摘要:

Several approximate solutions of the Boltzmann equation for shock waves are shown to be applications of the method of weighted residuals. Values of shock thicknesses obtained by these methods are compared, and a systematic procedure for improving the accuracy of the general method is suggested.

ISSN:0031-9171    

DOI:10.1063/1.1694273

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

It is shown that the distribution function assumed by Mott‐Smith determines a unique relation between heat flux, stress, and fluid velocity given byq = (3/2)&tgr;u, i.e., it provides a constitutive relation for heat flux, and it also determines a simple expression for the ratio of third‐order central momentsQ = ⟨C x3 ⟩ / ⟨C x C 2⟩. These expressions allow the equation of transfer forcx2to be cast in a form that yields a nonlinear constitutive relation for stress. The results obtained from the Mott‐Smith ansatz are compared with the theory of Baganoff and Nathenson and results from a numerical solution of the Boltzmann equation for shock‐wave structure obtained by Hicks and Yen.

ISSN:0031-9171    

DOI:10.1063/1.1694274

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Elementary solutions of the coupled pair of integrodifferential equations arising from the decomposition of the linearized BGK equation in the kinetic theory of gases are used to solve the problem of heat transfer between parallel plates with arbitrary surface accommodation. A coupled pair of Fredholm equations is derived, and rapidly convergent iterative solutions are constructed. These solutions are then used to obtain accurate values of the heat flux between the plates and the temperature and density profiles, for various values of the accommodation coefficient and inverse Knudsen number. Numerical results for the heat flux are presented and compared to existing variational solutions. Also, explicit results for the temperature and density profiles are given.

ISSN:0031-9171    

DOI:10.1063/1.1694275

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Analytical and numerical calculations are carried out for an initially adiabatic blast wave in which the effect of transparent gas radiation increases as the temperature decreases. After a radiative cooling time is reached, a very dense shell of gas rapidly forms behind the shock front, and a cooling wave slowly progresses through the hot interior gas. The cooling wave reduces the interior pressure, resulting in an attenuation of the shock‐front velocity. For a specific heat ratio&ggr;near unity the shock velocity will remain near the adiabatic value, whereas for&ggr; = 5/3the shock velocity will approach the value for a momentum‐conserving shell, as predicted by some authors.

ISSN:0031-9171    

DOI:10.1063/1.1694276

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

This theoretical study investigates the influence of (1) the nonequilibrium excited state population in the relaxation region and (2) line radiation in the precursor on shock wave structure by considering strong shock waves propagating at Mach 18 and 24 into a theoretical argon‐like gas at a pressure of 1 cm Hg and a temperature of 300 °K. The argon atom is modeled as having two bound states plus a continuum, and the calculations include finite atom‐atom and electron‐atom collisional ionization and excitation rates as well as continuum and line radiation. The electron gas is allowed to be at a different temperature from the atom gas; consequently, three types of of nonequilibrium exist: ionization, excitation, and thermal. In the collisional relaxation region, which serves as a source of radiation to create the precursor, the degrees of ionization and excitation generally lag behind their respective local equilibrium values. By doing so they greatly influence the emission of radiation. The line wing radiation increases the extent of the precursor compared with former studies which considered only continuum radiation. However, elimination of the assumption that the excited states are in equilibrium with the electrons at the electron temperature decreases the magnitude of the precursor compared with results where the assumption has been used because the radiative flux is reduced.

ISSN:0031-9171    

DOI:10.1063/1.1694277

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Measurements have been carried out of the current, electric field strength, and radial temperature distribution in a 5 mm diam. wall‐stabilized electric arc in argon at pressures from 1‐200 atm. These data have been analyzed to determine the electrical conductivity as a function of temperature and pressure. The results are in reasonable accord with other measurements to 10 atm and with theory.

ISSN:0031-9171    

DOI:10.1063/1.1694278

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A revision of the electrostatic gas breakdown wave apparatus used by Haberstich and Winn has been employed to generate waves for studies of wave speed, and electron temperature and density behind the wave front. The measurements were carried out in helium at applied electrode voltages from 6 to 42 kV of both polarities and over a pressure range of 0.3 to 30.0 Torr. Nuclear data‐handling techniques were adapted to the measurement of the wave speeds to increase the accuracy of the data. Good over‐all agreememt is obtained with the theory of Shelton.

ISSN:0031-9171    

DOI:10.1063/1.1694279

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The stability of the axisymmetric modes of a viscous flow of an annular cylindrical layer of fluid carrying an electric current is considered in the presence of an independent parallel electric current along the axis. Even if the electrical conductivity of the fluid is small, sufficiently strong steady‐state flow with a radial velocity gradient can reduce the growth rates so much that thee‐folding times of the instabilities is larger than the time of flow over a typical length.

ISSN:0031-9171    

DOI:10.1063/1.1694280

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The results of an experimental demonstration of electromagnetic detonation waves are presented. These waves are obtained by discharging a capacitor bank across the annulus of a magnetic annular shock tube filled with hydrogen‐oxygen mixtures. Wave speeds of more than twice the usual steady Chapman‐Jouguet detonation speeds are observed. Experiments with argon in place of the combustible mixture were also conducted to illustrate the basic difference between electromagnetic shock waves and electromagnetic detonations. Theoretically calculated results are included to provide a better understanding of the observed experimental results. It is suggested that techniques similar to those used in these experiments may be used to produce high‐speed detonations for gasdynamic laser applications or to stabilize combustion waves in a supersonic stream.

ISSN:0031-9171    

DOI:10.1063/1.1694281

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Strong laminar electrostatic shock waves have been experimentally observed when an ion beam is injected into a collisionless plasma. The structure of the shock is qualitatively different from one with a trailing wave train. A density depression follows behind the shock front, and no trailing wave train due to wave dispersion is found. A significant amount of ions reflected from and transmitted through the shock front form a precursor. The critical Mach number above which no shock is formed is found to be 1.5. Numerical simulations reported here reproduce the experimental observations very well. An analysis based on the water‐bag model accounts for the observed value of the critical ion‐beam velocity which gives the critical Mach number. It also points out that the reflected ions play an essential role in the persistence of the shock.

ISSN:0031-9171    

DOI:10.1063/1.1694282

出版商:AIP    

年代:1973

数据来源: AIP