Shock Waves最新文献

Rotating detonation propulsion technologies have the potential to create highly efficient engines in a small form factor. However, the detonation dynamics and complex flowfields inside the combustion chamber are greatly dependent on geometry; in particular, the downstream nozzle design affects dynamics inside the combustion chamber. In this work, three-dimensional large eddy simulations of a gaseous methane–oxygen rotating detonation rocket engine are presented for two geometries. The geometries match experimental tests previously conducted at the Air Force Research Laboratory and are chosen to compare engine operation with and without a converging–diverging nozzle. It is shown that flow in the unconstricted chamber exceeds Mach 1 behind the generated oblique shock structure, but that the addition of a 4.4(^circ ) converging section results in supersonic flow existing only in the diverging section of the nozzle. The formation enthalpy of the flow is calculated inside the chamber and demonstrates that the difference in pressures and detonation structures associated with the chamber area constriction do not result in a significant change in energy released through combustion.

The effects of ozone addition and low-temperature chemistry (LTC) progression on DME/O(_{2}) detonations are evaluated with experimental detonation velocity and cell size measurements and one-dimensional ZND simulations. For ( phi = 1.2) and (P_{textrm{o}}= 22.7) kPa, detonations are experimentally investigated over a range of ozone enhancement levels (0.0–1.6-mol%), initial reactant temperatures (293 K and 468 K), and LTC progression times (250–6000 ms). A 33-K gas temperature rise from LTC heat release is observed for mixtures with 1.0-mol% ozone enhancement and initial temperature of 468 K, suggesting a limited extent of LTC progression in this study. Experiments showed minimal detonation velocity dependence on ozone enhancement level or LTC progression despite the increased radical pool. Average cell size is found to decrease 15–30% with 1.6-mol% ozone addition, indicating a greater reactant mixture sensitivity to detonation. To estimate the cell size, a center-of-exothermic-length induction length is defined and used with an empirical correlation to calculate a singular cell size when multiple thermicity peaks are present in ZND modeling. This approach shows good agreement with experimental findings. Cell size dependence on LTC progression is found to have a statistically insignificant variance for LTC progression times at the temperatures used in this study.

The interaction and coalescence of shock waves originating from multiple explosion sources were studied using numerical simulations and theoretical analysis. The effects of the mass distribution, layout, and quantity of explosion sources were considered, and an engineering calculation model for shock wave parameters at the focus center was established. The results show that the peak overpressure at the focus center is significantly changed only when the mass ratio of the two explosion sources increases beyond two. Overall, the peak overpressure at the focus center decreases with the increase in mass ratio. The focus effect of multiple explosion sources is the greatest when the sources are uniformly distributed on a circle. When the number of explosion sources is less than four, the peak overpressure and specific impulse at the focus center increase with the increase of the number of explosion sources. Increasing the number of explosion sources from one to four results in an increase in the peak overpressure by a factor of 0.73–5.23 and an increase in the specific impulse gain by a factor of 1.59–4.71. The results from simulations and experiments verify the validity of the model used to characterize multiple explosion sources.

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.

The 2020 Beirut port’s ammonium nitrate explosion led to the most severe damage, in terms of human lives and property loss, ever seen in the history of Beirut, the capital of Lebanon. The current study focuses on the blast damage of tall buildings near the explosion site and analyses the overpressure/distance relationship based on the comparison between theoretical calculations, the blast damage scale from the SFPE Handbook of Fire Protection Engineering, and real post-explosion images. The estimated trinitrotoluene equivalent blast size for the research is assumed to be 713 tons. Six tall buildings at different distances were included in the research and divided into categories. Theoretical overpressure models of Baker’s, Sadovski’s, and Alonso’s methods and Blast Operational Overpressure Model were used in combination with the Kingery–Bulmash Blast Parameter online calculator. A wide range of overpressure values were observed. The calculated values from the theoretical overpressure models were incorporated into the blast damage scale and compared with the real images, with the better match being mainly demonstrated for buildings at closer distances.

The imperfection of shock-reloading experiments has become the main obstacle to measuring the dynamic yield strength of materials under shock compression within the framework of the self-consistent strength-measuring method. In this work, we report an improved shock-reloading technique, in which additional layers of high-hardness materials are used as the backing of the two-layer impactor to eliminate the impactor’s distortion and thus overcome the long-standing debonding issue during launching. This technique has the merits of easy accessibility, no modification of material properties, and being applicable to any materials, therefore providing a practicable and reliable way to obtain high-quality reloading data. As a demonstration, we adopt this technique to shock-reloading experiments in aluminum up to 71 GPa and record high-quality particle-velocity profiles with the details of the quasi-elastic reloading from the initial shocked state. The dynamic yield strengths are then determined using the self-consistent method and found to be consistent with data available in the literature.

In recent years, several studies have been dedicated to modeling of detonations including assumptions of thermal non-equilibrium. Modeling using two-temperature models has shown that non-equilibrium affects detonation dynamics. However, the deployment of state-to-state models, one of the foremost non-equilibrium modeling tools, in detonation modeling remains under-explored. In this work, we detail the implementation of a STS model of ({hbox {N}_{2}}) and ({hbox {O}_{2}}) in a Zel’dovich–von Neumann–Döring reactor for a mixture of ({hbox {H}_{2}})–air. Certain modifications to the usual theory and models must be performed before the deployment of aforementioned model, namely in the thermodynamics formulation. Additionally, since most codes are not compatible with STS models, a validation of an in-house code is carried out against CHEMKIN. Results indicate that the multi-temperature approach adopted in earlier works is likely not appropriate to model the internal distribution function of ({hbox {O}_{2}}) and therefore should be used with caution. A comparison of an estimated cell width with experimental values confirms the potential of the STS framework for a more accurate detonation modeling.

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-(upmu )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.