Shock Wave Research Articles

On the Collision of Railcars as an Interaction of Soliton-like and Shock Wave-like Perturbations

Several new mathematical issues have been set for the development of high-speed transport, which can be solved in the framework of hydrodynamics to describe the process of hydrodynamics, creating effective rolling stock dampers. which requires the improvement and development of the corresponding mathematical apparatus. In this work, we use a hydrodynamic approach to find the density distributions of matter during railcar collisions at high speeds, which is important in light of the problems of high-speed transport. In our approach, we found an analytical solution to the obtained hydrodynamic equations for the one-dimensional case. The equations under study were obtained taking into account nonequilibrium processes. To find a solution to the hydrodynamic equations, the shock wave approximation is used, similar to the soliton solutions we considered earlier. Taking into account possible deviations from the results of a one-dimensional problem is considered. Such a reduction of solutions of hydrodynamic equations to shock waves has not been considered previously and may be of interest for a wide variety of applied problems. The resulting consideration of railcar collisions is important for solving problems of transport safety and technospheric safety.

High-bandwidth pressure field imaging of fin-generated shock wave–boundary layer interactions

The dynamics of a shock-induced separation unit generated by a 20 $^\circ$ sharp fin placed on a cylindrical surface in a Mach 2.5 flow was investigated. Specifically, the present work investigated the mechanisms that govern the mid-frequency range of separation shock unsteadiness in the fin shock wave–boundary layer interaction (SBLI) unit. Two-dimensional pressure fields were obtained over the cylinder surface spanning the entire fin SBLI unit using high-bandwidth pressure-sensitive paint at 40 kHz imaging rate that allowed probing the low- through mid-frequency ranges of the separation shock unsteadiness. The mean pressure field showed a progressive weakening of the separation shock with downstream distance, which is an artifact of the three-dimensional relief offered by the curved mounting surface. The root-mean-square (r.m.s.) pressure field exhibited a banded structure with elevated $p_{r.m.s.}$ levels beneath the intermittent region, separation vortex and adjacent to the fin root. The power spectral density (PSD) of the surface pressure fluctuations obtained beneath the intermittent region revealed that the separation shock oscillations exhibited the mid-frequency content over the majority of its length. Interestingly, neither the PSD nor the length of the intermittent region varied noticeably with downstream distance, revealing a constant separation shock foot velocity along the entire SBLI. The pressure fluctuation PSD beneath the separation vortex also exhibited the broadband peak at the mid-frequency range of the separation shock motions over the majority of its length within the measurement domain. By contrast, the region adjacent to the fin root exhibited pressure oscillations at a substantially lower frequency compared with the separation shock and the separation vortex. Two-point coherence and cross-correlation analysis provided unique insights into the critical sources and mechanisms that drive the separation shock unsteadiness. The separation vortex and separation shock dynamics were found to be driven by a combination of convecting perturbations that originated from the vicinity of the fin leading edge and the local interactions of the separated flow with the incoming boundary layer. The boundary layer locally strengthened or weakened the convecting pressure perturbations depending on the local momentum fluctuations within the boundary layer.

An experimental and kinetic modeling study on the auto-ignition of ammonia/butan-1-ol mixtures

Ignition delay times (IDTs) of ammonia(NH3)/butan-1-ol mixtures with NH3/butan-1-ol mole ratios of 100/0, 95/5, 90/10 and 70/30 were measured behind reflected shock waves in a shock tube over a range of experimental conditions: temperature range of 1100 – 2000 K, pressures of 0.14 and 0.5 MPa, equivalence ratios of 0.5, 1.0 and 2.0. A new NH3/butan-1-ol reaction mechanism, capable of predicting the experimental results reliably, was developed. Chemical kinetic analyses were performed with the model. It is demonstrated that increasing the content of butan-1-ol in the reaction system results in a non-linear trend of shortening on the IDTs of mixtures, adding 5 % molar fraction of butan-1-ol results in shortening rates of over 70 %. As the butan-1-ol blending ratio increases from 5 % to 30 %, the discrepancy in IDT of the mixture between equivalence ratios of 0.5 and 1.0 diminishes while it remains more pronounced between equivalence ratios of 1.0 and 2.0. The presence of butan-1-ol does not change the oxidation pathways of the NH3 mixture. R72(NH3 + M = NH2 + H + M) and R75(NH2 + HO2 = NH3 + O2) are key reactions to activate chain reactions of the NH3 mixture during the initial reaction stage, for a temperature of 1500 K, a pressure of 0.14 MPa, and an equivalence ratio of 1.0. Reactive radicals produced through the process of butan-1-ol oxidation result in a significant increase in the initial dehydrogenation consumption rate of NH3, by a factor of 5 ∼ 6 powers of ten, accelerating chain reactions.

The influence of the shock-to-reshock time on the Richtmyer–Meshkov instability in reshock

Experiments on the Richtmyer–Meshkov instability (RMI) in a dual driver vertical shock tube (DDVST) are described. An initially planar, stably stratified membraneless interface is formed by flowing air from above and sulfur hexafluoride from below the interface location using the method of Jones & Jacobs (Phys. Fluids, vol. 9, issue 1997, 1997, pp. 3078–3085). A random three-dimensional, multi-modal initial perturbation is imposed by vertically oscillating the gas column to produce Faraday waves. The DDVST design generates two shock waves, one originating above and one below the interface, with these shocks having independently controllable strengths and interface arrival times. The shock waves have nominal strengths of $M_L=1.17$ and $M_H=1.18$ for the shock wave originating in the light and heavy gas, respectively, with these strengths chosen to result in arrested bulk interface motion following reshock. The influence of the length of the shock-to-reshock time, as well as the order of shock arrival, on the post-reshock RMI is examined. The mixing layer width grows according to $h\propto t^\theta$ , where $\theta _H=0.36\pm 0.018$ (95 %) and $\theta _L=0.38\pm 0.02$ (95 %) for heavy and light shock first experiments, respectively, indicating no strong dependence on the order of shock wave arrival. Volume integrated specific turbulent kinetic energy (TKE) in the mixing layer versus time is found to decay according to $E_{tot}/\bar {\rho }\propto t^p$ with $p_H=-0.823\pm 0.06$ (95 %) and $p_L=-1.061\pm 0.032$ (95 %) for heavy and light shock first experiments, respectively. Notably, the 95 % confidence intervals do not overlap. Analysis on the influence of the shock-to-reshock time on turbulent length scales, transition criteria, spectra and mixing layer anisotropy are also presented.

Aerodynamic heating in hypersonic shock wave and turbulent boundary layer interaction

In hypersonic flight the shock wave and turbulent boundary layer interaction (STBLI) sharply increases wall heat transfer that intensifies the aerodynamic heating problems. In this work the STBLI is modelled by compression ramp flow with a Mach number of 5, a Reynolds number based on momentum thickness of 4652 and a wall to recovery temperature ratio of 0.5. The aerodynamic heat generation and transport mechanisms are investigated in the interaction based on theoretical analysis and direct numerical simulation (DNS) that agrees with previous studies. A prediction correlation of wall heat flux in STBLI is deduced theoretically and validated by some representative data including the present DNS, which improves the prediction accuracy and can be applied to a wider $Ma$ range compared with the canonical Q-P theory. The correlation indicates that the sharp increase of wall heat transfer in the STBLI can be explained by the boundary layer compression and the convection transport enhancement. Based on the DNS results, the aerodynamic heat generation and transport mechanisms are revealed in the separation, recirculation and reattachment zones in the STBLI. From this perspective, the peak heat flux can be further explained by the enhancement of near-wall turbulent energy dissipation, compression aerodynamic heat generation and the near-wall turbulent transport. The generation and transport of compression aerodynamic heat reveal the underlying mechanism of the strong correlation between the peak heat flux ratios and the pressure ratios in STBLIs.

Collapse of microbubbles over an elastoplastic wall

The collapse of a vapour bubble over a material surface has been widely studied over the past few decades, but a comprehensive and quantitative analysis of the cavitation dynamics and its effects on solid materials at the mesoscale (nanometre up to micrometre), which would be of particular interest in applications exploiting cavitation power, is still lacking. In this work, we adopt a diffuse interface model to describe the microbubble dynamics, and a dynamic plasticity model for the solid. The former is particularly suited to studying the rich phenomenology characterising bubble collapse at the mesoscale, which comprises transitions to supercritical conditions, emission and propagation of shock waves, generation of liquid microjets and topological transitions, whereas the latter is used to characterise the permanent plastic deformation caused by the bubble collapse, and has been augmented to consider inertial effects, to assess whether or not an interaction between elastic and plastic waves may influence the resulting deformation. Results concerning the collapse of a microbubble at different liquid overpressures and initial standoff ratios are discussed, and the elastoplastic wave propagation in the solid, together with plastic deformation, is studied for different cases, depending on elastic and plastic material parameters.

Efficient ROUND schemes on non-uniform grids applied to discontinuous Galerkin schemes with Godunov-type finite volume sub-cell limiting

Developing accurate, efficient and robust shock-capturing schemes on non-uniform grids remains challenging particularly when facing strong non-uniformity. Thus, we extend the unified normalised-variable diagram (UND) initially proposed by Deng (2023) [30] on uniform grids to non-uniform grids, and propose essentially non-oscillatory (ENO) and high-resolution regions in non-uniform grid UND. Based on the proposed UND, we formulate a high-resolution shock-capturing scheme termed ROUND (Reconstruction Operators on Unified-Normalise-variable Diagram) on non-uniform meshes. Unlike classic WENO (Weighted Essentially Non-Oscillatory) schemes applied to non-uniform grids, the ROUND scheme avoids the expensive calculation of smoothness indicators. The ROUND scheme is first applied to solve the scalar convection equation. The results reveal that the ROUND scheme significantly improves the numerical resolution and preserves the structure of the passively convected scalar compared to the TVD (Total Variation Diminishing) limiters. For capturing discontinuous solutions, the proposed ROUND scheme on non-uniform meshes surpasses the performance of the 5th-order WENO-JS scheme. The ROUND scheme is then integrated into discontinuous Galerkin (DG) with the FV subcell limiting method to enhance the numerical resolution at the subcell level while adhering to the discrete conservation law. The compactness and simplicity of the ROUND scheme on non-uniform grids are compatible with the DG method, known for its features such as compactness and flexibility of hp-refinement. The resulting DG method, utilising finite volume ROUND subcell limiting, is denoted as the DG/FV-ROUND scheme. To assess the accuracy and robustness of the DG/FV-ROUND scheme, we simulate high-speed compressible flows characterized by strong shock waves and small-scale flow structures. Comparative studies show the improved numerical resolution achieved by DG/FV-ROUND. Thus, this research demonstrates the efficacy and robustness of the ROUND scheme on non-uniform grids and affirms that incorporating high-resolution ROUND as subcell shock-capturing schemes can enhance the resolution of DG/FV methods.

Undercompressive phase transitions for the model of fluid flows in a nozzle with discontinuous cross-sectional area

Undercompressive phase transitions violating Lax shock inequalities in a model of fluid flows in a nozzle with discontinuous cross-section area are studied. The Riemann problem involving phase transitions is considered. Depending on the choice of admissibility criteria suitable for a specific application, one can obtain a Riemann solver, which may involve nonclassical shock wave. The resonance phenomenon is also observed as multiple shocks waves of the same speed can apparently appear in a single solution. The Riemann problem may admit a unique solution in some region, but may have up to three distinct solutions in other regions.

Exploring Nonlinear Dynamics in Intertidal Water Waves: Insights from Fourth-Order Boussinesq Equations

The fourth-order nonlinear Boussinesq water wave equation, which describes the propagation of long waves in the intertidal zone, is investigated in this study. The exact wave patterns of the equation were computed using the tanh method. As stability decreased, soliton wave structures were derived using similarity transformations. Numerical simulations supported these findings. The tanh method introduced a Galilean modification, leading to the discovery of several new exact solutions. Subsequently, the fourth-order nonlinear Boussinesq wave equation was transformed into a planar dynamical system using the travelling wave transformation. The quasi-periodic, cyclical, and nonlinear behaviors of the analyzed equation were particularly examined. Numerical simulations revealed that varying the physical parameters impacts the system’s nonlinear behavior. Graphs represent all possible examples of phase portraits in terms of these parameters. Furthermore, the study was proven to be highly beneficial for addressing issues such as shock waves and highly active travelling wave processes. Sensitivity analysis theory and the Lyapunov exponent were employed, offering a wide variety of linear periodic and first-frequency periodic characteristics. Sensitivity analysis and multistability analysis of the Boussinesq water wave equation were thoroughly investigated.

Quadruple-D score in the success rate of extracorporeal shock wave lithotripsy of renal stones in pediatric population.

Evaluation of the validity of the Quadruple-D score in the prediction of success in pediatric stone disease. Of the 292 children treated with SWL between 2007 and 2023, a total of 158 children who had adequate follow-up data and evaluated with non-contrast computed tomography before SWL, were included in the study. Parameters were calculated for each of the stone volume (SV), skin-to-stone distance (SSD), stone density (SD) and stone location (SL) variables. Receiver operator characteristic analysis was used to set cut-off values. Quadruple-D scores were calculated, and success rates were determined for each score. Stone-free status was determined as complete clearance after three months of final SWL. The median age of the study group was 8 (range 1 to 16). One hundred and one of the 158 (64%) children had stone-free status. Mean SV, SSD and SD values were significantly higher in SWL failed group than stone-free group after detecting cutoff values of 150 mm3, 6.7 cm, and 540 HU, respectively. Stone-free rates were detected as 19.6%, 24.7%, 37.2%, 76.2%, and 90.2% with the Quadruple-D scores of 0, 1, 2, 3 and 4 points. Quadruple-D scoring system can further improve Triple-D scoring system by adding stone position parameter to clarify SFR with a simple and easy calculation. We believe that the Quadruple-D score will have better clinical significance than the Triple-D scoring system in predicting the success of SWL in children.

Effects of the jet obstacle on flame acceleration and deflagration-to-detonation transition: A numerical perspective

As a new type of the detonation-promoting technology, the jet obstacle has attracted wide attention of researchers, but there are still many deficiencies in the current studies. Based on means of numerical analysis, the effects of jet velocity and the non-uniformity of the velocity distribution on flame acceleration and DDT (deflagration-to-detonation transition) processes are investigated in detail using the unsteady Reynolds average simulation method. The findings indicate that, with regard to flame acceleration, an increase in jet velocity will initially impede the acceleration of the flame to a certain extent. Nevertheless, the interaction between the flame and the jet gives rise to a complex multiple acceleration mechanism (such as the intensification of flow field perturbations within the channel, an augmented accumulation of premixed gases, an amplified virtual blocking effect, and an enlarged recirculation zone). This increased jet velocity serves to accelerate both the propagation of the flame and the detonation initiation process. The jet non-uniformity of the velocity distribution is also a vital factor to improve the DDT process. With the increase in the trend of non-uniformity changes in the jet velocity distribution (the continuous enhanced jets are used in this paper), the time and distance required for the detonation initiation of premixed gases are shortened. Furthermore, depending on the state of the shock wave, the detonation initiation processes in this paper all belong to the shock to detonation transition, which can be further classified into two categories: (I) detonation that induced by shock reflection; and (II) detonation that induced by shock focusing.

Self-organization of collisionless shocks: from a laminar profile to a rippled time-dependent structure

A collisionless shock structure results from the nonlinear interaction between charged particles and electromagnetic fields. Yet, a collisionless shock is globally governed by the mass, momentum and energy conservation requirements. A stable shock structure must ensure that the fluxes of the conserved quantities are constant on average, and, therefore, is determined by this necessity. Here, we study an observed high upstream temperature high Mach number shock and show that the conservation laws cannot be fulfilled unless the shock is spatially inhomogeneous along the shock front and time-dependent.

Clinical evaluation of the efficacy of focused extracorporeal shock-wave therapy in patients with cervical spondylosis: A randomized control trial.

Extracorporeal shock wave therapy (ESWT) has emerged as a contemporary modality in physiotherapy, demonstrating efficacy in addressing musculoskeletal disorders. Despite its potential, the clinical efficacy of ESWT in the context of cervical spondylosis remains understudied, with a dearth of robust empirical evidence. To bridge this gap, the present study was designed to evaluate the therapeutic impact of focused ESWT (fESWT) on pain alleviation and functional improvement in individuals afflicted with cervical spondylosis. A multicenter, randomized controlled clinical study was conducted, collecting data from 5 clinical studies on the treatment of cervical spondylosis with fESWT from June 2021 to March 2024. The inclusion criteria were patients diagnosed with cervical spondylosis, aged 20 to 70, without severe underlying diseases such as heart disease, hypertension, diabetes, etc. The exclusion criteria included pregnant women, nursing women, patients with bleeding tendencies, or those with cardiac pacemakers. The control group underwent a sham fESWT, while the experimental group received fESWT administered via the Duolith SD1 Tower device. The main observation indicators included the Visual Analogue Scale (VAS) for pain scoring, Neck Disability Index (NDI) scoring, cervical range of motion (ROM) scoring, and the Short Form-36 (SF-36) quality of life survey scoring. A total of 320 subjects were included in the study, with 160 in the experimental group and 160 in the control group. Post-treatment, the VAS and NDI scores in the experimental group were significantly lower than those in the control group (P < .05), while the cervical range of motion (ROM) and SF-36 scores were significantly higher than in the control group (P < .05). The overall treatment efficacy rate in the experimental group exceeded 90%, markedly higher than the approximately 70% rate in the control group (P < .05). There was no significant difference in the incidence of adverse reactions between the 2 groups. The fESWT has shown promising therapeutic effects in the treatment of cervical spondylosis. It effectively reduces patient pain, improves cervical function, and enhances the quality of life, making it worthy of clinical promotion and application.

Does the intervention for adhesive capsulitis in patients with diabetes differ from that for patients without diabetes?: A systematic review.

Adhesive capsulitis (AC) is often accompanied by pain and restriction in range of movement, which long lasting symptoms often have negative impact on patients' work and lives. Since diabetes mellitus (DM) is an independent risk factor for developing AC, and AC with DM have more limitations of joint motion than general people. The aim of the present study is to evaluate the difference of clinical efficacy between diabetes and non-diabetes, and to explore whether AC with diabetes need special intervention compared to non-diabetes. Pubmed NCBI and Embase were searched for studies published in the last 30 years. We conducted a literature search for terms regarding AC and DM on Pubmed NCBI and Embase. A total of 9 studies eligible for inclusion. The affected shoulders in these studies ranged from 26 to 135, 460 shoulders (551 participants) in total, including 166 shoulders in diabetic group and 394 shoulders in non-diabetic/idiopathic group. Interventions included shock wave therapy, hydrodilatation, arthroscopic capsular release, manipulation under cervical nerve root block. Evaluation indicators included pain, certain shoulder questionnaires, range of motion. Positive clinical efficacy were emerged after interventions between the 2 groups. The studies that better improvement of pain in non-diabetic/idiopathic group were 2 of 6, that of certain shoulder questionnaires were 4 of 8, that of range of motion were 3 of 6. Whether AC combined with DM or not, the current treatment could achieve positive clinical effectiveness and there is some statistical evidence show that the curative effect of AC combined with DM is worse than non-diabetic. In other words, the available evidence suggests that patients with DM might require additional rehabilitation measures with routine glycemic control.

Development of a methodology and design of a device for determining the Mach number of a supersonic flow

The paper presents the developed methodology and designed a device for determining the Mach number during supersonic gas outflow. An analysis of various methods for determining the Mach number was carried out, including measuring the pressure at the flow boundary, the use of shock waves, and the use of optical methods. A comparison was made of the accuracy of the readings when using the considered methods. Based on the results obtained, a technique for high-precision determination of the Mach number has been developed, including a combination of several independent measurement methods. A device has been designed that implements this measurement technique, and the results of experimental tests in a wind tunnel have been reviewed, including instrument readings, graphs and tables confirming the accuracy and reliability of the data obtained. Their accuracy and reliability are analyzed. Using the analysis, it is possible to ensure the selection of the most rational method for determining the Mach number at the initial stage of designing aircraft, such as airplanes, missiles, fighters, and UAVs. Accurate knowledge of the Mach number allows engineers to optimize the aerodynamic characteristics of the aircraft, ensure flight safety, improve engine efficiency and overall air transport performance. In addition, the Mach number is the most important criterion of similarity when modeling in aerodynamic research, which makes the developed methodology and device relevant not only for the design of aircraft, but also for a wide range of scientific and engineering research in the field of aeronautical technology. It is emphasized that the presence of a reliable method for determining the Mach number can significantly reduce the time and resources spent on testing and improving aircraft, and also contributes to the development of innovative technologies in the field of aviation and astronautics.

Traditional Plants Based Treatment for Kidney Stones: Insight into Herbal Drugs

The deposition of hard crystals created by mineral or salt buildup in the urine canal leads to kidney stones, a frequent urinary tract issue. Urine flow obstruction and excruciating discomfort can be caused by kidney stones. Numerous processes can lead to oxidative stress, which raises the probability of kidney stones developing. The inflammatory response that results from kidney stones forming exacerbates oxidative stress further, creating a vicious cycle. This urological condition, which affects both male and female populations, is becoming more widespread worldwide. Planning the volume of urine produced is a crucial stage in the elimination of kidney stones. Surgery such as shock wave lithotripsy (SWL) and ureteroscopy (URS) is used to treat conditions when the stone has ceased passing through and is causing excruciating discomfort. Because of their medicinal and antioxidant properties, as well as their active substances, medicinal plants have positive benefits on human health. Regrettably, end-stage renal disease is frequently the consequence of side effects brought on the traditional medications used to treat nephrolithiasis. Kidney stones can be avoided by controlling nutrition intake, medication usage, and diet. Agents that are urolithotriptic are medicinal herbs. Examining the natural plants that are utilized to treat the illness is the goal of this review. Finding natural plants that can be used to cure kidney stones was made easier by this review. Keywords: Kidney stones, Urolithiasis, diuresis, herbal drug, calcium oxalate stone

Comparative Analysis of Cellulite Treatment Modalities: A Systematic Review.

Cellulite is a highly prevalent and aesthetically distressing skin condition. Whilst there are a variety of treatment modalities, none are definitively established. This systematic review aims to assess invasive and noninvasive treatment modalities for cellulite management. The review protocol was published and registered a priori (PROSPERO CRD42022359334). A comprehensive electronic search for relevant randomised controlled trials, (RCTs) was performed in CENTRAL, MEDLINE, Embase and Web of Science databases. Study quality and risk of bias were assessed using Cochrane's risk of bias tool, respectively. Overall, 753 studies were initially identified, of which 24 randomised controlled trials (RCTs) satisfied the eligibility criteria with a total of 2084 patients with a mean follow-up of 3.33 ± 13.4weeks. Evaluated interventions included mechanical stimulation, topical therapy, shock wave therapy (SWT), laser and light-based devices, radiofrequency therapy, subcutaneous injectables, and ultrasound. SWT emerged as a standout intervention, demonstrating a consistent cellulite reduction score of 2.07 ± 0.39 across four studies. Radiofrequency therapy exhibited a statistically significant reduction of thigh circumference (- 2.09cm, p < 0.001) and subcutaneous tissue thickness (- 2.23cm, p < 0.001). Subcutaneous injectables, specifically collagenase Clostridium histolyticum-aaes, demonstrated a statistically significant improvement in the clinician-reported photonumeric cellulite severity scale (17.0%) and patient-reported photonumeric cellulite severity scale (25.7%) (p < 0.001). The overall quality of the studies using the grading of recommendations, assessment, development and evaluation approach was moderate. This is the first methodologically robust systematic review evaluating interventions for cellulite. SWT, radiofrequency therapy, and subcutaneous injectables have shown promising findings in cellulite treatment. The journal asks authors to assign a level of evidence to each article. For a complete description of Evidence-Based Medicine ratings, see the Table of Contents or the online Instructions for Authors at www.springer.com/00266 .

WEAVE First Light Observations: Origin and Dynamics of the Shock Front in Stephan’s Quintet

WEAVE First Light Observations: Origin and Dynamics of the Shock Front in Stephan’s Quintet

Effects of the inflow total temperature on the non-premixed rotating detonation engine performances

As a promising propulsion system, air-breathing rotating detonation engines (RDEs) are investigated with significant interest recently. However, simulations of air-breathing RDE with real flight condition are limited, and performance of RDEs with high inflow total temperature, as well as the influence of inflow total temperature on RDEs, needs further exploration. In this paper, simulations with four inflow total temperatures (300 K, 500 K, 700 K and 900 K) were conducted to analyze the propagation features of rotating detonation waves (RDWs) and operation modes in the RDE at low and high inflow total temperatures. Additionally, injection and mixing, as well as combustion characteristics and propulsion performance of the RDE were researched. It is found that with low inflow total temperature, single wave propagates in the combustor, which degenerates into shock wave at the outer wall due to insufficient mixing. When inflow total temperature is high, the RDE is in multi-wave operation mode and detonative combustion only occurs around the outer wall. With increase of inflow total temperature, mixability of reactants initially improves but then deteriorates slightly. Moreover, RDW propagation velocity and specific impulse of the RDE decrease. Though fuel utilization rate improves, detonation fraction drops dramatically and parasitic combustion fraction rises significantly, resulting from intensification of pre-combustion. Particularly, the detonation fraction is only 16.7 % and parasitic combustion fraction reaches up to 56.35 % at inflow total temperature of 900 K. Furthermore, regardless of the variation of inflow total temperature, detonative combustion is prominent in the premixed combustion mode, and the peak fraction of detonation appears at the off-stoichiometric ratio.

Numerical Investigation of Network-Based Shock Wave Propagation of Designated Methane Explosion Source in Subsurface Mine Ventilation System Using 1D FDM Code

In coal mining operations, methane explosions constitute a severe safety risk, endangering miners’ lives and causing substantial economic losses, which, in turn, weaken the production efficiency and economic benefits of the mining industry and hinder the sustainable development of the industry. To address this challenge, this article explores the application of decoupling network-based methods in methane explosion simulation, aiming to optimize underground mine ventilation system design through scientific means and enhance safety protection for miners. We used the one-dimensional finite difference method (FDM) software Flowmaster to simulate the propagation process of shock waves from a gas explosion source in complex underground tunnel networks, covering a wide range of scenarios from laboratory-scale parallel network samples to full-scale experimental mine settings. During the simulation, we traced the pressure loss in the propagation of the shock wave in detail, taking into account the effects of pipeline friction, shock losses caused by bends and obstacles, T-joint branching connections, and cross-sectional changes. The results of these two case studies were presented, leading to the following insights: (1) geometric variations within airway networks exert a relatively minor influence on overpressure; (2) the positioning of the vent positively contributes to attenuation effects; (3) rarefaction waves propagate over greater distances than compression waves; and (4) oscillatory phenomena were detected in the conduits connecting to the surface. This research introduces a computationally efficient method for predicting methane explosions in complex underground ventilation networks, offering reasonable engineering accuracy. These research results provide valuable references for the safe design of underground mine ventilation systems, which can help to create a safer and more efficient mining environment and effectively protect the lives of miners.