Shock Waves最新文献

Contrary to the conventional chemical propulsion systems based on the controlled relatively slow (subsonic) combustion of fuel in a combustor, the operation process in pulsed detonation engines (PDEs) and rotating detonation engines (RDEs) is based on the controlled fast (supersonic) combustion of fuel in pulsed and continuous detonation waves, respectively. One of the most important issues for such propulsion systems is the choice of fuel with proper reactivity and exothermicity required for a sustained and energy-efficient operation process. Presented in the paper are the results of thermodynamic calculations of the detonation parameters of boron- and aluminum-containing compounds (B, B(_{{2}})H(_{{6}}), B(_{{5}})H(_{{9}}), B(_{{10}})H(_{{14}}), Al, AlH(_{{3}}), Al(C(_{{2}})H(_{{5}})_{{3}}), and Al(CH(_{{3}})_{{3}})) in air and water. The results demonstrate the potential feasibility of using the considered compounds as fuels for both air- and water-breathing transportation vehicles powered with PDEs and RDEs. As a verification of the reliability of the calculated results, the detonation parameters of diborane, aluminum, and isopropyl nitrate in air were compared with experimental data available in the literature.

A study of shock and detonation waves propagating in gaseous two-fuel (hbox {CH}_{{4}}/hbox {H}_{{2}})/air mixtures and heterogeneous three-fuel (hbox {CH}_{{4}}/hbox {H}_{{2}})/air/coal mixtures with the mean bulk density of the coal dust suspension equal to (95{-}560,hbox {g/m}^{{3}}) and with a particle size of (0{-}200,upmu hbox {m}) is performed. The experiments are conducted in a vertical shock tube with a length of 6.75 m and a diameter of 70 mm. The detonation parameters measured in the experiments are compared with the calculated equilibrium thermodynamic values. It is found that the detonation wave parameters are mainly affected by methane and hydrogen rather than by the coal dust suspension. Decaying shock waves are as dangerous as detonation waves because blast wave reflections can initiate detonation. An increase in the hydrogen fraction in the mixture decreases the energy of initiation of (hbox {CH}_{{4}}/hbox {H}_{{2}})/air and (hbox {CH}_{{4}}/hbox {H}_{{2}})/air/coal mixtures, resulting in a greater hazard for the generation of shock and detonation waves in these mixtures.

Explosively driven shock wave radius versus time profiles are frequently used to document energy release and relative explosive performance. Recently, two universal shock wave radius versus time profiles have been presented in the literature, which demonstrate the ability to represent explosively driven shock wave profiles for all explosive sources in any fluid environment. These two universal shock wave profiles are examined here relative to each other and relative to a commonly used nonlinear shock wave profile, which is fit to experimental data for individual explosive materials. The nonlinear profile, originally developed by Dewey, is examined here, and a universal non-dimensional form of the equation is proposed. The universal shock wave profiles are all found to be relatively similar, but with slight variations in a transition region of non-dimensional radii (0.15lesssim R^*lesssim 2). The variations in this region result in different estimations of energy release or blast strength between the curve fits.

The present work is a numerical follow-up on our published experimental paper on shock ignition of aluminium particle clouds in the low-temperature regime. The in-house multi-phase regularized smoothed particle hydrodynamics (MP-RSPH) code is used to perform numerical simulations with an increasing degree of complexity, looking at single-phase, inert, and reactive particles in separate simulations. The first part of the paper gives a short description of the additional physics added to the code. Based on the experimental results, the numerical code is then used to estimate the particle temperature at the time of ignition. Results from simulations with three different numerical descriptions, the diffusive, kinetic, and total burn rates, are then compared to the experimental results. The two diffusive burn rate simulations (K &H and O &H) show the best fit to the experimental results. The burn rate formula based on our experimental data (O &H) is preferred, since it has the gas temperature dependency included and does not require additional parameter adjustments. The results from the numerical simulations support the theory that the observed aluminium particle cloud burning process is diffusive, as indicated in the experimental paper.

The inerting of a detonable mixture through thermal pretreatment or parasitic combustion is critical to understand for advanced detonation-based combustor design and safety. This work addresses the inerting effects of low temperature chemistry (LTC) on detonations. LTC was induced in both ozoneless DME/O(_{textrm{2}}) and 1.0 mol% O(_{{3}})-enhanced DME/O(_{2}) mixtures over a range of detonation tube temperatures ((T_{textrm{o}})) from 423 to 648 K for reactant mixture equivalence ratios ((phi )) of 0.6–1.8. Upon filling the detonation tube, reactant gas temperatures increased by over 100 K in some cases but never exceeded a maximum gas temperature of 700 K, suggesting a limiting behavior such as the RO(_{2}) ceiling temperature. Zero-dimensional constant-volume simulations were conducted to identify chemical composition changes and heat releasing reactions with LTC pretreatment, and ZND simulations were conducted to show the evolution of thermicity with LTC pretreatment. Prolonged pretreatment at (T_{textrm{o}}) greater than 573 K prior to spark ignition of detonation was observed to inert DME/O(_{2}) mixtures and inhibit detonation transition for all tested (phi ). Additionally, detonation cell sizes were measured, and increased DDT distances and detonation cellular instability at near-limit conditions due to LTC pretreatments were observed using soot foils. Numerical cell sizes were estimated using a correlation model based on center-of-exothermic-length from ZND thermicity simulations, and results showed good agreement with experimental cell sizes. Stability parameter and DDT distance analyses based on correlation models supported the observed reduction in mixture detonability and increase in DDT distances with LTC pretreatment progression.

The present work is focused on the numerical analysis of the flow structures of high-speed underwater air jets. In an earlier work (Jana et al., J. Fluids Eng. 144(11):111208, 2022), the authors presented an analysis of the unsteady behavior of different flow variables of the jets. The present work is further extended to analyze the temporal evolution of the flow structures of different jet regions. The numerical simulations are conducted with the unsteady Reynolds-averaged Navier–Stokes equations with a homogeneous mixture model. The previous work rendered the effect of pressure ratio (the ratio of nozzle exit pressure to back pressure) on the behavior of the jet flow. In the present analysis, jet exit Mach number is also considered as another operating parameter. The results for three pressure ratios, 0.8, 1, and 1.2, and two exit Mach numbers, 2 and 3, are presented. Temporal behavior of the three major regions, namely, the core, shear layer, and mixing layer of the jet due to its interaction with surrounding water, is discussed. The flow physics of shock and expansion waves in the core region is analyzed, and the effects of the underwater ambience on the structures of shock waves are also explained. Various phenomena, such as necking, back-attack, and expansion, are also visualized and explained from the simulated flow variables. Given the limitations of experimental flow visualizations, these analyses aid to understand the major flow behavior of supersonic underwater jets.

Aerobreakup of fluid droplets under the influence of impulsively generated high-speed gas flow using an open-ended shock tube is studied using experiments and numerical simulations. Breakup of millimeter-sized droplets at high Weber numbers was analyzed for water and two-phase nanofluids consisting of dispersions of ({{hbox {Al}}_{2}{hbox {O}}_{3}}) and ({{hbox {TiO}}_{2}}) nanoparticles in water with high loading of 20 and 40 wt%, respectively. Droplet breakup is visualized using high-speed imaging in the experimental setup, where an open-ended shock tube generates impulsive high-speed flow impinging on a droplet held stationary using an acoustic levitator. Axisymmetric simulations using the volume-of-fluid technique are conducted to capture the gas dynamics of the flowfield and droplet deformation at the initial stages. Fluid droplets are subject to a transient flowfield generated by the open-ended shock tube, characterized by a propagating incident shock wave, a recirculating vortex ring, and standing shock cells. Droplet breakup for all fluids proceeds through an initial flattening of the droplet followed by generation of a liquid sheet at the periphery in the presence of a curved detached shock front at the leading edge. The breakup appears to follow a sheet stripping process whereby stretched ligaments undergo secondary atomization through viscous shear. Mist generated in the wake of the droplet appears to expand laterally due to the unconstrained expansion of the high-speed gas jet. The breakup morphology of droplets for all fluids appears consistent with previous observations using conventional shock tubes. Lateral deformation of the coherent droplet mass is observed to be higher for nanofluids as compared to water. This is attributed to higher viscosity and Ohnesorge number of nanofluid droplets, which results in delayed breakup and increased lateral stretching. When plotted as a function of non-dimensionalized time, the same effects are also attributed to generate the highest non-dimensional velocities for the ({{hbox {TiO}}_{2}}) nanofluid, followed by ({{hbox {Al}}_{2}{hbox {O}}_{3}}) nanofluid, and water, which mirrors the order of viscosity and Ohnesorge number for the three fluids. An area of spread, which can be interpreted as a measure of dispersion, plotted as a function of non-dimensionalized time also shows the highest value for the ({{hbox {TiO}}_{2}}) nanofluid, followed by ({{hbox {Al}}_{2}{hbox {O}}_{3}}) nanofluid, and water. Overall, current results indicate that droplet breakup for two-phase fluids appears to be similar to those for single-phase fluids with effectively higher viscosity. Furthermore, an open-ended shock tube proves to be an effective tool to study droplet aerobreakup, with some differences observed in the droplet wake due to the unconfined expansion of gas flow.

The paper describes the dual behavior observed for hydrogen peroxide when added to hydrogen-air detonating mixtures. The effect of the addition of hydrogen peroxide on (text {NO}_{x}) emissions and critical detonation parameters was evaluated for (text {H}_{2}) air mixtures using one-dimensional ZND calculations. Hydrogen peroxide acts as an ignition promoter and is shown to significantly enhance the detonation chemistry when added in small concentrations. It alters the ignition chemistry of an underlying detonation wave without affecting the bulk thermodynamic properties. The main objective of the present study is to evaluate the ignition promotion and (text {NO}_{x}) mitigation effects of hydrogen peroxide in gaseous detonations when it is added to hydrogen-air mixtures in small and large concentrations. In the current work, the diminishing sensitizing potential of hydrogen peroxide when added in large amounts (up to 10%) is also reported. The results show a visible effect on ignition promotion up to 20,000 ppm. At concentrations higher than 20,000 ppm of (text {H}_{2}text {O}_{2}), further reduction in the induction length was found to be minimal. The (text {NO}_{x}) emissions were found to decrease for stoichiometric and fuel-lean (text {H}_{2})-air mixtures, whereas the (text {NO}_{x}) concentration was found to increase for fuel-rich mixtures with the addition of hydrogen peroxide. Thus, the dual behavior exhibited by (text {H}_{2}text {O}_{2}) is shown to be advantageous as it could potentially mitigate (text {NO}_{x}) emissions at high temperatures for fuel-lean and stoichiometric hydrogen-air mixtures and, at the same time, could sensitize the given mixture for applications in detonation-based combustors.

A multicomponent force balance was designed to measure the drag and rolling moment using an accelerometer-based technique. The force balance system used a linear ball bush as a new model mount system to minimize the constraint of the test model motion in both the axial and rotational directions. The accelerations of the test model were measured in the axial and rotational directions using accelerometers that were externally mounted on the test model. The drag and rolling moment were recovered from the measured accelerations using the system response functions, which included the dynamic characteristics of the force balance system. The system response functions were determined from the force balance calibration processes by applying a series of point loads in the axial and rotational directions and deconvolving the resulting accelerations. The drag and rolling moment measurements on the wedge model, including the flaps, were performed in a shock tunnel with a test time of approximately 3 ms at a nominal freestream Mach number of 6. A computational fluid dynamics (CFD) analysis assuming a laminar boundary layer was performed. Good agreement was obtained between the measured and calculated results. An uncertainty analysis of the measurements was conducted with regard to the influence of the fundamental properties of the test condition and force balance system.

Experimental results on the interactions between a single water droplet and a shock wave propagating at Mach number above 4 are presented in this paper. A detonation-driven shock-tube test facility is used to work within a Mach range at ({M}=4.3) (high-supersonic regime) and ({M}=10.6) (hypersonic regime), for which the maximum studied dimensionless times T are up to 9.4 and 5.5, respectively. For both Mach ranges, the initial droplet diameters typically vary between 430 and 860 (upmu hbox {m}) and the associated Weber numbers vary from (5 times 10^{4}) to (11 times 10^{4}). Ultra-high-speed cameras are used to record the evolution of the water droplet when the shock wave impacts it. Until ({T} approx 2.5), the qualitative and quantitative analyses of our frames show that the initial diameter as well as the Mach number studied have an apparent weak influence on the droplet dimensionless displacement. Beyond this time, the results for ({M}=10.6) are more dispersed than the data for ({M}=4.3) revealing a possible effect of the droplet size. One of the main results of this paper is that the droplet disappearance occurs at ({T}=[4.5)–5.5] for ({M}=10.6), while some mist is still present at ({T}>9) for ({M}=4.3). We note also that the droplet is always supersonic for ({M}=10.6) whereas it becomes subsonic at ({T}approx 3.5) for ({M}=4.3).