摘要:

An experimental and analytical study of nonequilibrium among the populations of the excited levels of potassium vapor passing through a supersonic nozzle is presented. In the experiment a small amount of potassium vapor was injected into a flow of a mixture of argon and helium, heated by an arc jet electric discharge to a temperature of approximately 2500°K at a pressure of 3 atm. The resulting plasma was passed through a supersonic nozzle (attaining Mach 2.2 at nozzle exit); the gas temperature dropped from 2500° to 1000°K in a time scale of 3 × 10−5sec. The electron temperature (though somewhat independent of the gas temperature) also decreased rapidly, causing the free electrons to recombine with ions of potassium. The recombined electrons passing through the energy level structure of potassium formed the basis of the electronic nonequilibrium. Spectrometric measurements (line intensity and line reversal) of the gas were performed upstream of the nozzle and at the nozzle exit. The electronic populations of expanded potassium vapor were observed to depart from equilibrium in qualitative accordance with theoretical predictions. Larger electron excitation cross sections (than the present theoretical ones) in the energy region near threshold would bring theoretical calculations of excited level populations and electron density at the nozzle exit into better agreement with measured values for these quantities.

ISSN:0031-9171    

DOI:10.1063/1.1694684

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The structures of the normal shock waves in weakly ionized nonequilibrium flows have been analyzed by the Krook kinetic models using the Maxwellian or the ellipsoidal distribution functions, and the calculated results were compared with those obtained from the bimodal approximations.

ISSN:0031-9171    

DOI:10.1063/1.1694685

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A method of determining the temperature of hot gases is described that is based on the measurement of the intensity of radiation on the center of an emission line. The line is selected on the basis that it possesses blackbody intensity at the central frequency and that its width is large compared with the available spectral resolution of the optical equipment. With these conditions fulfilled, no information on the specific properties of the spectral line is required to recover temperature. The method is applied to determine the temperature behind a shock‐wave propagating into xenon gas. The temperature of the shock‐heated gas is calculated by Rankine‐Hugoniot conditions based on the measured shock velocity. A comparison between measured and theoretical temperatures is presented, and it shows improved agreement at higher temperatures and pressures. The most serious limitation on the accuracy of our implementation of this experiment is considered to be the uncertainty of the shock velocity in the presence of moderate shock attenuation.

ISSN:0031-9171    

DOI:10.1063/1.1694686

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Linear theory is used to study the pure stagnation‐point flow created inside a rotating cylinder by introducing fluid uniformly through the top surface and removing it uniformly through the side wall. Of main interest is the completely new role played by theE1/2layer at the side wall, although the (unsteady)E1/4andE1/3layers also have novel features.

ISSN:0031-9171    

DOI:10.1063/1.1694687

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The Orr‐Sommerfeld equation is solved numerically for the boundary layer profiles which are the solutions to Stewartson's branch of the Falkner‐Skan equation. These profiles are of significance in describing post‐separation flows with negative skin friction. The cases considered are for the Hartree pressure gradient parameter&bgr; = −0.18, −0.15, −0.10, and −0.05. The profiles become more stable as&bgr;decreases from ‐0.05 to ‐0.18 in contrast to the results of the Falkner‐Skan similarity profiles with positive skin friction.

ISSN:0031-9171    

DOI:10.1063/1.1694688

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The Galerkin approximation technique is used to solve the flow problem of an infinite plate immersed in a non‐Newtonian power law fluid in the presence of a constant transverse magnetic field. The velocity outside the boundary layer depends exponentially on time.

ISSN:0031-9171    

DOI:10.1063/1.1694689

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A magneto‐fluid dynamic flow interaction in the shock tube flow of an electrically conducting test gas over a cone aligned with an applied magnetic field was experimentally observed, whereRM = 0.25. For the variable applied field up to 0.9 W/m2, the maximumIa = 0.50, andAvaried from greater than to less than unity. Gas dynamic flow changes were not observed, but the measured unsteady induced magnetic field data effectively illustrated the role of diffusion in the propagation of the fast and slow magnetoacoustic waves. In addition, the direct observation of the fast magnetoacoustic wave was a very significant result.

ISSN:0031-9171    

DOI:10.1063/1.1694690

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The collisional interaction of a test‐charged particle with a streaming Maxwellian distribution of field particles is considered analytically. Values are found for the collisional parameters of dynamical friction force, diffusion tensor, and rate of energy change for a wide range of field particle densities, temperatures, and streaming velocities. Retention of the velocity dependence of the Coulomb logarithm leads to substantial differences in the values of the parallel component of the diffusion tensor and the rate of energy change for the test particle as compared with the Spitzer values. Collision frequencies for momentum transfer,&pgr;/2angular deflection, and energy change for the test particle and the test plasma are defined, simply related to each other, compared with the Spitzer definitions and evaluated for a simple case. The new definitions for the collision frequencies place in evidence the enhancement of collisional momentum and energy transfer in the absence of stationary thermal equilibrium.

ISSN:0031-9171    

DOI:10.1063/1.1694691

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A previously derived Fokker‐Planck collision integral for an electron plasma in a dc magnetic field is examined in the limit in which the Debye length is greater than the thermal gyroradius, which is in turn greater than the mean distance of closest approach. It is demonstrated that the collision integral can be satisfactorily approximated by the classical Landau value (which ignores the presence of a dc magnetic field) if the following replacement is made: In the Coulomb logarithm, the Debye length is replaced by the gyroradius. This induces a fundamental logarithmic dependence on magnetic field in the relaxation times. Numerical comparison of the asymptotic approximations with the previously derived exact results is made, and good agreement is found. The simplification this introduces into the description of collision processes in magnetized plasmas is considerable.

ISSN:0031-9171    

DOI:10.1063/1.1694692

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The excitation of ion acoustic waves by nonlinear coupling of two transverse magnetic waves generated in a microwave cavity was investigated. Measurements of the wave amplitude showed good agreement with calculations based on the Vlasov equation.

ISSN:0031-9171    

DOI:10.1063/1.1694693

出版商:AIP    

年代:1974

数据来源: AIP