Strong Shock Front Research Articles

Experimental investigation of the emission in the unsteady flow region behind strong shock fronts in mixtures of co and CO2 with nitrogen and argon

Mixtures of CO (or CO2) gases and N2 behind strong shock fronts at temperatures 4000–10 000 ° K have been investigated with a view to elucidating the mechanism of the physicochemical processes in the unsteady region of the gas flow behind a shock front leading to the behavior of strongly radiating CN and C2 molecules and C atoms and also determining the quantitative characteristics of the chemical reactions. A shock tube was used in the investigations, which made it possible to obtain the intensity distribution of the radiation of several components — CN, C2, and C — behind shock fronts.

A method for computing selfgravitating gas flows with radiation

We present a numerical method which is suitable for calculating selfgravitating gas flows including thermodynamic processes and radiation. Such problems arise for example in connection with the formation of new stars by gravitational collapse of interstellar clouds. A particularly difficult problem which must be numerically solved in a consistent way is the settling of matter from a supersonic flow into a hydrostatic equilibrium after passing through a strong shock front. Because this must be done without continuously exciting spurious oscillations with extremely small time scales, very stringent constraints are imposed upon the method of solution. Technically, the method here described incorporates a freely moving coordinate system with a generalized form of Richtmyer's artificial viscosity for smoothing shock fronts (tensor viscosity), the two most important improvements to earlier attempts to solve this problem. The method has been extensively tested for spherically and axially symmetric flows. How to proceed in the full 3D case is briefly outlined. Accuracy problems are discussed in connection with numerical stability. We give examples for collapse, accretion and explosion in spherical symmetry and for collapse and ring formation in an axially symmetric rotating cloud.

Resistance to shock-front propagation in solids

The structure of a strong shock front is modeled using a wall of dislocations. Motion of these dislocations changes the density of the solid medium and simultaneously relaxes the shear strains that would otherwise exist behind the front. The dislocation motion is highly dissipative because it requires atoms in intimate contact to slide over one another. This transports momentum down the velocity gradient. It is shown that the energy dissipation rate associated with dislocation motion is larger than for any other general mechanism in the system, including electron-electron, electron-phonon, and phonon-phonon interactions. The reason for this is that electrons are not effective in transporting momentum, and atomic thermal velocities are substantially smaller than the velocities of the dislocations which move with the shock front. The viscosity coefficient associated with the dislocations is propertional to the shock velocity, so the viscous drag stress is proportional to the square of the shock velocity. This can lead to large drag pressures.

Form of distribution of absolute and relative velocities of molecules in a strong shock front. Monatomic one-component gas

Form of distribution of absolute and relative velocities of molecules in a strong shock front. Monatomic one-component gas

Accretion onto neutron stars under adiabatic shock conditions

view Abstract Citations (128) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Accretion onto neutron stars under adiabatic shock conditions. Shapiro, S. L. ; Salpeter, E. E. Abstract The accretion of gas onto a neutron star is examined for the case in which a strong adiabatic shock front forms above the stellar surface to decelerate the incident plasma stream. Steady-state spherically symmetric flow is considered, all magnetic fields are ignored, and rapid thermalization by plasma instabilities in the shock front is assumed. The dynamic and thermal structure of the emission zone between the surface and the shock front is determined, and the emergent radiation spectrum is calculated. In many cases an appreciable fraction (about one-quarter) of the total energy is emitted in the form of gamma-ray photons between 1 and 10 MeV. The possible relevance of the model calculations to observations of galactic X-ray sources and gamma-ray bursts is discussed. Publication: The Astrophysical Journal Pub Date: June 1975 DOI: 10.1086/153645 Bibcode: 1975ApJ...198..671S Keywords: Adiabatic Conditions; Neutron Stars; Shock Fronts; X Ray Sources; Astronomical Models; Galactic Radiation; Gamma Rays; Magnetohydrodynamic Stability; Mass Transfer; Plasma Dynamics; Radiation Spectra; Steady Flow; Thermalization (Energy Absorption); Astrophysics full text sources ADS |

Shapes of strong shock fronts in an inhomogeneous solar wind

The shapes expected for solar-flare-produced strong shock fronts in the solar wind have been calculated, large-scale variations in the ambient medium being taken into account. A linear mathematical model was used, based on the assumptions that (1) the pressure immediately behind a shock front is constant over the surface of the front, (2) the variations in the ambient medium are time stationary in a frame of reference corotating with the sun, and (3) the effects of the interplanetary magnetic field can be neglected. The shock fronts were assumed to be spherically symmetric near the sun. It has been shown that for reasonable ambient solar wind conditions the mean and the standard deviation of the east-west shock normal angle are in agreement with experimental observations including shocks of all strengths. The results further suggest that near a high-speed stream it is difficult to distinguish between corotating shocks and flare-associated shocks on the basis of the shock normal alone. Although the calculated shapes are outside the range of validity of the linear approximation, these results indicate that the variations in the ambient solar wind may account for large deviations of shock normals from the radial direction.

Effect of vibrational relaxation of molecules on dissociating air characteristics behind a strong shock front

Molecular vibrational relaxation has a considerable effect on the dissociation rate in a gas consisting of molecules of a single type [1]. In gas mixtures such as air, vibrational relaxation also affects the other reaction rates, which may be important in solving several problems of hypersonic aerodynamics. This is due to the fact that in air at temperatures above 5000° the vibrational excitation of nitrogen molecules and the dissociation of oxygen molecules proceed almost simultaneously. We study the effect of vibrational relaxation on the conditions behind a strong shock front.

Motion of a strong shock front in a two-dimensional gas layer with moving internal boundary

We examine the problem of planar one-dimensional motion of a strong shock wave with moving internal boundary in which the initial position of the front, its intensity, the mass of the gas involved in the motion, and the energy contained in this gas are known. The problem is not self-similar and its exact solution, which involves working with partial differential equations, presents serious difficulties. In the following we determine the law of shock-front motion in this problem via the method of [1], which makes it possible to find a system of ordinary differential equations for the problem. The method is based on an initial specification of the power-law coupling between the dimensionless Lagrangian and Eulerian variables and replacement of the energy equation by this coupling and the energy integral. The solution is sought in the first approximation.

Airflow behind strong shock front with account for nonequilibrium ionization and radiation

We consider the gas state behind a shock wave front in air with a velocity v≥10 km/sec. Nonequilibrium ionization and radiative transport are taken into account. We take into consideration the real air spectrum — the numerous lines, bands, and continuua. Account for the radiation leads to an integrodifferential system of equations for which a solution method is developed. As a result we obtain the gas parameter profiles behind the shock wave, which are affected by the relaxation processes and radiative cooling. The calculations were made for v=10–16 km/sec and a pressure p=10−5–10−2 atm ahead of the front.

Axisymmetric Shocks in the Newtonian Limit for Nonrigid Boundaries

The natural generalization of the snowplow equation in two-dimensional axisymmetric or Cartesian geometries is a Newtonian approximation in which the possibility of surface deformation is admitted. Such a general Newtonian approximation has been derived from the Lagrangian fluid equations, using an ideal-gas model in the limit of strong shock and high density ratio across the shock front. In one dimension the result reduces properly to the snowplow equation. In two dimensions, if the surface is constrained and the motion steady, the result consists of the ``Newtonian plus Busemann'' terms. The general result contains in addition a Coriolis term. The general theory is applied to the evaluation of the pressure on the surface of a conical plasma whose vertex angle is decreasing uniformly with time. Although the results are derived for an ideal-gas model, they are applicable whenever dissociation and ionization are taking place behind a strong shock front.