摘要:

Essentially exact closures are presented for the second‐ and third‐moment rate equations for diffusion of a pollutant released at a particular time in homogeneous turbulence. The quasi‐Gaussian closure is found to require addition of a down‐gradient diffusion term. Explicit dependence upon the time after release is found to be retained by the highest moment gradient term. The second‐ and third‐moment approaches are therefore concluded to be inherently incapable of accurately solving the general problem of pollutants released at different places at different times.

ISSN:0031-9171    

DOI:10.1063/1.862257

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The linear spin up problem is solved for a rapidly rotating ideal gas of constant temperature. A perturbation solution for small Mach numbers and a numerical solution for finite Mach numbers are given. For finite Mach numbers, several unexpected phenomena occur. For instance, after some time the radial velocity reverses near the center of the container in spite of the fact that gas is sucked into the Ekman layers.

ISSN:0031-9171    

DOI:10.1063/1.862258

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The transonic flow of a vibrationally relaxing or a chemically reacting gas in a convergent‐divergent nozzle is considered. The procedure used to solve the flow equations is similar to that first used by Hall, and the solution is based on a series expansion in terms of the wall geometry in the transonic region. The nonuniformities of the flow properties across the flow field are taken into consideration. Taulbee and Boraas have already solved such a problem for a frozen flow by a sort of inverse method, in which the governing equations are written with the stream function as an independent variable so as to accomodate the variations in flow properties across the flow field. The problem is solved by a direct method, in which the flow equations are written with generalized coordinates of curvilinear coordinates comprising the streamlines and the system of lines normal to the streamlines, and analytical solutions are obtained for both frozen and equilibrium flows.

ISSN:0031-9171    

DOI:10.1063/1.862259

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Analysis is made of a laser supported detonation wave using Whitham’s rule. TheC+characteristic is developed for absorption of laser energy immediately behind a shock wave. The characteristic is then coupled with the Rankine‐Hugoniot equations relating conditions across the shock. In this way an equation for predicting the transient shock strength is obtained. The result is compared to experiment and to steady state laser supported detonation theory. The result of this comparison is that the derived equation does duplicate the transient response of the experiment and (when allowed to run to steady state) it does agree with many of the characteristics of the steady state theory.

ISSN:0031-9171    

DOI:10.1063/1.862260

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A wall‐stabilized arc has been operated at various currents in air at 1 atm pressure. Measurements have been made of the axial electrical field strength, the emitted radiation, and the radial temperature profiles. These data were used to deduce the electrical conductivity, the emission coefficient for optically thin radiation, and the thermal conductivity as a function of temperature. The deduced values are found to be in accord with theoretical computations.

ISSN:0031-9171    

DOI:10.1063/1.862261

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A theory of magnetohydrodynamic piston‐driven disturbances in a thermally‐conducting medium is presented, based on a phenomenological model which admits self‐similar solutions. The motion consists of a thermal precursor followed by an isothermal shock. The magnetic field plays a fundamental role; even a very modest transverse magnetic field keeps the peak densities down, blocks the heat flow, and widens the perturbed domain. This, together with a decrease (increase) of post shock density (temperature) compares favorably with some measurements in the solar wind.

ISSN:0031-9171    

DOI:10.1063/1.862262

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The density profile modification which is generated by the radiation pressure of a powerful laser normally irradiating a spherical target is considered. Numerical simulation with a fluid code shows the formation of a nonmonotonic density profile, with an overdense bump detached in the underdense region. This shape is explained by a stationary model, and except for very small laser fields it, is shown to be the only one‐dimensionally stable solution.

ISSN:0031-9171    

DOI:10.1063/1.862263

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The energy loss of energetic protons in heavy metal targets is calculated at temperatures and densities of interest for pellet fusion. The contributions of bound and free electrons to the stopping power are considered. It is found that in the temperature range of interest the increase in the number of free electrons in the target plasma causes range shortening with increasing temperatures and specific volumes. In order to study this effect on the ablation process, a one‐dimensional calculation of the hydrodynamic flow with energy deposition was carried out.

ISSN:0031-9171    

DOI:10.1063/1.862264

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The spectrum of frequencies and growth rates of the linearized magnetohydrodynamic motion about rotating straight theta pinch equilibria is investigated. A qualitative picture is obtained of the distribution of eigenvalues in the complex plane, and of their dependence on equilibrium parameters and the three mode numbers. A numerical procedure is described which uses this picture for computing the eigenvalue with any given triple of mode numbers. It is shown that rigidly rotating equilibria are unstable unless the mass density is an increasing function of radius; computations indicate that rotation shear (within practical limits) cannot stabilize confined equilibria.

ISSN:0031-9171    

DOI:10.1063/1.862265

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A flat‐ended variant of a multi‐electrode electrostatic plasma probe design, previously proposed by Laframboise and Parker, is described. The probe consists of a collector, a guard, and a sleeve electrode. Besides being easier to construct, this modified probe geometry is more amenable to numerical verification of its operating properties. Such a verification is carried out by numerically following selected collisionless orbits of charged particles in the electric field of the probe. By the same means, an orbit‐limited operating regime of electrode bias combinations is also found. It is found that if the sleeve is given an attractive bias at least three times as large as that of the collector and guard, relative to space potential, then one achieves the intended probe operation, which simulates that of an orbit‐limited spherical Langmuir probe in collisionless conditions but with certain restrictions on probe operation removed or relaxed. It is concluded that experimental tests of the proposed probe configuration are desirable.

ISSN:0031-9171    

DOI:10.1063/1.862266

出版商:AIP    

年代:1978

数据来源: AIP