摘要 :
A self-similar solution for the propagation of a cylindrical shock wave in a dusty gas with heat conduction and radiation heat flux, which is rotating about the axis of symmetry, is investigated. The shock is assumed to be driven ...
展开
A self-similar solution for the propagation of a cylindrical shock wave in a dusty gas with heat conduction and radiation heat flux, which is rotating about the axis of symmetry, is investigated. The shock is assumed to be driven out by a piston (an inner expanding surface) and the dusty gas is assumed to be a mixture of non-ideal gas and small solid particles. The density of the ambient medium is assumed to be constant. The heat conduction is expressed in terms of Fourier’s law and radiation is considered to be of diffusion type for an optically thick grey gas model. The thermal conductivity K and the absorption coefficient ~R are assumed to vary with temperature and density. Similarity solutions are obtained, and the effects of variation of the parameter of non-idealness of the gas in the mixture, the mass concentration of solid particles and the ratio of density of solid particles to the initial density of the gas are investigated.
收起
摘要 :
We model the propagation of a coronal shock wave, using nonlinear geometrical acoustics. The method is based on the Wentzel-Kramers-Brillouin (WKB) approach and takes into account the main properties of nonlinear waves: i) depende...
展开
We model the propagation of a coronal shock wave, using nonlinear geometrical acoustics. The method is based on the Wentzel-Kramers-Brillouin (WKB) approach and takes into account the main properties of nonlinear waves: i) dependence of the wave front velocity on the wave amplitude, ii) nonlinear dissipation of the wave energy, and iii) progressive increase in the duration of solitary shock waves. We address the method in detail and present results of the modeling of the propagation of shock-associated extreme-ultraviolet (EUV) waves as well as Moreton waves along the solar surface in the simplest solar corona model. The calculations reveal deceleration and lengthening of the waves. In contrast, waves considered in the linear approximation keep their length unchanged and slightly accelerate.
收起
摘要 :
We model the propagation of a coronal shock wave, using nonlinear geometrical acoustics. The method is based on the Wentzel–Kramers–Brillouin (WKB) approach and takes into account the main properties of nonlinear waves: i) depen...
展开
We model the propagation of a coronal shock wave, using nonlinear geometrical acoustics. The method is based on the Wentzel–Kramers–Brillouin (WKB) approach and takes into account the main properties of nonlinear waves: i) dependence of the wave front velocity on the wave amplitude, ii) nonlinear dissipation of the wave energy, and iii) progressive increase in the duration of solitary shock waves. We address the method in detail and present results of the modeling of the propagation of shock-associated extreme-ultraviolet (EUV) waves as well as Moreton waves along the solar surface in the simplest solar corona model. The calculations reveal deceleration and lengthening of the waves. In contrast, waves considered in the linear approximation keep their length unchanged and slightly accelerate.
收起
摘要 :
The propagation speed of a shock or detonation wave in a shock tube is usually determined by a time-of-flight method by dividing the distance between two transducers with the propagation time of the disturbance signal. Some arbitr...
展开
The propagation speed of a shock or detonation wave in a shock tube is usually determined by a time-of-flight method by dividing the distance between two transducers with the propagation time of the disturbance signal. Some arbitrariness is inherent in determining the propagation time by this method. An improved method for objectively determining the propagation time using a nonstationary cross-correlation technique is described. The method requires the choice of an integration window that includes the nonstationary event. The method was first tested against a number of model functions with different noise levels. It was then applied to propagating and reflected shock and detonation waves, including an example of a transitioning detonation wave propagating past six transducers. In addition, the nonstationary CCF technique was also applied to evaluate the uncertainty in estimating the deflagration-to-detonation transition run-up distance. In all cases, the time delay and its standard deviation could be obtained.
收起
摘要 :
The present paper contains a detailed study of shock wave reflection from a wedge placed in various suspensions. In past works, the incident shock propagated initially in pure gas and the suspension started only at the leading edg...
展开
The present paper contains a detailed study of shock wave reflection from a wedge placed in various suspensions. In past works, the incident shock propagated initially in pure gas and the suspension started only at the leading edge of the deflecting wedge. However, in the present case the entire flow field is filled with a gas-dust suspension and the initial shock wave has steady-state structure relative to the shock front. In former studies the transmitted shock wave starts its propagation into the suspension and is reflected from the wedge at the same time. It is therefore obvious that the two unrelated processes of (2D) reflection and (1D) "transitional" relaxation occur simultaneously. In the present case the suspension behind the incident shock wave has reached steady state (i.e., it is a traveling wave) before the shock reaches the wedge leading edge.The reflection process from the deflecting wedge is studied for different dust mass loadings and different dust-particle diameter. It is shown that when the dust loading is low and the dust particle diameter is small the wave reflection pattern is similar to that observed in a similar pure gas case. In addition, an equilibrium state is reached, behind the evolved waves, very quickly. On the other hand, when the dust loading is relatively high and/or the dust particle diameter is relatively large, the observed reflection wave pattern is very different from that seen in a similar pure gas case. In such cases it takes much longer time to reach an equilibrium state behind the reflecting waves. It is also shown that the dust presence significantly affects the (gas) pressure on the wedge surface. The higher the dust loading is, the higher the pressure on the wedge surface. Suspensions composed of solid particle of different size, but having the same dust mass loading, will approach the same equilibrium pressure. However, it will take longer time to reach an equilibrium state for suspensions having large diameter particles. (C) 2004 Elsevier Ltd. All rights reserved.
收起
摘要 :
The propagation of a planar shock wave through a split channel is both experimentally and numerically studied. Experiments were conducted in a square cross-sectional shock tube having a main channel which splits into two symmetric...
展开
The propagation of a planar shock wave through a split channel is both experimentally and numerically studied. Experiments were conducted in a square cross-sectional shock tube having a main channel which splits into two symmetric secondary channels, for three different shock wave Mach numbers ranging from about 1.1 to 1.7. High-speed schlieren visualizations were used along with pressure measurements to analyze the main physical mechanisms that govern shock wave diffraction. It is shown that the flow behind the transmitted shock wave through the bifurcation resulted in a highly two-dimensional unsteady and non-uniform flow accompanied with significant pressure loss. In parallel, numerical simulations based on the solution of the Euler equations with a second-order Godunov scheme confirmed the experimental results with good agreement. Finally, a parametric study was carried out using numerical analysis where the angular displacement of the two channels that define the bifurcation was changed from 90 degrees, 45 degrees, 20 degrees, and 0 degrees. We found that the angular displacement does not significantly affect the overpressure experience in either of the two channels and that the area of the expansion region is the important variable affecting overpressure, the effect being, in the present case, a decrease of almost one half.
收起
摘要 :
Experimental studies conducted during the 70s and 80s of the previous century are numerically simulated. We examine a horizontal duct with a vertical branch having a circular cross section whose diameter is 5 cm. These experiments...
展开
Experimental studies conducted during the 70s and 80s of the previous century are numerically simulated. We examine a horizontal duct with a vertical branch having a circular cross section whose diameter is 5 cm. These experiments were conducted by the late Dr Heilig in the Ernst-Mach-lnstitute (private communication). In both segments of the branched duct pressure transducers were installed. They were used for recording the pressure histories and for deducing the traveling shock wave speed. These results were compared with the present numerical simulation. The numerical simulations were conducted using the commercial code Fluent with the density-based AUSM solver. The solver is second order in both space and time. It is apparent from the results obtained that good agreement exists between the recorded pressure histories and their simulations. Based on the good agreement between recorded and simulated pressures a numerical study was conducted by comparison between two similar branched ducts, one having a circular cross section while the other has a rectangular cross section. Also, the effect that changes in the branched segment orientation have on the resulting flow field were investigated.
收起
摘要 :
We present the results of analytical modelling of fast-mode magnetohydrodynamic wave propagation near a 2D magnetic null point. We consider both a linear wave and a weak shock and analyse their behaviour in cold and warm plasmas. ...
展开
We present the results of analytical modelling of fast-mode magnetohydrodynamic wave propagation near a 2D magnetic null point. We consider both a linear wave and a weak shock and analyse their behaviour in cold and warm plasmas. We apply the nonlinear geometrical acoustics method based on the Wentzel-Kramers-Brillouin approximation. We calculate the wave amplitude, using the ray approximation and the laws of solitary shock wave damping. We find that a complex caustic is formed around the null point. Plasma heating is distributed in space and occurs at a caustic as well as near the null point due to substantial nonlinear damping of the shock wave. The shock wave passes through the null point even in a cold plasma. The complex shape of the wave front can be explained by the caustic pattern.
收起
摘要 :
The jumps in Helmholtz free energy and stress across a shock wave front are obtained by using the Taylor's series expansion of the corresponding functions of arbitrarily constrained thermoelastic solids. The linear terms in the ex...
展开
The jumps in Helmholtz free energy and stress across a shock wave front are obtained by using the Taylor's series expansion of the corresponding functions of arbitrarily constrained thermoelastic solids. The linear terms in the expressions of jumps are considered alone to account for linear weak shock waves. The generalized thermomechanical constraint functions and purely mechanical constraint functions are treated separately. In the case of the thermoelastic solids with purely mechanical constraints, the propagation condition of weak shock waves is found to be similar to the propagation condition of homothermal acceleration waves. In the case of the thermoelastic solids with general thermomechanical constraints, the corresponding propagation condition is found to be similar to the propagation condition of homentropic acceleration waves. The speed of propagation of weak shock waves is obtained in a linear thermoelastic solid subject to the purely mechanical constraint of inextensibility.
收起
摘要 :
The evolution of a vortex in glow discharge plasma is studied analytically. Specifically, the mechanism of local energy deposition into the flow by the plasma is considered and its effect on the structure of an inviscid vortex is ...
展开
The evolution of a vortex in glow discharge plasma is studied analytically. Specifically, the mechanism of local energy deposition into the flow by the plasma is considered and its effect on the structure of an inviscid vortex is analyzed. The vortex is modeled by a set of Euler's equations while the energy transferred by the plasma into the gas is represented by Rayleigh mechanism. In this mechanism, the amount of heat addition is a function of local gas density. The analysis indicates that the plasma can have a considerable effect on the structure of a vortex. The inviscid calculations show that in a uniform discharge, a 1 cm vortex dies out in a fraction of a second. (c) 2005 American Institute of Physics.
收起
原文获取