scispace - formally typeset
Search or ask a question
Topic

Oblique shock

About: Oblique shock is a research topic. Over the lifetime, 6551 publications have been published within this topic receiving 119823 citations.


Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, a self-consistent theoretical model for collisionless parallel shock structure, based on the hypothesis that shock dissipation and heating can be provided by electromagnetic ion beam-driven instabilities, is presented.
Abstract: This paper presents a self-consistent theoretical model for collisionless parallel shock structure, based on the hypothesis that shock dissipation and heating can be provided by electromagnetic ion beam-driven instabilities. It is shown that shock formation and plasma heating can result from parallel propagating electromagnetic ion beam-driven instabilities for a wide range of Mach numbers and upstream plasma conditions. The theoretical predictions are compared with recently published observations of quasi-parallel interplanetary shocks. It was found that low Mach number interplanetary shock observations were consistent with the explanation that group-standing waves are providing the dissipation; two high Mach number observations confirmed the theoretically predicted rapid thermalization across the shock.

213 citations

Journal ArticleDOI
TL;DR: In this article, the first-order Fermi process at the fast shock was used to accelerate nonthermal electrons in solar flares, and the accelerated electrons are trapped between the two slow shocks due to the magnetic mirror downstream of the fast shocks, thus explaining the impulsive loop top hard X-ray source discovered with Yohkoh.
Abstract: Because of its high injection energy, Fermi acceleration has not been considered to be viable to explain nonthermal electrons (20-100 keV) produced in solar flares. Here we propose that nonthermal electrons are efficiently accelerated by the first-order Fermi process at the fast shock, as a natural consequence of the new magnetohydrodynamic picture of the flaring region revealed with Yohkoh. An oblique fast shock is naturally formed below the reconnection site and boosts the acceleration to significantly decrease the injection energy. The slow shocks attached to the reconnection X-point heat the plasma up to 10-20 MK, exceeding the injection energy. The combination of the oblique shock configuration and the preheating by the slow shock allows bulk electron acceleration from the thermal pool. The accelerated electrons are trapped between the two slow shocks due to the magnetic mirror downstream of the fast shock, thus explaining the impulsive loop-top hard X-ray source discovered with Yohkoh. The acceleration timescale is ~0.3-0.6 s, which is consistent with the timescale of impulsive bursts. When these electrons stream away from the region enclosed by the fast shock and the slow shocks, they are released toward the footpoints and may form the simultaneous double-source hard X-ray structure at the footpoints of the reconnected field lines.

206 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the behavior of converging weak shock waves near three different kinds of focus, and found that the behavior at the focus is nonlinear and that diffraction shocks participate in a Mach reflexion process near the focus, whose development is determined by competition between the convergence of the sides of the focusing front and acceleration of its central portion.
Abstract: This paper reports an experimental investigation, using shadowgraphs and pressure measurements, of the detailed behaviour of converging weak shock waves near three different kinds of focus. Shocks are brought to a focus by reflecting initially plane fronts from concave end walls in a large shock tube. The reflectors are shaped to generate perfect foci, aretes and caustics. It is found that, near the focus of a shock discontinuity, a complex wave field develops, which always has the same basic character, and which is always essentially nonlinear. A diffracted wave field forms behind the non-uniform converging shock; its compressive portions steepen to form diffraction shocks, while diffracted expansion waves overtake and weaken the diffraction shocks. The diffraction shocks participate in a Mach reflexion process near the focus, whose development is determined by competition between the convergence of the sides of the focusing front and acceleration of its central portion. In fact, depending on the aperture of the convergence and the strength of the initial wave, the three-shock intersections of the Mach reflexions either cross on a surface of symmetry or remain uncrossed. In the former case, which is observed if the shock wave is relatively weak, the wavefronts emerge from focus crossed and folded, in accordance with the predictions of geometrical acoustics theory. In the latter, the strong-shock case, the fronts beyond focus are uncrossed, as predicted by the theory of shock dynamics. It is emphasized that in both cases the behaviour at the focus is nonlinear. The overtaking of the diffraction shocks by the diffracted expansions limits the amplitude of the converging wave near focus, and is the mechanism by which the maximum amplification factor observed at focus is determined. In all cases, maximum pressures are limited to rather low values.

203 citations

Journal ArticleDOI
TL;DR: In this paper, large-eddy simulations of supersonic cavity flowfields are performed using a high-order numerical method, which employs a time-implicit approximately factored finite difference algorithm, and applies Newton-like subiterations to achieve second-order temporal and fourth-order spatial accuracy.
Abstract: Large-eddy simulations of supersonic cavity flowfields are performed using a high-order numerical method. Spatial derivatives are represented by a fourth-order compact approximation that is used in conjunction with a sixth-order nondispersive filter. The scheme employs a time-implicit approximately factored finite difference algorithm, and applies Newton-like subiterations to achieve second-order temporal and fourth-order spatial accuracy. The Smagorinsky dynamic subgrid-scale model is incorporated in the simulations to account for the spatially underresolved stresses. Computations at a freestream Mach number of 1.19 are carried out for a rectangular cavity having a length-to-depth ratio of 5:1. The computational domain is described by 2.06×10 7 grid points and has been partitioned into 254 zones, which were distributed on individual processors of a massively parallel computing platform. Active flow control is applied through pulsed mass injection at a very high frequency, thereby suppressing resonant acoustic oscillatory modes

202 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated what kind of phenomena may be expected when a shock wave propagates through a nonuniform medium of decreasing density and reaches the boundary where the density vanishes.
Abstract: An investigation was made as to what kind of phenomena may be expected when a shock wave propagates through a nonuniform medium of decreasing density and reaches the boundary where the density vanishes. This situation may arise for shock waves moving in plasmas sustained by magnetic pressure. (T.R.H.)

201 citations


Network Information
Related Topics (5)
Boundary layer
64.9K papers, 1.4M citations
87% related
Turbulence
112.1K papers, 2.7M citations
86% related
Reynolds number
68.4K papers, 1.6M citations
86% related
Laminar flow
56K papers, 1.2M citations
83% related
Vortex
72.3K papers, 1.3M citations
80% related
Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202369
2022142
2021106
202090
201992
2018102