Nonlinear Rayleigh–Taylor Instability of a Cylindrical Interface in Explosion Flows (original) (raw)
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Two-Dimensional Blast-Wave-Driven Rayleigh-Taylor Instability: Experiment and Simulation
The Astrophysical Journal, 2009
This paper shows results from experiments diagnosing the development of the Rayleigh-Taylor instability with two-dimensional initial conditions at an embedded, decelerating interface. Experiments are performed at the Omega Laser and use ∼5 kJ of energy to create a planar blast wave in a dense, plastic layer that is followed by a lower density foam layer. The single-mode interface has a wavelength of 50 μm and amplitude of 2.5 μm. Some targets are supplemented with additional modes. The interface is shocked then decelerated by the foam layer. This initially produces the Richtmyer-Meshkov instability followed and then dominated by Rayleigh-Taylor growth that quickly evolves into the nonlinear regime. The experimental conditions are scaled to be hydrodynamically similar to SN1987A in order to study the instabilities that are believed to occur at the He/H interface during the blast-wave-driven explosion phase of the star. Simulations of the experiment were performed using the FLASH hydrodynamics code.
Physics of Plasmas, 2009
This paper describes experiments exploring the three-dimensional ͑3D͒ Rayleigh-Taylor instability at a blast-wave-driven interface. This experiment is well scaled to the He/H interface during the explosion phase of SN1987A. In the experiments, ϳ 5 kJ of energy from the Omega laser was used to create a planar blast wave in a plastic disk, which is accelerated into a lower-density foam. These circumstances induce the Richtmyer-Meshkov instability and, after the shock passes the interface, the system quickly becomes dominated by the Rayleigh-Taylor instability. The plastic disk has an intentional pattern machined at the plastic/foam interface. This perturbation is 3D with a basic structure of two orthogonal sine waves with a wavelength of 71 m and an amplitude of 2.5 m. Additional long-wavelength modes with a wavelength of either 212 or 424 m are added onto the single-mode pattern. The addition of the long-wavelength modes was motivated by the results of previous experiments where material penetrated unexpectedly to the shock front, perhaps due to an unintended structure. The current experiments and simulations were performed to explore the effects of this unintended structure; however, we were unable to reproduce the previous results.
Numerical Modeling of the Kinematics of Turbulent Mixing in HE-Driven Blast Waves
fligh-explosive-driven blast waves contain a contact surface (denoting the interface between the detonation products and thu air) which is Rayleigh-Taylor unstable. The kinematics of the mixing at this surface was studied numerically with a onedimensional hydrocode. A k-C turbulence model was used to simulate the growth and decay of turbulence for this problem; source terms were included to model the Rayleigh-Taylor instability Smechanism. The numerical calculations demonstrate that this k-£ JDAM"0"W3 tMvw or I OVO',sOVshOisO.LETz UNCLASSIFIED SECuFAYY CL&S=fICAVIGO o, T•is #Aria (¢wwi ziea Eowm,. UNCLASSIFIED sIuCUQITy CLA.UPICATION OF TWIS *&AG[(11e 0&af SE,SE)
Fluid Structure Interaction between plate and blast waves : Numerical simulations
2019
This study, presents a numerical methodology for fluid-structure interaction between blast waves and plate using the LS Dyna explicit code. The numerical simulation was executed in two stages, (i) a one dimensional calculation was carried out using the balloon analogue and, (ii) the results of 1D calculation were remapped to three dimensions. The explosive used in this study was a mixture of propane and oxygen. The 3D model was able to reproduce the complex reflection phenomenon of shock waves, including the mach stem. A more refined mesh for the air domain shall produce accurate representation of this phenomenon. The aluminum plate was modeled using an elastic plastic constitutive law without damage. Results show that the stress in the plate are beyond its yield limit, therefore, an external damage law coupled to the constitutive law will further improve the results by giving us vital information on damage evolution and rupture.
Fluid Structure Interactions for Blast Wave Mitigation
Journal of Applied Mechanics, 2011
The dynamic response of a free-standing plate subjected to a blast wave is studied numerically to investigate the effects of fluid-structure interaction (FSI) in blast wave mitigation. Previous work on the FSI between a blast wave and a free-standing plate (Kambouchev, N., et al., 2006, “Nonlinear Compressibility Effects in Fluid-Structure Interaction and Their Implications on the Air-Blast Loading of Structures,” J. Appl. Phys., 100(6), p. 063519) has assumed a constant atmospheric pressure at the back of the plate and neglected the resistance caused by the shock wave formation due to the receding motion of the plate. This paper develops an FSI model that includes the resistance caused by the shock wave formation at the back of the plate. The numerical results show that the resistance to the plate motion is especially pronounced for a light plate, and as a result, the previous work overpredicts the mitigation effects of FSI. Therefore, the effects of the interaction between the pla...
Journal of Applied Physics, 2006
The impulse imparted by a blast wave to a freestanding solid plate is studied analytically and numerically focusing on the case in which nonlinear compressibility effects in the fluid are important, as is the case for explosions in air. The analysis furnishes, in effect, an extension of Taylor's pioneering contribution to the understanding of the influence of fluid-structure interaction ͑FSI͒ on the blast loading of structures ͓The Scientific Papers of Sir Geoffrey Ingram Taylor, edited by G. K. Batchelor ͑Cambridge University Press, Cambridge, 1963͒, Vol. III, pp. 287-303͔ to the nonlinear range. The limiting cases of extremely heavy and extremely light plates are explored analytically for arbitrary blast intensity, from where it is concluded that a modified nondimensional parameter representing the mass of compressed fluid relative to the mass of the plate governs the FSI. The intermediate asymptotic FSI regime is studied using a numerical method based on a Lagrangian formulation of the Euler equations of compressible flow and conventional shock-capturing techniques. Based on the analytical and numerical results, an approximate formula describing the entire range of relevant FSI conditions is proposed. The main conclusion of this work is that nonlinear fluid compressibility further enhances the beneficial effects of FSI in reducing the impulse transmitted to the structure. More specifically, it is found that transmitted impulse reductions due to FSI when compared to those obtained ignoring FSI effects are more significant than in the acoustic limit. This result can be advantageously exploited in the design and optimization of structures with increased blast resistance.
Cylindrical blast wave propagation in an enclosure
Shock Waves
A numerical study of propagation and interaction of cylindrical blast waves in an enclosure at different blast intensities is presented. The interest to study such flows stems from the need to bring in an updated description of the flow field and to predict the pressure loads on the structure. An implicit-unfactored high-resolution hybrid Riemann solver for the two-dimensional Euler equations is used. The characteristic values at the cell faces are evaluated by a modified MUSCL scheme. Numerical schlieren-type images are used for understanding the flows qualitatively. The investigation indicated that the resulting flow field is dominated by complex interacting shock systems due to the complex series of shock focusing events, shock-structure and shock-shock interactions. The pressure-load distribution and maximum overpressure are estimated.
Cell-like structure of unstable oblique detonation wave from high-resolution numerical simulation
Proceedings of the Combustion Institute, 2007
A comprehensive numerical study was carried out to investigate the unsteady cell-like structures of oblique detonation waves (ODWs) for a fixed Mach 7 inlet flow over a wedge of 30°turning angle. The effects of grid resolution and activation energy were examined systematically at a dimensionless heat addition of 10. The ODW front remains stable for a low activation energy regardless of grid resolution, but becomes unstable for a high activation energy featuring a cell-like wave front structure. Similar to the situation with an ordinary normal detonation wave (NDW), a continuous increase in the activation energy eventually causes the wave-front oscillation to transit from a regular to an irregular pattern. The wave structure of an unstable ODW, however, differs considerably from that of a NDW. Under the present flow condition, triple points and transverse waves propagate downstream, and the numerical smoke-foil record exhibits traces of triple points that rarely intersect with each other. Several instability-driving mechanisms were conjectured from the highly refined results. Since the reaction front behind a shock wave can be easily destabilized by disturbance inherent in the flowfield, the ODW front becomes unstable and displays cell-like structures due to the local pressure oscillations and/or the reflected shock waves originating from the triple points. The combined effects of various instability sources give rise to a highly unstable and complex flow structure behind an unstable ODW front.
Mix and instability growth from oblique shock
2012
We have studied the formation and evolution of shock-induced mix resulting from interface features in a divergent cylindrical geometry. In this research a cylindrical core of high-explosive was detonated to create an oblique shock wave and accelerate the interface. The interfaces studied were between high-explosive/aluminum, aluminum/plastic, and plastic/air. Surface features added to the aluminum were used to modify this interface. Time sequence radiographic imaging quantified the resulting instability formation from the growth phase to over 60 µs post-detonation, thus allowing the study of the onset of mix and evolution to turbulence. The plastic used here was porous polyethylene. Radiographic image data are compared with numerical simulations of the experiment.
Numerical modelling of oblique shock and detonation waves induced in a wedged channel
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 2008
A computational study of wedge-induced oblique shock and detonation wave phenomena in the flow of a combustible mixture over a wedged channel is presented with the purpose of understanding the fundamental gasdynamics of the waves and their interactions. A two-dimensional, time accurate, finite-volume-based method was used to perform the computations, and a five-species, two-step chemical reaction is assumed for a stoichiometric hydrogen-air mixture. The combustion channel is made of a wedged section followed by a constant area section. The simulation was performed with wedges of up to 20 • semi-angle and Mach numbers from 1.25 to 6, with other inflow parameters fixed. Within the computational domain either propagating or standing shock and detonation wave configurations were obtained depending on the flow Mach number and the wedge semi-angle. Four flow modes, namely, a propagating detonation wave, a standing detonation wave, a propagating shock wave, and a standing shock wave mode were identified. The two detonation-based modes were emphasized. Detonation initiation, propagation, and the induced wave interactions of these modes were investigated. The shock-based modes were also studied briefly. Phenomena explored included overall wave structures, detonation initiation arising from shock coalescence, location of initiation, and double detonation initiation. The physical mechanisms of these phenomena were analysed.