsThe study included 68 patients under 18 years of age who had been treated with SWL for radiopaque upper urinary tract stones in our tertiary centre from January 2010 to December 2016. The median age is 50 (6-207) months and median follow-up period is 9 (4-50) months. Patients with known cystine stone disease, abnormal renal anatomy, urinary diversion and multiple stones located in different calyces were excluded like in the original nomogram study. SF status was evaluated by performing plain abdominal radiography and urinary ultrasonography 2 weeks after each SWL session. Patients who were completely free of stones were considered to be SF. Multiple logistic regression analyses were performed to determine the variables affecting SF status. The bootstrap method with 1,000 replicates was used for the external validity of a nomogram developed by Dogan. ResultsSF rates for each SWL session were determined as 54.4% (37/68) for the first session, 33.3% (7/21) for the second session and 55.6% (5/9) for the third session. Overall, the SF rate was 72.1% (49/68). Multiple logistic regression analysis showed positive and significant correlations of age and stone size with risk of SWL failure. The external calibration plot showed a nearly good validation with Dogan nomogram to predict SWL failure in first session. ConclusionOur study demonstrates that the Dogan nomogram can be used to predict the SF status after one session of SWL in pediatric patients.

Dispersive of propagation wave solutions to unidirectional shallow water wave Dullin–Gottwald–Holm system and modulation instability analysis

This article possesses modulation instability (MI) analysis and new exact wave solutions to unidirectional Dullin–Gottwald–Holm (DGH) system that describes the prorogation of waves in shallow water. The exact wave solutions in single and combined form like shock, singular, and shock‐singular are extracted by means of an innovative integration norm, namely, ‐expansion scheme. The periodic and plane wave solutions are also emerged. The constraint conditions which ensure the existence of solutions are discussed as well. Moreover, the choice of suitable parameters gives the three‐dimensional and two‐dimensional sketches, and furthermore, their contour plots are also drawn.

Experimental Research of Gasdynamic Liquid Drops Breakup in the Supersonic Flow with an Oblique Shock Wave

This paper is devoted to understanding gasdynamic liquid drops breakup in a supersonic flow with presence of an oblique shock wave. An experimental facility, diagnostic tools and an experimental methodology are presented as well as numerical simulations results. Computations and experiments were used to get flow parameters in the duct with supersonic flow at Mach numbers 2.0, 2.5, and 3.0. The droplets were made to interact with a single oblique shock wave generated by a wedge in the test section. Experimental data are obtained for the change in diameter of the droplets and the change in speed of droplets in a supersonic flow at the three Mach numbers. The data are presented for an initial Weber number over the range of 16–115. It is shown that the mass loss rate of droplets are quadratically related to the Weber number, irrespective of the presence of oblique shock.

Cyclonic Change: How Tracy Shaped Australian Loss Adjusters’ Break from Britain

The professional institutions of loss adjusting in Australasia were shaped by a range of postcolonial developments, including adhesion to the British badge of organizational prestige, the Royal Charter. The aim of this paper is to explore how a single exogenous shock to the institution of loss adjusting in Australia enhanced a sense of national identity, altering the future of those institutions. Our conclusions are based on over sixty interviews with loss adjusters in three countries and the archives of several Australasian loss adjusting institutions dating back to the late 1800s. Archival material included correspondence, meeting minutes, various memorandum, newspaper clippings, membership lists, criteria for barriers to entry, records of lobbying efforts, disciplinary actions, and educational material. Reus-Smit (2002, 2017), Bell (2009), and Rae (2017) have developed the understanding of the role collective cultural and national identities play in institutionalism, whereas Suddaby et al. (2007, 2011) have contributed to the theory of field-level institutional change. Building on the literature of Suddaby et al., this paper appraises how a single historic natural event triggered normative changes impacting the institution of loss adjusting in the region.

Variations in Constitutive Properties of the Fluid Elicit Divergent Vibrational and Pressure Response Under Shock Wave Loading.

We performed a characterization of the shock wave loading on the response of the specimen representing a simplified head model. A polycarbonate cylinder (2-in. outer diameter, wall thickness: 0.06 or 0.12 in.) was filled with two fluids: pure de-ionized water and 40% glycerol in water, which differ only slightly in their constitutive material properties. These two fluids were selected to represent the cerebrospinal fluid and cerebral blood, using their high strain rate viscosity as a primary selection criterion. The model specimen was exposed to a single shock wave with two nominal intensities: 70 and 130 kPa overpressure. The response of the model was measured using three strain gauges and three pressure sensors, one mounted on the front face of the cylinder and two embedded in the cylinder to measure the pressure inside of the fluid. We noted several discriminant characteristics in the collected data, which indicate that the type of fluid is strongly influencing the response. The vibrations of the cylinder walls are strongly correlated with the fluid kind. The similarity analysis via the Pearson coefficient indicated that the pressure waveforms in the fluid are only moderately correlated, and these results were further corroborated by Euclidean distance analysis. Continuous wavelet transform of pressure waveforms revealed that the frequency response is strongly correlated with the properties of the fluid. The observed differences in strain and pressure modalities stem from relatively small differences in the properties of the fluids used in this study.

Multiple paternity in the intertidal zone porcelain crabPetrolisthes cinctipesRandall, 1840 (Decapoda: Anomura: Porcellanidae) is a life-history strategy that increases fitness during heat stress

AbstractMultiple paternity is widespread across animal and plant taxa and can increase genetic diversity and enhance fitness, especially in unpredictable environments. A prior study of the intertidal zone porcelain crab, Petrolisthes cinctipes (Randall, 1840), found that most females carried polyandrous broods. We tested the hypothesis that multiple paternity in P. cinctipes enhances fitness through increased average brood tolerance to temperature stress. Embryonic survival of split broods (N = 27) was measured under ambient conditions and following a single one-hour heat shock at 30 °C. Two microsatellite loci were used to genotype embryos and mothers in order to distinguish multiple from single paternity in each brood. Mean overall hatching percentage did not differ between singly and multiply sired broods; however, when exposed to a heat-shock, single-sired broods experienced 11% lower hatching success. Though relative fitness was higher in single-sired broods under non-stressful conditions, extrapolation of our results to conditions where temperatures are at least 30 °C (present-day extremes for the California coast) for &amp;gt; 2 days of the embryonic brood period, multiply sired broods have a relative fitness that is approximately 24 times higher after 15 generations. Maternal quality (size) and the timing of the heat shock relative to developmental timing also influence the brood response to heat shock. Our results suggest that multiple paternity reduces embryo survival variance between ambient and heat-shock conditions and that polyandrous behavior could be an advantage for P. cinctipes in the thermally variable high-intertidal zone. We conclude that multiple paternity is an important strategy for increasing fitness by genetic diversification in organisms that experience severe and unpredictable levels of environmental stress.

Global solution to a three-dimensional spherical piston problem for the relativistic Euler equations

The study of spherically symmetric motion is important for the theory of explosion waves. In this paper, we consider a ‘spherical piston’ problem for the relativistic Euler equations, which describes the wave motion produced by a sphere expanding into an infinite surrounding medium. We use the reflected characteristics method to construct a global piecewise smooth solution with a single shock of this spherical piston problem, provided that the speed of the sphere is a small perturbation of a constant speed.

Shock–Boundary Layer-Interaction Control Through Recirculation in a Hypersonic Inlet

Abstract This technical brief presents a flow separation mitigation device, called cavity-recirculator that can be used to control flow separation during shock wave–boundary layer interaction (SBLI) in high-speed intake flows. The cavity-recirculator isolates the flow separation bubble generated at the SBLI spot, thereby thinning the boundary layer and reducing the blockage of the inviscid stream in the duct. The device has a potential application in scramjet engine intakes/isolators. The cavity-recirculator was tested on a single-ramp-compression intake model in a hypersonic shock tunnel, in a freestream of Mach 8 (±0.1). The device operation and effectiveness were assessed by flow visualization and pressure measurements in the test model. The measurements and visualization displayed a mitigation of flow separation through an improved flow field with a single shock train and the absence of flow separation shock, in the inlet.

A Fast-Response Calorimeter with Dynamic Corrections for Transient Heat Transfer Measurements

Robust fast-response transient calorimeters with novel calorimeter elements have attracted the attention of researchers as new synthetic materials have been developed. This sensor uses diamonds as the calorimeter element, and a platinum film resistance is sputtered on the back to measure the temperature. The surface heat flux is obtained based on the calorimetric principle. The sensor has the advantages of high sensitivity and not being prone to erosion. However, non-ideal conditions, such as heat dissipation from the calorimeter element to the surroundings, can lead to measurement deviation and result in challenges for sensor miniaturization. In this study, a novel transient calorimeter (NTC) with two different sizes was developed using air or epoxy as the back-filling material. Numerical simulations were conducted to explain the complex heat exchange between the calorimeter element and its surroundings, which showed that it deviated from the assumption of an ideal calorimeter sensor. Accordingly, a dynamic correction method was proposed to compensate for the energy loss from the backside of the calorimeter element. The numerical results showed that the dynamic correction method significantly improved the measurement deviation, and the relative error was within 2.3% if the test time was smaller than 12 ms in the simulated cases. Detonation shock tunnel experiments confirmed the results of the dynamic correction method and demonstrated a practical method to obtain the dynamic correction coefficient. The accuracy and feasibility of the dynamic correction method were verified in a single detonation shock tunnel and under shock tube conditions. The NTC calorimeter exhibited good repeatability in all experiments.

Shock train behavior affected by continuous Mach number variation of incoming flow

Experimental and numerical investigations have been performed to study the influence of continuous Mach number variation on the shock train. An adjustable Laval nozzle which could continuously change the throat area was developed to change the Mach number from 2.4 to 1.8. As the incoming flow Mach number decreased, the background waves moved upstream. The movement of positive and negative pressure gradient regions caused by background waves resulted in different pressure histories at different wall positions. The pressure history at a position could be used to determine whether shock reflection points passed through this position and how many shock reflection points passed through this position. During the Mach number decreasing, the shock train first moved downstream and then upstream, always accompanied by oscillations. Two types of oscillations and one type of jump movement were observed during the movement of shock train, and the first type of oscillation occurred interlaced with the second type of oscillation or jump movement. The first shock of shock train changed from X-shaped to λ-shaped due to the decreasing of Mach number. The structure of shock train head became more complicated when the first shock was λ-shaped, because the background shock would interfere with different parts of the λ-shaped shock. In addition, the mechanism of shock train movement affected by Mach number variation was discussed. It was found that the Mach number decreasing of incoming flow had two opposite effects on the shock train movement, including the decreasing of pressure boosting capacity of a single shock, which caused the shock train to move upstream, and the upstream movement of background waves, which caused the shock train to jump downstream. Whether the shock train moved upstream or downstream depended on which effect dominated.