摘要:

A similarity solution is developed describing the propagation of a strong cylindrical shock in an applied azimuthal magnetic field. The stationary gas is nonconductive and the shocked gas is taken to have a finite electrical conductivity. The total axial current is maintained constant by external means. Upon comparison of flows for which the total gas energy is the same, it is found that the interaction reduces the shock velocity by only a few percent although the pressure distributions differ markedly.

ISSN:0031-9171    

DOI:10.1063/1.1706608

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The effect of small unsteady mass, momentum, and heat addition in a uniform (or piecewise uniform) basic flow is discussed. A general solution is given. A method for obtaining closed‐form solutions, in cases where the disturbed flow is self‐similar, is also presented. These solutions are applied to find the interaction between a flow, due to a piston starting impulsively from rest, and a transverse magnetic field. It is assumed thatRm« 1 andRmRh« 1, whereRmandRhare the flow magnetic Reynolds and pressure numbers, respectively. The electrical potential is assumed to be uniform in the channel. Both a narrow (in the streamwise direction) intense magnetic field and a wide, less intense, field are treated. In the latter case it is found that the shock, generated by the motion of the piston, is decelerated by the magnetic field when the shock Mach numberMsis near 1 but is accelerated by the magnetic field whenMsis high. This behavior is due to the electromagnetic body forces dominating atMsnear 1 and the Joule heating dominating at largeMs. These numerical results also apply to the hot‐gas region of a shock tube employing strong shocks.

ISSN:0031-9171    

DOI:10.1063/1.1706609

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A new technique for measuring the thermal conductivity of gases over a fairly wide temperature range is described. The method makes use of precise measurements of the thermal‐wake widths downstream of a steady line source of heat in a uniform laminar flow of the test gas. The theory and practice of the method are discussed, and it is shown to have advantages over conventional methods in that it is an absolute technique requiring measurement only of distance, gas velocity, and relative temperature differences. The technique has been tested on N2and CO2over the range 300–1100°K with results that agree well with previously reported work done by conventional means. Measurements on N2‐CO2mixtures covering the entire composition range and in the same temperature interval are also presented. These are compared with kinetic‐theory calculations using the best available input data. The results are then used to predict the thermal conductivity of N2, CO2, and N2‐CO2mixtures up to 2000°K with what is believed to be the most reliability which is presently possible.

ISSN:0031-9171    

DOI:10.1063/1.1706610

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A full‐range moment method developed by Lees is applied to heat transfer across a large temperature difference in a rarefied gas. Two solutions are obtained: a four‐moment result for hardsphere molecules and a six‐moment result for Maxwellian molecules. The four‐moment solution for hard spheres exhibits the same behavior as Lees' result for Maxwellian molecules. Moreover, the six‐moment result differs significantly from the lower‐order solution for Maxwellian molecules only in the prediction of a varying pressure.

ISSN:0031-9171    

DOI:10.1063/1.1706611

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

An experimental investigation of low‐speed pipe flow was conducted for an initially turbulent flow of air. At subcritical Reynolds numbers, as the fluid traveled downstream its velocity profile approached the parabolic distribution corresponding to laminar flow; the rate of transition toward laminar flow being more rapid at lower Reynolds numbers. Concurrent hot‐wire‐anemometer measurements showed a corresponding dependence on Reynolds number of the rate of decay of the longitudinal velocity fluctuations. These velocity fluctuations were also found to decay more rapidly near the wall and center of the pipe than at intermediate radii. The energy spectrum of the fluctuations was measured along the pipe centerline, and, in terms of the macroscale, these spectra were similar.

ISSN:0031-9171    

DOI:10.1063/1.1706612

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The radiation emitted by hot nitrogen behind normal shocks is studied at an equilibrium temperature from 6000° to 6800°K and densities from 0.01 to 0.20 atm. The various radiating bands are identified by spectroscopic and photometric techniques. The radiation is found to consist of bands from the N2+(1−), N2(1+), and N2(2+) systems. The radiative relaxation of the N2(1+) system in the nonequilibrium region is studied at various densities and shock speeds and is used to determine the recombination rate constants,kRNandkRN2for the reactions N + N + N → N2+ N and N + N + N2→ N2+ N2, respectively.kRNis found to be 1.8 × 10−32± 0.6 cm6/sec at 6400°K andkRN2to be at least 13 times smaller thankRN. Comparison is made between theoretical calculations based on these rates and observations. The integral nonequilibrium radiation and the time of occurrence of peak radiation behind the shock front are also examined.

ISSN:0031-9171    

DOI:10.1063/1.1706613

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

An experiment is reported in which an induced Hall electromagnetic force in air is measured in a shock tube. Agreement is found with theory for values of the product of the electron cyclotron frequency and the mean collision time for electrons over a gas temperature range of 3000° to 4200°K. The theory is based upon a mean collision time for electrons that is determined solely by electron‐neutral particle collisions, and an Ohm's law that is valid for slightly ionized gases. The induced Hall electromagnetic force is theoretically independent of the electron concentration of the shock‐heated air. The experiment thus provides a technique for determining the collision time that does not depend upon the establishment of equilibrium. Details of the time profile of the measured emf are explained qualitatively using an equivalent circuit.

ISSN:0031-9171    

DOI:10.1063/1.1706614

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Numerical calculations are made of a strong one‐dimensional disturbance traveling perpendicular to a magnetic field in a fully ionized and collisionless plasma. When the Alfve´n‐Mach numberMhis greater than 2, orbit crossings of the ions occur, which rapidly leads to thermalization perpendicular to the magnetic field if the crossings are extensive (Mh> 3). The thermalization approximates the behavior of a classical hydromagnetic shock, with a shock‐front thickness roughly equal to the distance the shock front travels in one‐half an ion gyration time. This length is somewhat greater than the ion gyration radius. The structure of the front is found to be strongly time dependent, and undergoes large fluctuations in an ion gyration period. It is argued that when the ion‐electron mass is large, the magnetic forces tend to suppress electron orbit crossings. This results in relatively cold electrons in the shocked region, with the ions obtaining nearly all of the thermal energy. A relationship between the longitudinal electrostatic potential difference across the shock front and mass flow in the plane of the front is derived on the basis of a simplified model and is found to be in qualitative agreement with the numerical results. The range of applicability of the calculations to real plasmas is discussed.

ISSN:0031-9171    

DOI:10.1063/1.1706615

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A technique due to Dupree is used to investigate the pair correlation function in a dilute, uniform, quiescent plasma. It is demonstrated that his formal expression for the pair function may be evaluated in many cases of physical interest. In equilibrium one obtains the usual Debye‐Hu¨ckel result, which may be generalized to the case of a plasma having different temperatures in different directions. A Lorentzian‐type velocity distribution gives rise to a correlation function containing less than unit screening charge. It is shown that such behavior is only to be expected for velocity distributions that approach zero rather slowly in the limit of large velocity. Finally, a Druyvesteyn‐type distribution is investigated and shown to lead to a pair function that falls off somewhat more slowly, and has a different form, from that of the Debye‐Hu¨ckel theory.

ISSN:0031-9171    

DOI:10.1063/1.1706616

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Previous derivations of the kinetic equation for a completely ionized gas have proceeded under the following assumptions: (a) the system is spatially uniform, and (b) sufficient time has elapsed so that the higher distribution functions depend on time only through the one‐particle distribution. A kinetic equation is derived which is not subject to these restrictions, and is valid for any system not too far from equilibrium.

ISSN:0031-9171    

DOI:10.1063/1.1706617

出版商:AIP    

年代:1962

数据来源: AIP