Shock Waves最新文献

A rotating detonation engine (RDE) is expected to achieve a pressure gain (PG) in which the total pressure of the product at the engine exit exceeds the total pressure of the supplied oxidizer. However, many non-ideal phenomena exist in the RDE, which hinder the achievement of a PG. This study focused on the channel expansion angle near injector outlet which is considered to impact the structure of detonation wave and the PG performance. Combustion tests were conducted by varying the channel expansion angle near the axially injected oxidizer injector outlet to 90(^{circ }) and 30(^{circ }). As a result, the thrust was not affected by the expansion angle, but the propagation velocity of detonation wave at an expansion angle of 90(^{circ }) was approximately 5% higher than that at an expansion angle of 30(^{circ }). A comparison utilizing the pressure increase ratio obtained from the fluctuating pressure in the combustion chamber suggested that the Mach number of the detonation wave was higher for an expansion angle of 90(^{circ }). As a result of evaluating the PG performance utilizing the equivalent available pressure obtained from thrust measurements, it was not confirmed to differ with changes in the expansion angle.

The unwarranted leakage/release of hydrogen gas from metal processing, automotive, petrochemical industries, and nuclear reactors, along with its subsequent ignition and transition to detonation, could lead to catastrophic damage to both life and property. The development of practical hazard prevention and safety control systems demands an understanding of the effectiveness of the chemical inhibitors to suppress/mitigate a detonation wave under varying operational conditions. In the current study, the inhibition efficiency of chemical inhibitors under varying mixture initial conditions was investigated using numerical computations. The inhibition efficiency of trifluoroiodomethane (CF(_{textrm{3}})I), carbon dioxide (CO(_{textrm{2}})), and steam (H(_{textrm{2}})O) on hydrogen-oxygen/air mixtures was evaluated using a detailed chemical kinetic model for hydrogen oxidation. ZND computations were carried out over a range of initial mixture composition, pressure, and temperature. It was found that CF(_{textrm{3}})I is a better inhibitor than CO(_{textrm{2}}) and H(_{textrm{2}})O at all the initial mixture conditions. However, at very high temperatures, the inhibitors CF(_{textrm{3}})I, CO(_{textrm{2}}), and H(_{textrm{2}})O have a similar detonation inhibition efficiency. The inhibition efficiency of carbon dioxide and steam is comparable and significantly lower than CF(_{textrm{3}})I. The findings from the current work can be used to design optimized detonation safety systems over a range of practical operating conditions.

The current study numerically evaluates the detonation inhibition effects of a range of halogenated compounds on hydrogen-air gaseous detonations. The halogenated compounds investigated in this research encompass halogen acids (HI, HBr, HCl, HF), halomethanes ((hbox {CH}_{{3}}hbox {I}), (hbox {CH}_{{3}}hbox {Br}), (hbox {CH}_{{3}}hbox {Cl}), (hbox {CH}_{{3}}hbox {F})), haloethenes ((hbox {C}_{{2}}hbox {H}_{{3}}hbox {I}), (hbox {C}_{{2}}hbox {H}_{{3}}hbox {Br}), (hbox {C}_{{2}}hbox {H}_{{3}}hbox {Cl}), (hbox {C}_{{2}}hbox {H}_{{3}}hbox {F})), haloethanes ((hbox {C}_{{2}}hbox {H}_{{5}}hbox {I}), (hbox {C}_{{2}}hbox {H}_{{5}}hbox {Br}), (hbox {C}_{{2}}hbox {H}_{{5}}hbox {Cl}), (hbox {C}_{{2}}hbox {H}_{{5}}hbox {F})), and complex halogenated compounds ((hbox {CF}_{{3}}hbox {I}), (hbox {CF}_{{3}}hbox {Br}), (hbox {CF}_{{3}}hbox {Cl}), (hbox {CF}_{4})). The study employs a one-dimensional ZND model with detailed chemical kinetics to examine the impact on detonation propagation by adding these halogenated compounds to hydrogen-air mixtures. The effectiveness of these inhibitors is evaluated based on their capacity to increase the induction length, the amount of inhibitor needed to attenuate a detonation wave, and their influence on the detonability of the gaseous mixture under both lean and rich conditions. The results indicate that several halogenated compounds exhibit superior inhibition properties compared to Halon 1301 ((hbox {CF}_{{3}}hbox {Br})). Specifically, (hbox {C}_{{2}}hbox {H}_{{5}}hbox {Br}) leads to the most significant increase in the induction length, with HBr and (hbox {C}_{{2}}hbox {H}_{{5}}hbox {I}) following closely, particularly at 20,000 ppmv concentration levels. However, it is worth noting that the inhibition efficiency also varies depending on the concentration of the inhibitor added to the gaseous (hbox {H}_{{2}})-air mixture. Moreover, based on retardant weight analysis, fluorinated compounds were found to be the most effective inhibitors, followed by chlorinated, brominated, and iodinated compounds across all categories of halogenated inhibitors.

Characteristic timescales for rotating detonation rocket engines (RDREs) are described in this study. Traveling detonations within RDREs create a complex reacting flow field involving processes spanning a range of timescales. Specifically, characteristic times associated with combustion kinetics (detonation and deflagration), injection (e.g., flow recovery), flow (e.g., mixture residence time), and acoustic modes are quantified using first-principle analyses to characterize the RDRE-relevant physics. Three fuels are investigated including methane, hydrogen, and rocket-grade kerosene RP-2 for equivalence ratios from 0.25 to 3 and chamber pressures from 0.51 to 10.13 MPa, as well as for a case study with a standard RDRE geometry. Detonation chemical timescales range from 0.05 to 1000 ns for the induction and reaction times; detonation-based chemical equilibrium, however, spans a larger range from approximately 0.5 to (200~upmu )s for the flow condition and fuel. This timescale sensitivity has implications regarding maximizing detonative heat release, especially with pre-detonation deflagration in real systems. Representative synthetic detonation wave profiles are input into a simplified injector model that describes the periodic choking/unchoking process and shows that injection timescales typically range from 5 to (50~upmu )s depending on injector stiffness; for detonations and low-stiffness injectors, target reactant flow rates may not recover prior to the next wave arrival, preventing uniform mixing. This partially explains the detonation velocity deficit observed in RDREs, as with the standard RDRE analyzed in this study. Finally, timescales tied to chamber geometry including residence time are on the order of 100–10,000 (upmu )s and acoustic resonance times are 10–(1000~upmu )s. Overall, this work establishes characteristic time and length scales for the relevant physics, a valuable step in developing tools to optimize future RDRE designs.

Evidence suggests that low-level blast (LLB) overpressure exposure from military heavy weapons training is associated with subclinical adverse brain health and performance (H &P) outcomes. Existing DOD safety policies related to blast overpressure exposure are not specific to LLB-related brain health effects. This study sought to synthesize the available literature and analyze the relevancy of a specific blast metric to LLB exposures and the manifestation of adverse brain H &P outcomes. A literature search yielded 311 unique articles, from which 220 were identified as human studies on LLB published from 2010 to 2021. After more exhaustive exclusion criteria were applied, 14 articles met the criteria for inclusion. Findings on brain H &P changes were examined in relation to quantified LLB measurements (e.g., peak overpressure) to identify trends. Overall, the included studies suggested that alterations of reaction time, a metric for neurocognitive performance, as well as symptom reporting can occur following cumulative LLB exposures above 4 psi (27.6 kPa). Biomarkers and neurosensory changes have not demonstrated consistent associations with LLB exposures. These findings suggest that cumulative blast overpressure exposures above 4 psi (27.6 kPa) based on current measurement methodologies for body-worn sensors may be associated with adverse brain H &P outcomes. Current research efforts seek to better quantify LLB exposure, the relationships between LLB (e.g., intensity, duration, dose) and brain health, as well as to assess brain H &P domains more comprehensively. These efforts will serve to promote a better understanding of the interaction between LLB exposures and adverse brain H &P outcomes.

The neurological consequences of combat blast-induced neurotrauma (BINT) pose important clinical concerns for military service members and veterans. Previous studies have shown that low-intensity blast (LIB) results in BINT with multifaceted characteristics in mice exposed to open-field blast in prone position. Although the prone position is natural for rodents, experimental models of blast using this position do not represent common scenarios of human standing while being exposed to blast during deployment or military training. In this study, we used our previously developed BINT mouse model of open-field LIB with mice in an upright position and then used quantitative proteomics and multiple bioinformatic approaches to analyze brain tissue taken from multiple subregions during the acute post-injury phase. We identified: (1) region-specific BINT-induced proteome changes, which were significantly and differently influenced by animal positioning (upright vs. prone): the upright positioning caused more significant protein alterations in cortex and cerebellum, which were less significant in striatum as compared to prone position; (2) synapse- and mitochondrion-related damage contributed to BINT in both positions; and (3) some molecular signatures were exclusively and/or oppositely regulated in two positions. This study delineates the molecular signatures of the position-dependent blast effects, indicating the importance of brain–body position for BINT translational studies and for modeling the location and extent of position-related blast injuries.

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.

This note presents a vapor-based seeding apparatus, named the external alkali seeding instrument (EASI), which is designed to introduce alkali metal vapors into experimental facilities without using precursors or large auxiliary equipment. The device vaporizes small amounts of alkali metals, potassium in this work, which are then carried away by an inert gas. In a benchtop flow cell, carrier gas flow rate (6–(200~hbox {cm}^3/hbox {s})) and device temperature (150–(250,^{circ }hbox {C})) most strongly affected potassium-vapor concentrations. Higher values of either quantity lead to increased potassium-vapor concentrations. When using the EASI to seed a shock tube experiment, vapor-phase potassium was detected immediately after the incident and reflected shockwaves using a laser absorption diagnostic. Mole fraction time histories stay within a factor of 2 over the test time as compared with those from a precursor-based seeding approach, which may span multiple orders of magnitude. This suggests potassium is nearly homogeneously distributed throughout the test gas. This design can be extended to other low-vapor-pressure elements, such as other alkalis or sulfur, with minimal modifications. The EASI simplifies seeding for laboratory experiments targeting potassium and other alkali metals—enabling advances in fundamental spectroscopy, diagnostic development, and chemical kinetics.

An experimental investigation was carried out to study the fluid–structure interactions on a compliant panel subjected to an impinging shock wave and an incoming turbulent boundary layer. These experiments were aimed at understanding the time-averaged and unsteady characteristics of fluid–structure interaction at Mach 2. Two shock impingement locations on the panel (aspect ratio of 2.82), namely the central and three-fourths of the panel length, were tested. The shock boundary layer interactions on a rigid flat plate served as a baseline case. Measurements include shadowgraph and surface oil flow visualizations, panel deflections using a capacitance probe, cavity acoustics using a pressure sensor, surface pressures using discrete pressure sensors, and pressure-sensitive paints. Results show that the interaction on the compliant panel is relatively three-dimensional as compared to a rigid plate with a nominally two-dimensional interaction. Pressure fluctuations on the compliant panel are significantly higher than on the rigid plate, and the fluctuation spectra are multi-modal. Strong coupling at some frequencies was observed between the shock and the panel for both shock impingement locations. The present study suggests that for a compliant panel, the shape of pressure spectra is sensitive to the measurement location on the panel, the panel modifies the pressure distribution around the interaction, and the energy in dominant modes depends on the shock impingement location.