Shock Waves最新文献

The effect of heat and momentum losses on the steady solutions admitted by the reactive Euler equations with sink/source terms is examined for stoichiometric hydrogen–oxygen mixtures. Varying degrees of nitrogen and argon dilution are considered in order to access a wide range of effective activation energies, (E_{textrm{a,eff}}/R_{textrm{u}}T_{0}), when using detailed thermochemistry. The main results of the study are discussed via detonation velocity-friction coefficient (D–(c_{textrm{f}})) curves. The influence of the mixture composition is assessed, and classical scaling for the prediction of the velocity deficits, (D(c_{textrm{f,crit}})/D_{textrm{CJ}}), as a function of the effective activation energy, ({E}_{textrm{a,eff}}/R_{textrm{u}} T_{0}), is revisited. Notably, a map outlining the regions where set-valued solutions exist in the (E_{textrm{a,eff}}/R_{textrm{u}}T_{0}text {--}{alpha }) space is provided, with (alpha ) denoting the momentum–heat loss similarity factor, a free parameter in the current study.

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.

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.

Blast-induced traumatic brain injury has long been a prevalent health issue. There is growing concern for repeated exposures to low-level blasts with studies suggesting effects on neurological impairments and long-term health problems. The purpose of this study was to expand our understanding of the neurophysiological consequences of repetitive mild blast from a range of occupational exposure levels. We studied shock waves of peak overpressures ranging from 45 to 270 kPa and impulses of 54 to 295 kPa(cdot )ms. We observed the effects of these shock waves in organotypic hippocampal slice cultures generated from neonatal rat pups. This model allowed us to isolate the effects of blast on neuronal function without the confounding factors of scaling and peripheral systemic input. We found that blast severity and inter-blast interval were both integral in understanding non-injurious limits for blast exposure. With higher blast severity, the inter-blast interval needed to be extended to avoid deficits in long-term potentiation (LTP), a form of synaptic plasticity. Furthermore, blast exposures too close in time synergistically affected LTP negatively, producing a dose response with more exposures leading to greater deficits in LTP. Overall, even the lowest blast tested was capable of producing functional deficits under the appropriate conditions. These findings can aid in the improvement of safety and training protocols to set occupational exposure limits to avoid neurological impairments and negative long-term health effects.

The transition between Mach reflection (MR) and regular reflection (RR) of gaseous detonations in argon-diluted stoichiometric hydrogen–oxygen was investigated experimentally using a wedge with a concave–convex surface. The continuous MR triple-point trajectory was recorded using the smoked foil technique, from which the transition angles for ({textrm{MR}}leftrightarrow {textrm{RR}}) transitions could be determined. Similar to the reflection of a non-reacting shock wave, the non-stationary hysteresis phenomenon was found for detonation reflection, i.e., the ({textrm{MR}}rightarrow {textrm{RR}}) transition angle was much larger than that for ({textrm{RR}} rightarrow {textrm{MR}}) transition. In addition, the ({textrm{RR}} rightarrow {textrm{MR}}) transition angle on the convex surface was smaller than that for detonation reflection over a single half-cylinder. This is opposite to what is found for non-reacting shock wave reflection.

Brain injuries in warfighters due to low-level blasts, even while wearing a helmet, are common. Understanding how the form of a shock wave changes when impacting a head donning a helmet may present solutions to reducing shock loading on the head, thereby reducing the prevalence of blast-induced traumatic brain injury. A manikin with PCB piezoelectric transducers throughout the head was exposed to low-pressure free-field blasts using an RDX-based explosive charge designed to output a side-on overpressure of 4 pounds per square inch (psi) [27.5 kilopascals (kPa)] with and without a helmet. Orientations of 0, 45, 90, 135, and 180 degrees were evaluated to observe changes in overpressure versus time (p(t)) waveforms. The waveforms were compared to schlieren imagery in which a shock wave impacted 3D-printed silhouettes of a warfighter donning a helmet, showing shock wave flow under the helmet at 0-, 90-, and 180-degree orientations. It was found that trapped shock waves under the helmet create regions of high overpressure and increase the duration of exposure, resulting in higher impulses imparted onto the head. While wearing a helmet, the 90-degree orientation resulted in the greatest reduction in overall peak overpressure, with an 8% decrease compared to the 0-degree orientation. In contrast, the 180-degree orientation led to an increase by 30%. For impulse, the 90-degree orientation showed the greatest reduction, with a decrease of 21%. The 0-degree orientation had the highest overall impulse among all orientations when wearing a helmet.