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Showing papers on "Shock wave published in 2017"


Journal ArticleDOI
TL;DR: In this paper, the cosmic ray (CR) evolution equations coupled to magneto-hydrodynamics (MHD) on an unstructured moving mesh, as realised in the massively parallel AREPO code for cosmological simulations, are discussed.
Abstract: We discuss new methods to integrate the cosmic ray (CR) evolution equations coupled to magneto-hydrodynamics (MHD) on an unstructured moving mesh, as realised in the massively parallel AREPO code for cosmological simulations. We account for diffusive shock acceleration of CRs at resolved shocks and at supernova remnants in the interstellar medium (ISM), and follow the advective CR transport within the magnetised plasma, as well as anisotropic diffusive transport of CRs along the local magnetic field. CR losses are included in terms of Coulomb and hadronic interactions with the thermal plasma. We demonstrate the accuracy of our formalism for CR acceleration at shocks through simulations of plane-parallel shock tubes that are compared to newly derived exact solutions of the Riemann shock tube problem with CR acceleration. We find that the increased compressibility of the post-shock plasma due to the produced CRs decreases the shock speed. However, CR acceleration at spherically expanding blast waves does not significantly break the self-similarity of the Sedov-Taylor solution; the resulting modifications can be approximated by a suitably adjusted, but constant adiabatic index. In first applications of the new CR formalism to simulations of isolated galaxies and cosmic structure formation, we find that CRs add an important pressure component to the ISM that increases the vertical scale height of disk galaxies, and thus reduces the star formation rate. Strong external structure formation shocks inject CRs into the gas, but the relative pressure of this component decreases towards halo centres as adiabatic compression favours the thermal over the CR pressure.

161 citations


Journal ArticleDOI
TL;DR: In this paper, the low-frequency dynamics of a high Reynolds number impinging shock-wave/turbulent boundary-layer interaction with strong mean-flow separation were analyzed for grid-converged large-eddy simulations.
Abstract: We analyse the low-frequency dynamics of a high Reynolds number impinging shock-wave/turbulent boundary-layer interaction (SWBLI) with strong mean-flow separation. The flow configuration for our grid-converged large-eddy simulations (LES) reproduces recent experiments for the interaction of a Mach 3 turbulent boundary layer with an impinging shock that nominally deflects the incoming flow by. The Reynolds number based on the incoming boundary-layer thickness of is considerably higher than in previous LES studies. The very long integration time of allows for an accurate analysis of low-frequency unsteady effects. Experimental wall-pressure measurements are in good agreement with the LES data. Both datasets exhibit the distinct plateau within the separated-flow region of a strong SWBLI. The filtered three-dimensional flow field shows clear evidence of counter-rotating streamwise vortices originating in the proximity of the bubble apex. Contrary to previous numerical results on compression ramp configurations, these Gortler-like vortices are not fixed at a specific spanwise position, but rather undergo a slow motion coupled to the separation-bubble dynamics. Consistent with experimental data, power spectral densities (PSD) of wall-pressure probes exhibit a broadband and very energetic low-frequency component associated with the separation-shock unsteadiness. Sparsity-promoting dynamic mode decompositions (SPDMD) for both spanwise-averaged data and wall-plane snapshots yield a classical and well-known low-frequency breathing mode of the separation bubble, as well as a medium-frequency shedding mode responsible for reflected and reattachment shock corrugation. SPDMD of the two-dimensional skin-friction coefficient further identifies streamwise streaks at low frequencies that cause large-scale flapping of the reattachment line. The PSD and SPDMD results of our impinging SWBLI support the theory that an intrinsic mechanism of the interaction zone is responsible for the low-frequency unsteadiness, in which Gortler-like vortices might be seen as a continuous (coherent) forcing for strong SWBLI.

118 citations


Journal ArticleDOI
01 Sep 2017
TL;DR: In this paper, the authors present detailed observations of the shock waves emitted at the collapse of single cavitation bubbles using simultaneous time-resolved shadowgraphy and hydrophone pressure measurements.
Abstract: We present detailed observations of the shock waves emitted at the collapse of single cavitation bubbles using simultaneous time-resolved shadowgraphy and hydrophone pressure measurements. The geometry of the bubbles is systematically varied from spherical to very nonspherical by decreasing their distance to a free or rigid surface or by modulating the gravity-induced pressure gradient aboard parabolic flights. The nonspherical collapse produces multiple shocks that are clearly associated with different processes, such as the jet impact and the individual collapses of the distinct bubble segments. For bubbles collapsing near a free surface, the energy and timing of each shock are measured separately as a function of the anisotropy parameter zeta, which represents the dimensionless equivalent of the Kelvin impulse. For a given source of bubble deformation (free surface, rigid surface, or gravity), the normalized shock energy depends only on zeta, irrespective of the bubble radius R-0 and driving pressure Delta p. Based on this finding, we develop a predictive framework for the peak pressure and energy of shock waves from nonspherical bubble collapses. Combining statistical analysis of the experimental data with theoretical derivations, we find that the shock peak pressures can be estimated as jet impact-induced hammer pressures, expressed as p(h) = 0.45(rho c(2) Delta p)(1/2) zeta(-1) at zeta > 10(-3). The same approach is found to explain the shock energy decreasing as a function of zeta(-2/3).

116 citations


Journal ArticleDOI
25 Oct 2017-Nature
TL;DR: X-ray diffraction experiments with femtosecond resolution are presented that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation, and find a transition from twinning to dislocation-slip-dominated plasticity at high pressure.
Abstract: Pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites, the formation of interstellar dust clouds, ballistic penetrators, spacecraft shielding and ductility in high-performance ceramics. At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation is challenging. Experiments that characterized lattice defects have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials, but have only recently been applied to plasticity during shock compression and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum-an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations and experiments have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks, we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. The techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.

104 citations


Journal ArticleDOI
TL;DR: The current shock classification scheme of meteorites assigns shock levels of S1 (unshocked) to S6 (very strongly shocked) using shock effects in rock-forming minerals such as olivine and plagioclase.
Abstract: The current shock classification scheme of meteorites assigns shock levels of S1 (unshocked) to S6 (very strongly shocked) using shock effects in rock-forming minerals such as olivine and plagioclase. The S6 stage (55–90 GPa; 850–1750 °C) relies solely on localized effects in or near melt zones, the recrystallization of olivine, or the presence of mafic high-pressure phases such as ringwoodite. However, high whole rock temperatures and the presence of high-pressure phases that are unstable at those temperatures and pressures of zero GPa (e.g., ringwoodite) are two criteria that exclude each other. Each type of high-pressure phase provides a minimum shock pressure during elevated pressure conditions to allow the formation of this phase, and a maximum temperature of the whole rock after decompression to allow the preservation of this phase. Rocks classified as S6 are characterized not by the presence but by the absence of those thermally unstable high-pressure phases. High-pressure phases in or attached to shock melt zones form mainly during shock pressure decline. This is because shocked rocks (<60 GPa) experience a shock wave with a broad isobaric pressure plateau only during low velocity (<4.5 km s−1) impacts, which rarely occur on small planetary bodies; e.g., the Moon and asteroids. The mineralogy of shock melt zones provides information on the shape and temporal duration of the shock wave but no information on the general maximum shock pressure in the whole rock.

102 citations


Journal ArticleDOI
01 Jan 2017
TL;DR: In this article, a parametric study is performed to analyze the effect of inflow pressure P-0, and Mach number M-0 on the initiation structure and length of two-dimensional, oblique detonations from a wedge in a stoichiometric hydrogen-air mixture.
Abstract: The initiation features of two-dimensional, oblique detonations from a wedge in a stoichiometric hydrogen-air mixture are investigated via numerical simulations using the reactive Euler equations with de-tailed chemistry. A parametric study is performed to analyze the effect of inflow pressure P-0, and Mach number M-0 on the initiation structure and length. The present numerical results demonstrate that the two transition patterns, i.e., an abrupt transition from a multi-wave point connecting the oblique shock and the detonation surface and a smooth transition via a curved shock, depend strongly on the inflow Mach number, while the inflow pressure is found to have little effect on the oblique shock-to-detonation transition type. The present results also reveal a slightly more complex structure of abrupt transition type in the case of M-0 = 7.0, consisting of various chemical and gasdynamic processes in the shocked gas mixtures. The present results show quantitatively that the initiation length decreases with increasing M-0, primarily due to the in-crease of post-shock temperature. Furthermore, the effect of M-0 on initiation length is independent of P-0, but given the same M-0, the initiation length is found to be inversely proportional to P-0. Theoretical analysis based on the constant volume combustion (CVC) theory is also performed, and the results are close to the numerical simulations in the case of high M-0 regardless of P-0, demonstrating that the post-oblique-shock condition, i.e., post-shock temperature, is the key parameter affecting the initiation. At decreasing M-0, the CVC theory breaks down, suggesting a switch from chemical kinetics-controlled to a wave-controlled gasdynamic process. For high inflow pressure P-0 at decreasing M-0, the CVC theoretical estimations depart from numerical results faster than those of low P-0, due to the presence of the non-monotonic effects of chemical kinetic limits in hydrogen oxidation at high pressure. (C) 2016 by The Combustion Institute. Published by Elsevier Inc.

88 citations



Journal ArticleDOI
TL;DR: In this paper, a 3D transient mathematical model of chemically reacting gas mixture flows incorporating hydrogen air mixtures was developed to study detonation initiation due to focusing of a shock wave reflected inside a cone.

76 citations


Journal ArticleDOI
TL;DR: In this paper, a continuum wave reflection theory and a resolved shear stress model were proposed to explain the distribution of dislocation nucleation sites in the low latitude region near the equator of the spherical void surfaces.

71 citations


Journal ArticleDOI
TL;DR: High-speed emission spectroscopy revealed that 50 ns after flyer plate impacts, an emission pulse was generated by ZIF-8 resulting from chemical bonds that were broken and subsequently reformed, indicating MOFs may prove useful in the dissipation of shock wave energy through large structural changes.
Abstract: Metal–organic frameworks (MOFs) have potential applications as energy absorbing materials for shock wave energy mitigation due to their nanoporosity. Here we have examined km/s laser-driven flyer plate impacts on a prototypical MOF, ZIF-8. We observed particle fragmentation and morphological changes in microcrystals of ZIF-8 at lower shock pressures (≈2.5 GPa), and amorphization and structural collapse at higher pressures (≈8 GPa). High-speed emission spectroscopy revealed that 50 ns after flyer plate impacts, an emission pulse was generated by ZIF-8 resulting from chemical bonds that were broken and subsequently reformed. MOFs may prove useful in the dissipation of shock wave energy through large structural changes (free volume collapse and endothermic bond breakage).

70 citations


Journal ArticleDOI
TL;DR: The results show evidence for a critical transition of the dispersive shock into a self-cavitating state and a fully quantitative test of the Whitham modulation theory applied to the universal defocusing nonlinear Schrödinger equation.
Abstract: We investigate the temporal photonic analogue of the dam-break phenomenon for shallow water by exploiting a fiber optics setup. We clearly observe the decay of the steplike input (photonic dam) into a pair of oppositely propagating rarefaction wave and dispersive shock wave. Our results show evidence for a critical transition of the dispersive shock into a self-cavitating state. The detailed observation of the cavitating state dynamics allows for a fully quantitative test of the Whitham modulation theory applied to the universal defocusing nonlinear Schrodinger equation.

Journal ArticleDOI
TL;DR: In this paper, a Smooth Particle Hydrodynamic (SPH) method based on mesh-free Lagrange formulation is applied to simulate an entire process of a shaped-charge detonation, formation of a metal jet as well as penetration on a steel plate.

Journal ArticleDOI
TL;DR: These observations, supported through reshock measurements, provide tight constraints in a regime directly relevant to planetary interiors, in best agreement with density functional theory; however, no one exchange-correlation functional describes well both the onset of dissociation and the maximum compression along the Hugoniot.
Abstract: We present shock compression data for deuterium through the molecular-to-atomic transition along the principal Hugoniot with unprecedented precision, enabling discrimination between subtle differences in first-principle theoretical predictions. These observations, supported through reshock measurements, provide tight constraints in a regime directly relevant to planetary interiors. Our findings are in best agreement with density functional theory; however, no one exchange-correlation functional describes well both the onset of dissociation and the maximum compression along the Hugoniot.

Journal ArticleDOI
TL;DR: In this article, the authors analyze heating and cooling processes in an idealized simulation of a cool core cluster, where momentum-driven AGN feedback balances radiative cooling in a time-averaged sense.
Abstract: We analyze heating and cooling processes in an idealized simulation of a cool-core cluster, where momentum-driven AGN feedback balances radiative cooling in a time-averaged sense. We find that, on average, energy dissipation via shock waves is almost an order of magnitude higher than via turbulence. Most of the shock waves in the simulation are very weak shocks with Mach numbers smaller than 1.5, but the stronger shocks, although rare, dissipate energy more effectively. We find that shock dissipation is a steep function of radius, with most of the energy dissipated within 30 kpc, while radiative cooling loses area less concentrated. However, adiabatic processes and mixing (of post-shock materials and the surrounding gas) are able to redistribute the heat throughout the core. A considerable fraction of the AGN energy also escapes the core region. The cluster goes through cycles of AGN outbursts accompanied by periods of enhanced precipitation and star formation, over Gyr timescales. The cluster core is under-heated at the end of each cycle, but over-heated at the peak of the AGN outburst. During the heating-dominant phase, turbulent dissipation alone is often able to balance radiative cooling at every radius but, when this is occurs, shock waves inevitably dissipate even more energy. Our simulation explains why some clusters, such as Abell 2029, are cooling dominated, while in some other clusters, such as Perseus, various heating mechanisms including shock heating, turbulent dissipation and bubble mixing can all individually balance cooling, and together, overheat the core.

Journal ArticleDOI
TL;DR: In this article, the authors present detailed observations of the shock waves emitted at the collapse of single cavitation bubbles using simultaneous time-resolved shadowgraphy and hydrophone pressure measurements.
Abstract: We present detailed observations of the shock waves emitted at the collapse of single cavitation bubbles using simultaneous time-resolved shadowgraphy and hydrophone pressure measurements. The geometry of the bubbles is systematically varied from spherical to very non-spherical by decreasing their distance to a free or rigid surface or by modulating the gravity-induced pressure gradient aboard parabolic flights. The non-spherical collapse produces multiple shocks that are clearly associated with different processes, such as the jet impact and the individual collapses of the distinct bubble segments. For bubbles collapsing near a free surface, the energy and timing of each shock are measured separately as a function of the anisotropy parameter $\zeta$, which represents the dimensionless equivalent of the Kelvin impulse. For a given source of bubble deformation (free surface, rigid surface or gravity), the normalized shock energy depends only on $\zeta$, irrespective of the bubble radius $R_{0}$ and driving pressure $\Delta p$. Based on this finding, we develop a predictive framework for the peak pressure and energy of shock waves from non-spherical bubble collapses. Combining statistical analysis of the experimental data with theoretical derivations, we find that the shock peak pressures can be estimated as jet impact-induced hammer pressures, expressed as $p_{h} = 0.45\left(\rho c^{2}\Delta p\right)^{1/2} \zeta^{-1}$ at $\zeta > 10^{-3}$. The same approach is found to explain the shock energy quenching as a function of $\zeta^{-2/3}$.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the unsteady pressure fluctuation characteristics in the process of breakup and shedding of unstrainedy sheet/cloud cavitating flows via combined experimental and computational methods.

Journal ArticleDOI
TL;DR: In this article, numerical simulations using Euler equations with detailed chemistry are performed to investigate the effect of fuel-air composition inhomogeneity on the oblique detonation wave (ODW) initiation in hydrogen-air mixtures.

Journal ArticleDOI
TL;DR: In this paper, a study of the structure of 145 low Mach number (M ≤ 3), low beta (β≤ 1), quasi-perpendicular interplanetary collisionless shock waves observed by the Wind spacecraft has provided strong evidence that these shocks have large amplitude whistler precursors.
Abstract: A study of the structure of 145 low Mach number (M ≤ 3), low beta (β≤ 1), quasi-perpendicular interplanetary collisionless shock waves observed by the Wind spacecraft has provided strong evidence that these shocks have large amplitude whistler precursors. The common occurrence and large amplitudes of the precursors raise doubts about the standard assumption that such shocks can be classified as laminar structures. This directly contradicts standard models. In 113 of the 145 shocks (∼78%), we observe clear evidence of magnetosonic-whistler precursor fluctuations with frequencies ∼0.1–7 Hz. We find no dependence on the upstream plasma beta, or any other shock parameter, for the presence or absence of precursors. The majority (∼66%) of the precursors propagate at ≤45∘ with respect to the upstream average magnetic field and most (∼87%) propagate ≥30∘ from the shock normal vector. Further, most (∼79%) of the waves propagate at least 20° from the coplanarity plane. The peak-to-peak wave amplitudes (δBpk − pk) are large with a range of maximum values for the 113 precursors of ∼0.2–13 nT with an average of ∼3 nT. When we normalize the wave amplitudes to the upstream averaged magnetic field and the shock ramp amplitude, we find average values of ∼50% and ∼80%, respectively.

Journal ArticleDOI
TL;DR: In this paper, the radio-to-X-ray phenomenology in a consistent framework was investigated and the existence of two distinct modes differing in their intrabinary shock orientation, distinguished by the phase-centering of the double-peaked X-ray orbital modulation originating from mildlyrelativistic Doppler boosting.
Abstract: Multiwavelength follow-up of unidentified Fermi sources has vastly expanded the number of known galactic-field "black widow" and "redback" millisecond pulsar binaries. Focusing on their rotation-powered state, we interpret the radio to X-ray phenomenology in a consistent framework. We advocate the existence of two distinct modes differing in their intrabinary shock orientation, distinguished by the phase-centering of the double-peaked X-ray orbital modulation originating from mildly-relativistic Doppler boosting. By constructing a geometric model for radio eclipses, we constrain the shock geometry as functions of binary inclination and shock stand-off R(sub 0). We develop synthetic X-ray synchrotron orbital light curves and explore the model parameter space allowed by radio eclipse constraints applied on archetypal systems B1957+20 and J1023+0038. For B1957+20, from radio eclipses the stand-off is R(sub 0) approximately 0:15 - 0:3 fraction of binary separation from the companion center, depending on the orbit inclination. Constructed X-ray light curves for B1957+20 using these values are qualitatively consistent with those observed, and we find occultation of the shock by the companion as a minor influence, demanding significant Doppler factors to yield double peaks. For J1023+0038, radio eclipses imply R(sub 0) is approximately less than 0:4 while X-ray light curves suggest 0:1 is approximately less than R(sub 0) is approximately less than 0:3 (from the pulsar). Degeneracies in the model parameter space encourage further development to include transport considerations. Generically, the spatial variation along the shock of the underlying electron power-law index should yield energy-dependence in the shape of light curves motivating future X-ray phase-resolved spectroscopic studies to probe the unknown physics of pulsar winds and relativistic shock acceleration therein.

Journal ArticleDOI
Jiakai Zhu1, Huangjun Xie1, Kesong Feng1, Xiaobin Zhang1, Minqiang Si1 
TL;DR: In this article, the dynamic cavitation characteristics of liquid nitrogen flow through a transparent venturi tube are experimentally investigated in a variable pressure ratio tunnel, and the analysis on the measured dynamic pressure data and images reveal that the shedding frequency and length of cavity linearly increases, while the pressure amplitude exponentially increases, as the pressure ratio increases.

Journal ArticleDOI
Nan Li1, Juntao Chang1, Kejing Xu1, Daren Yu1, Wen Bao1, Yanping Song1 
TL;DR: In this article, a low-order dynamic model of the shock train has been constructed with the help of the free interaction theory and a 1-D analysis approach, and the results show that the model has the capability of qualitatively analyzing the shock-train behavior.
Abstract: Oblique shock waves are unavoidable in a rectangular hypersonic inlet, leading to a non-uniform flow field. While a significant body of the literature exists regarding the shock train modeling in a uniform incoming flow condition, few efforts have focused on the shock train behavior considering the influence of the shock wave boundary layer interactions. A low-order dynamic model of the shock train has been constructed with the help of the free interaction theory and a 1-D analysis approach. Experimental and numerical investigations have been carried out to evaluate the low-order model. The results show that the model has the capability of qualitatively analyzing the shock train behavior. In the cases with incident shocks, the rapid forward movement of the shock train has been observed by experiment. Besides this phenomenon was also modeled using the low-order model. Schlieren images show that when the shock train approaches the interaction zone, its behavior is characterized by oscillation and then follo...

Journal ArticleDOI
TL;DR: In this paper, a holographic study of coupling-dependent heavy ion collisions was conducted by analyzing the effects of leading-order, inverse coupling constant corrections in a theory with curvature-squared terms.
Abstract: We initiate a holographic study of coupling-dependent heavy ion collisions by analyzing, for the first time, the effects of leading-order, inverse coupling constant corrections In the dual description, this amounts to colliding gravitational shock waves in a theory with curvature-squared terms We find that, at intermediate coupling, nuclei experience less stopping and have more energy deposited near the light cone When the decreased coupling results in an 80% larger shear viscosity, the time at which hydrodynamics becomes a good description of the plasma created from high energy collisions increases by 25% The hydrodynamic phase of the evolution starts with a wider rapidity profile and smaller entropy

Journal ArticleDOI
TL;DR: In this article, the effect of initial conditions on transition to turbulence was studied in a variable-density shock-driven flow, where the initial condition was characterized through proper orthogonal decomposition and density energy spectra from a large set of initial condition images.
Abstract: The effect of initial conditions on transition to turbulence is studied in a variable-density shock-driven flow. Richtmyer–Meshkov instability (RMI) evolution of fluid interfaces with two different imposed initial perturbations is observed before and after interaction with a second shock reflected from the end wall of a shock tube (reshock). The first perturbation is a predominantly single-mode long-wavelength interface which is formed by inclining the entire tube to 80 relative to the horizontal, yielding an amplitude-to-wavelength ratio, , and thus can be considered as half the wavelength of a triangular wave. The second interface is multi-mode, and contains additional shorter-wavelength perturbations due to the imposition of shear and buoyancy on the inclined perturbation of the first case. In both cases, the interface consists of a nitrogen-acetone mixture as the light gas over carbon dioxide as the heavy gas (Atwood number, ) and the shock Mach number is . The initial condition was characterized through Proper Orthogonal Decomposition and density energy spectra from a large set of initial condition images. The evolving density and velocity fields are measured simultaneously using planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) techniques. Density, velocity, and density–velocity cross-statistics are calculated using ensemble averaging to investigate the effects of additional modes on the mixing and turbulence quantities. The density and velocity data show that a distinct memory of the initial conditions is maintained in the flow before interaction with reshock. After reshock, the influence of the long-wavelength inclined perturbation present in both initial conditions is still apparent, but the distinction between the two cases becomes less evident as smaller scales are present even in the single-mode case. Several methods are used to calculate the Reynolds number and turbulence length scales, which indicate a transition to a more turbulent state after reshock. Further evidence of transition to turbulence after reshock is observed in the velocity and density fluctuation spectra, where a scaling close to is observed for almost one decade, and in the enstrophy fluctuation spectra, where a scaling close to is observed for a similar range. Also, based on normalized cross correlation spectra, local isotropy is reached at lower wave numbers in the multi-mode case compared with the single-mode case before reshock. By breakdown of large scales to small scales after reshock, rapid decay can be observed in cross-correlation spectra in both cases.

Journal ArticleDOI
TL;DR: In this paper, the dynamics and radiation of an individual black hole minidisk were studied using two-dimensional hydrodynamical simulations performed with a new general relativistic version of the moving mesh code Disco.
Abstract: Newtonian simulations have demonstrated that accretion onto binary black holes produces accretion disks around each black hole ("minidisks"), fed by gas streams flowing through the circumbinary cavity from the surrounding circumbinary disk. We study the dynamics and radiation of an individual black hole minidisk using two-dimensional hydrodynamical simulations performed with a new general relativistic version of the moving mesh code Disco. We introduce a co-moving energy variable which enables highly accurate integration of these high Mach number flows. Tidally induced spiral shock waves are excited in the disk and propagate through the ISCO providing a Reynolds stress which causes efficient accretion by purely hydrodynamic means and producing a radiative signature brighter in hard X-rays than the Novikov-Thorne model. Disk cooling is provided by a local blackbody prescription that allows the disk to evolve self-consistently to a temperature profile where hydrodynamic heating is balanced by radiative cooling. We find that the spiral shock structure is in agreement with the relativistic dispersion relation for tightly-wound linear waves. We measure the shock induced dissipation and find outward angular momentum transport corresponding to an effective alpha parameter of order 0.01. We perform ray-tracing image calculations from the simulations to produce theoretical minidisk spectra and viewing angle dependent images for comparison with observations.

Journal ArticleDOI
TL;DR: In this article, the reaction zone structure and burning mechanism of unstable detonations were investigated using a large-eddy simulation method where the reactions due to both autoignition and turbulent transport were treated exactly at the subgrid scale in a reaction-diffusion formulation.
Abstract: The present study addresses the reaction zone structure and burning mechanism of unstable detonations. Experiments investigated mainly two-dimensional methane–oxygen cellular detonations in a thin channel geometry. The sufficiently high temporal resolution permitted the determination of the probability density function of the shock distribution, a power law with an exponent of $-3$ , and the burning rate of unreacted pockets from their edges – through surface turbulent flames with a speed approximately 3–7 times larger than the laminar one at the local conditions. Numerical simulations were performed using a novel large-eddy simulation method where the reactions due to both autoignition and turbulent transport were treated exactly at the subgrid scale in a reaction–diffusion formulation. The model is an extension of Kerstein and Menon’s linear eddy model for large-eddy simulation to treat flows with shock waves and rapid gas-dynamic transients. The two-dimensional simulations recovered well the amplification of the laminar flame speed due to the turbulence generated mainly by the shear layers originating from the triple points and subsequent Richtmyer–Meshkov instability associated with the internal pressure waves. The simulations clarified how the level of turbulence generated controlled the burning rate of the pockets, the hydrodynamic thickness of the wave, the cellular structure and its distribution. Three-dimensional simulations were found to be in general good agreement with the two-dimensional ones, in that the subgrid-scale model captured the ensuing turbulent burning once the scales associated with the cellular dynamics, where turbulent kinetic energy is injected, are well resolved.

Journal ArticleDOI
TL;DR: In this article, a large-eddy simulation of a supersonic lifted jet flame was performed by Cheng et al. The results showed that the highly unstable flame base exhibits a cyclic period of around 0.25 milliseconds, with the transient occurence of shock diamonds.

Journal ArticleDOI
TL;DR: In this paper, a series of cases with varying acoustic impedance ratios between the inert and reactant gases, Z, were studied to explore the influence of acoustic impedance mismatch on the propagation of a detonation through the reactant layer.

Journal ArticleDOI
TL;DR: In this paper, high strain-rate loading molecular dynamics simulations were used to investigate the spall behavior of single and nanocrystalline SiC samples, both for both classical and micro-spall regimes, and the predicted spall strength was at maximum along the [111] direction, at 34 GPa, followed by the [110, and [001] directions, at 32 and 30 GPa.

Journal ArticleDOI
TL;DR: In this paper, the authors numerically simulate gravitational shock wave collisions in a holographic model dual to a non-conformal four-dimensional gauge theory and find two novel effects associated to the nonzero bulk viscosity of the resulting plasma.
Abstract: We numerically simulate gravitational shock wave collisions in a holographic model dual to a non-conformal four-dimensional gauge theory. We find two novel effects associated to the non-zero bulk viscosity of the resulting plasma. First, the hydrodynamization time increases. Second, if the bulk viscosity is large enough then the plasma becomes well described by hydrodynamics before the energy density and the average pressure begin to obey the equilibrium equation of state. We discuss implications for the quark-gluon plasma created in heavy ion collision experiments.

Journal ArticleDOI
TL;DR: In this paper, numerical analysis of scramjet combustor has been carried out with different passive techniques to improve the mixing efficiency of supersonic airstream and hydrogen fuel, and it is concluded that highest mixing and combustion efficiency is identified with a uniform zigzag (wavy wall) surface combustor wall design.