摘要:

The optical reflectivity method was used to investigate the structure of shock fronts in argon from Mach 1.70 to Mach 4.85 and in nitrogen from Mach 2.01 to Mach 3.72. Experimental data were obtained at two wavelengths and over a wide range of initial pressures. The reflectivities, corrected empirically for shock curvature, were fitted to a bimodal profile to yield a maximum‐slope density thickness. The reciprocal of the thickness in argon (expressed in terms of the Maxwellian mean free path in the undisturbed gas) rises rapidly to a maximum of approximately 0.31 at about Mach 3.5 and decreases gradually thereafter. Above Mach 3 the thickness is about 50% greater than calculated from the Navier‐Stokes equations, using a realistic viscosity‐temperature relationship. There is excellent agreement, especially at the higher shock strengths, with recent bimodal calculations carried out by Muckenfuss, using realistic intermolecular potentials. In nitrogen, the shocks are thinner than in argon and appear to attain a minimum value of 2.5 initial mean free paths at about Mach 3.7. Rotational relaxation appears to be as rapid in the strong shocks as previously observed in weak shocks; it appears to be completed within the shock front. The experimental density thicknesses are approximately 50% greater than those calculated from the Navier‐Stokes equations, using the experimental shear viscosity &mgr; and a bulk viscosity of 2&mgr;/3. The agreement with these Navier‐Stokes solutions is about as good as those in argon.

ISSN:0031-9171    

DOI:10.1063/1.1711007

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The classical Navier‐Stokes theory was used to calculate profiles of plane shock waves in argon. The viscosity‐temperature relationship employed in the calculation was based on a Lennard‐Jones 6–12 intermolecular potential function for which the parameters were derived from experimental viscosity measurements up to 1100°K. With this viscosity function, the maximum‐slope shock thicknesses obtained were smaller than previously calculated assuming viscosity proportional toT0.816. Also it was found that the maximum‐slope thickness based on the density profile was less than that based on the velocity profile. The density profile thicknesses calculated with the Lennard‐Jones viscosity function were the same order of magnitude as, but not in quantitative agreement with experimental density thicknesses obtained with the optical reflectivity technique. It was found that Navier‐Stokes profiles become asymmetric as the shock strength is increased. However, the calculated asymmetry would have a negligible effect on thickness measurements by the optical reflectivity method.

ISSN:0031-9171    

DOI:10.1063/1.1711008

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The dimensionless ratiof = &lgr;M/&eegr;Cvrelating the thermal conductivity, molecular weight, viscosity, and constant volume molar heat capacity has been determined for several nonpolar polyatomic gases in the neighborhood of room temperature (270°–295° K). The experimental method, due to Eckert and Irvine, provides a direct determination offby measurement of the subsonic temperature recovery factor. A recent theory of Mason and Monchick has been used to calculate collision numbers for rotational relaxation from the experimental data as follows: CH4, 9.4; CF4, 3.0; SF6, 2.5; C2H4, 2.4; C2H6, 4.0; O2, 12; N2, 7.3; CO2, 2.4; and C2H2, 1.8. Collision numbers for the near‐spherical molecules were in close accord with a classical theory for rough sphere molecules with attractive forces; ethylene, which deviates appreciably from spherical symmetry, exhibited a smaller collision number. The data on linear molecules were in qualitative agreement with a quantum treatment. In general, collision numbers for rotational relaxation are determined by the following factors: (1) The molecular mass distribution, (2) the strength of the intermolecular attractive forces, and (3) the molecular asymmetry.

ISSN:0031-9171    

DOI:10.1063/1.1711009

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A transverse magnetic field imposed on a radiating shock wave is shown to inhibit the smoothing tendency of radiation energy transfer, and to alter the conditions for the occurrence of a temperature overshoot. Necessary and sufficient conditions for the smoothing of shocks by the mechanism of radiation energy transfer acting alone are discussed and numerical results are derived for the case of no magnetic field. A possible experimental test is proposed.

ISSN:0031-9171    

DOI:10.1063/1.1711010

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A kinetic model of the final‐stage decay of grid‐produced turbulence is presented. Theoretical analysis leads to an inverse‐square energy decay law. The prediction has been confirmed by measurements in a low‐speed water channel. A replot of the Dryden‐Schubauer and Batchelor‐Townsend wind‐tunnel data also indicates better agreement with the present inverse‐square, rather than the52‐power decay law proposed by earlier investigators.

ISSN:0031-9171    

DOI:10.1063/1.1711011

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A kinetic equation for a plasma of electrons and infinite mass ions is derived which exhibits no divergences for any impact parameter. The basic expansion used is inn&lgr;D3, the number of particles in a Debye sphere. The collision operator has Boltzmann, Fokker‐Planck, and Lenard‐Balescu behavior in the appropriate impact parameter regimes.

ISSN:0031-9171    

DOI:10.1063/1.1711012

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The linearized equations governing the time dependence of the one‐particle distribution function and the two‐particle correlation function in a one‐component plasma which is slightly removed from thermal equilibrium are investigated in the plasma limit. The integral equation for the two‐particle correlation function is solved by the Wiener‐Hopf method. It is shown that a self‐consistent evolution of the one‐particle distribution function and the two‐particle correlation function is not prescribed by the theory unless lengths on the order of the distance of closest approach in a two‐body encounter are retained. The relation of the analysis to the conjecture by Bogoliubov concerning the time dependence of multiparticle distribution functions is discussed. In particular, it is shown that although modes corresponding to distances larger than the Debye length are very slowly damped they do not make an appreciable contribution to the kinetic equations.

ISSN:0031-9171    

DOI:10.1063/1.1711013

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

An exact kinetic equation for plasma and the electromagnetic field is derived. This equation describes the fluctuations of the fields and particle distributions. The solution is obtained by expanding in a parameter which characterizes the amplitude of these fluctuations. A systematic procedure is given for generating the solution to arbitrary order in the expansion. Some typical applications of the theory are presented. These include calculations of a collision integral, incoherent scattering, and bremsstrahlung emission and absorption.

ISSN:0031-9171    

DOI:10.1063/1.1711014

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The equilibrium configuration consists of a uniform particle beam of circular cross section and infinite extent streaming at highly relativistic velocity through a uniform, dense background plasma. The plasma is characterized by a scalar conductivity, and the beam is described by a collisionless Boltzmann equation in which a two mass approximation to the relativistic dynamics has been made. The stability problem for this configuration is formulated as a set of three linear, coupled integral equations for three field variables (certain Hankel transforms of the perturbed electric field), and a formal solution of the equations is obtained by iteration. The dispersion relation appears as a solvability condition. The treatment gives a full account of the betatron orbits of the beam particles. Asymptotic results are obtained for low‐frequency, long‐wavelength disturbances and for high‐frequency, highly localized disturbances.

ISSN:0031-9171    

DOI:10.1063/1.1711015

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A macroscopic analysis is given of the low‐frequency, long‐wavelength instabilities of the relativistic beam‐plasma configuration. A two mass approximation is used for the particle dynamics. Plasma effects are accounted for by means of a tensor conductivity whose nondiagonal elements are due to the self‐magnetic field of the beam. The analysis is directed toward establishing the effect of the nondiagonal terms on growth rates. Three approximate methods of analysis are discussed. The conclusion is that the nondiagonal terms, even when large, contribute minor modifications to the dispersion law.

ISSN:0031-9171    

DOI:10.1063/1.1711016

出版商:AIP    

年代:1963

数据来源: AIP