摘要:

An elementary theory is proposed for estimating the strength of pressure waves to be expected from sudden breakdown of a gas by high frequency electromagnetic waves in a one‐dimensional geometry. It is shown that, for an uncontrolled breakdown where the local field strength is not carefully matched to the instantaneous plasma condition to avoid strong reflections, the heating effect will be self limiting and the resultant shock strength depends only on the incident wave frequency and on the initial gas density. A numerical example for microwave breakdown in air indicates that, at normal sea level density, the shock wave accompanying the breakdown is generally quite weak (of the order of Mach 1.1 at 100 Gc/sec frequency). However, for breakdown at lower air densities, stronger shock waves can be anticipated. Preliminary experimental observations of pressure waves generated in a one‐dimensional channel by pulse microwave discharges tended to confirm the general features of the elementary theory but showed somewhat stronger effects than predicted.

ISSN:0031-9171    

DOI:10.1063/1.1710955

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Four examples of the exact solutions of two‐dimensional magnetohydrodynamics of incompressible inviscid fluid are given. Two are valid for infinite conductivity and the other two for finite conductivity.

ISSN:0031-9171    

DOI:10.1063/1.1710956

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Weymann's observation of a wave of electrons propagating from a strong shock into the region ahead of it is considered. By taking into account the mutual electrostatic repulsion of the electrons through a simple approximation, the main features of the precursor wave motion can be explained. In particular, the theory predicts the relatively gradual decrease in electron density from the shock to the electrostatic front, followed by exponential decay upstream from the electrostatic front.

ISSN:0031-9171    

DOI:10.1063/1.1710957

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The boundary layer in the weak pressure interaction region of a plane hypersonic flow over a thermally insulated surface is discussed.

ISSN:0031-9171    

DOI:10.1063/1.1710958

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The stability of a free laminar layer between parallel streams is examined. The neutral curve and the curves of constant amplification are obtained by a numerical method for Reynolds numbers ranging from 0 to 40 as well as for the inviscid case. No minimum Reynolds number is found. The eigenfunctions are discussed. The case of a layer of increasing thickness is considered, and it is concluded that turbulent transition will occur when the Reynolds number reaches 150.

ISSN:0031-9171    

DOI:10.1063/1.1710959

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The investigation is concerned with motions in the region of the core of a vortex which exhibit peripheral vorticity. From theoretical reasoning it appears that development of such motions is favored as a zonal maximum of axially vorticity components is produced, e.g., by divergence of the vortex core. Several experiments devised to verify theoretical conclusions furnish evidence that concentrations of vorticity periodic about the perimeter actually do occur as expected.

ISSN:0031-9171    

DOI:10.1063/1.1710960

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The velocity of a fluid mass imbedded in another fluid, which is of a different viscosity and a different specific weight and flowing in a porous medium under a prevailing uniform pressure gradient, is investigated. The fluid mass may take the form of a circular or elliptic cylinder, a sphere, or an ellipsoid, and the orientation of the fluid mass, if not spherical, is completely arbitrary with respect to both the direction of the pressure gradient and that of gravity. Exact closed solutions are obtained. The results for two‐dimensional flows are applicable to Hele‐Shaw cells.

ISSN:0031-9171    

DOI:10.1063/1.1710961

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The entropy increases arising from chemical nonequilibrium in inviscid flows are investigated by the use of an analytical model. After the validity of the model is examined, the irreversibilities in nonequilibrium expansions are studied. The basic approach to the problem is an analytical study of limiting behavior of the entropy integral followed by numerical evaluation of this integral over finite limits. Small perturbation analyses are employed for investigating near‐equilibrium and near‐frozen flow in order to justify truncation of the entropy integral for some cases. The conditions necessary for the existence of freezing and for the existence of entropy bounds are established for large expansions. The results of exact numerical solutions for nonequilibrium nozzle flows are compared with those from isothermal approximations for upper bounds on entropy increments. Irreversibilities are also evaluated for relaxation flows in a constant‐area duct, a shock‐wave reaction zone, and a venturi for a previously frozen flow. It is observed that the entropy rise in the freezing process is practically negligible compared with the total entropy for a wide range of conditions characterizing flows of technical interest. The constant‐area relaxation and venturi relaxation flows also show small entropy rises. The shock wave and its accompanying relaxation zone lead to substantial irreversibilities. The entropy rise in the expansion cases is small permitting constant entropy approximations which may be utilized in numerical computation.

ISSN:0031-9171    

DOI:10.1063/1.1710962

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The energy and momentum relaxation of a nonequipartition gas mixture is considered. It is assumed that each component of the mixture has a Maxwellian distribution at a temperatureTi, with the peculiar velocity of the Maxwellian measured relative to the mean velocity of theith species. For the case in which a ``diffusion'' Mach number is not too large, the results have a particularly simple form. The calculations were carried out for the hard sphere, Coulomb, and Maxwell force laws of interaction. It is also noted how these results may be used to construct kinetic model equations for the case of hard sphere and Coulomb interaction, in a manner similar to that proposed by Sirovich.

ISSN:0031-9171    

DOI:10.1063/1.1710963

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Solutions of the linearized Boltzmann equation which may be found from finite moment equations are studied. A general solution to this problem is found and its properties discussed. A more restrictive class of such solutions, called generalized normal solutions, are then uncovered. These constitute a wide class of solutions in any desired number of moments. The governing equations are rendered determinate by exact expressions relating higher moments to the distinguished moments. In certain circumstances the initial data must be altered, and the resulting ``ersatz'' initial data used in connection with the equations. A case in point is the usual normal solution of the Hilbert‐Chapman‐Enskog theory. The ``ersatz'' initial data then renders the latter into an exact asymptotic theory. In addition higher moment systems are discussed in detail. It is shown that the generalized normal solutions are by no means a comprehensive class. Exact solutions of the Boltzmann equation which are also exact solutions of the Euler equations, the Navier‐Stokes equations, the Burnett equations, the Thirteen moments equations (among others) are exhibited. Furthermore, these can satisfy the Boltzmann equation in an infinite variety of ways.

ISSN:0031-9171    

DOI:10.1063/1.1710964

出版商:AIP    

年代:1963

数据来源: AIP