摘要:

The stability of a viscous fluid between two concentric cylinders with an axial flow is investigated for the case in which the azimuthal velocity is the sum of a velocity distribution due to the rotation of the cylinders and a “pumping” velocity distribution due to the pressure gradient acting round the cylinders. The outer cylinder is stationary and the spacing between the cylinders is assumed small. For various small Reynolds numbers associated with the axial flow the Taylor number is computed for a large range of values of the ratio of the average pumping velocity to the average velocity of the rotation.

ISSN:0031-9171    

DOI:10.1063/1.1694390

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The Be´nard problem of the radiating nongray fluids is examined in terms of the Eddington approximation. The nongrayness of radiation is prescribed by the ratio and product of the Planck and Rosseland means of the absorption coefficient,&eegr; = (&agr;P/&agr;R)1/2and&agr;M = (&agr;P&agr;R)1/2, respectively. Effects of radiation on the classical problem are then characterized by four parameters: the Planck number,P0(the ratio of conduction to radiation), optical thickness,&tgr; = &agr;Md(dbeing the distance between the plates) nongrayness of the fluid&eegr;and the emissivity of boundaries&egr;0and&egr;1, respectively. The radiation in general has a stabilizing effect; decreasingP0, increasing degree of nongrayness for&eegr; > 1, changing color of boundaries from black to mirror all delay the onset of instability. The boundary color and nongrayness of gas are responsible for the extrema observed in stability curves. Accuracy of the Eddington approximation is checked with the exact solution and the convergence of the approximate solution is studied in terms of the first and second approximations. Results are given for black‐black, mirror‐mirror, and black‐mirror boundaries.

ISSN:0031-9171    

DOI:10.1063/1.1694391

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The buoyancy driven thermal stability of a radiating nongray gas between two infinitely long vertical plates is studied analytically. The Squire theorem is shown to hold, and two‐dimensional disturbances are more dangerous than the corresponding three‐dimensional ones. A combination of the Galerkin and Chandrasekhar methods are used to solve the eigenvalue problem associated with two‐dimensional disturbances. In contrast to the Benard problem, the effect of radiation on the onset of stationary cells diminishes as the optical thickness of the gas increases indefinitely.

ISSN:0031-9171    

DOI:10.1063/1.1694392

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A numerical solution of the Boltzmann equation with the Bhatnagar‐Gross‐Krook model is obtained for Poiseuille flow and thermal creep of a rarefied gas between two parallel plates. The numerical results of Poiseuille flow are in fair agreement wth the experimental data of Dong and predict the Knudsen minimum in volume flow rate. The present results of the thermal creep approach a thermal transpiration formula analyzed on the basis of the elementary kinetic theory of gases as the density of the gas decreases and agree well with Maxwell's equation continuum theory in the range of low Knudsen number. The effect of the thermal creep on the velocity profile of Poiseuille flow is very large, especially at the Knudsen layer near the plate.

ISSN:0031-9171    

DOI:10.1063/1.1694393

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A method to interpret properly surface measurements near the leading edge of sharp slender bodies in hypersonic flow is described. The results, using a two‐sided Maxwellian distribution function at the surface, are used to relate: (a) the surface molecular flux,&PHgr;, topc, the pressure in a cavity connected through a sharp lipped orifice to the surface, and (b) the surface normal stress,pyy, topcand either (method 1) the surface number density or (method 2) the surface heat transfer and shear stress. Attention is drawn to the importance of the correct treatment of normal momentum accommodation coefficient, angle of attack, and orifice geometry. The present method is compared with others in whichpy yis obtained frompcand while it agrees with them in the continuum and slip regimes, it is the only method to agree with the correct free‐molecular flow limit. Flat plate pressure measurements, although made through tubes rather than sharp lipped orifices, are reviewed. Despite the attendant errors, which have been confirmed by very recent work, the following conclusions are drawn. (i) Results from methods (1) and (2) are consistent. (ii) Previous calculations ofpy yare in error by up to a factor of three when the shear stress is finite. (iii)py ynear the leading edge approaches somewhere near the free molecular limit.

ISSN:0031-9171    

DOI:10.1063/1.1694394

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The problem of power‐law recompression of a fully developed centered one‐dimensional expansion is examined for the case of&ggr; = 3. Two closed‐form integrals based on the similarity theory are derived. A physical picture based on finite‐amplitude traveling waves is developed. Explicit formulas for the flow distributions in the recompression layer are obtained for the power exponent values of 4/3, 3/2, 2, 3, and 4. Applications to problems in one‐dimensional unsteady release and two‐dimensional steady escape of detonation products are noted.

ISSN:0031-9171    

DOI:10.1063/1.1694395

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The electrical conductivity, translational and reactive thermal conductivity and viscosity have been computed for ionized argon in thermodynamic equilibrium at pressues from 0.001‐1000 atm and temperatures to 35 000°K. Comparison of the values with experiments shows reasonable agreement.

ISSN:0031-9171    

DOI:10.1063/1.1694396

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Measurements of electron density behind a shock wave in air are presented. Operating conditions are such that shock‐wave deceleration, boundary‐layer mass loss, and chemical nonequilibrium are important in the determination of the development of the electron density behind the shock wave. A one‐dimensional unsteady analysis is described. Calculated electron density is compared with experimental values. Agreement is within a factor of 2. The difference is probably attributable to expansion waves embedded in the test gas.

ISSN:0031-9171    

DOI:10.1063/1.1694397

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A new type of electrostatic probe design is proposed, which should permit temperature and density measurements for both ions and electrons from the accelerated current regions of the probe characteristics. Ion temperature measurements, in particular, have been difficult to obtain using standard probe techniques. The method is based on the use of one of a family of nonspherical probe geometries which can be operated as if they were spheres collecting orbit‐limited current. One such probe is a proposed multi‐electrode system having the advantage that the collector can be made much smaller than the usual spherical probe. The simultaneous use of this probe with a standard orbit‐limited cylindrical probe would then enable the above measurements to be made. The multi‐electrode probe may itself function as an orbit‐limited collector of both the spherical and cylindrical types, with different bias strategies on its electrodes for the two cases. The proposed probe operation is theoretically justified by rederiving the usual orbit‐limited current expressions for spheres and circular cylinders, without making any assumption regarding particle angular momentum conservation. The expressions are thereby shown to apply to a wider variety of probe shapes, including: (a) any convex cylinder, (b) any “sufficiently convex” three‐dimensional collector (for example prolate and oblate spheroids having major to minor axis ratios up to 1.653 and 2.537, respectively), and (c) the proposed multi‐electrode design. Some aspects of probe use in flowing plasmas and in magnetic fields are also discussed.

ISSN:0031-9171    

DOI:10.1063/1.1694398

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The photoionization chamber consists of a test gas which is bounded by parallel plates and ionized to a small extent by incident radiation. The charged particles formed by the ionization process diffuse to the walls of the chamber where they recombine. The particle densities and electric field distributions as well as the current‐voltage characteristic are studied. At low levels of ionization the electron density is neglected with respect to the ion density. By coupling this simplification with correct scaling, it is possible to obtain analytic solutions. The resulting current‐voltage characteristic reflects the rate of ionization as well as the ratio of the ion to the electron temperature. When this ratio is equal to unity, the ion and electron current fluxes saturate at the same rate. If this ratio is less than unity, the electron current flux saturates more slowly than the ion current flux. At higher levels of ionization the electron density can no longer be neglected with respect to the ion density and the problem is solved numerically. The current‐voltage characteristic obtained in this case can be approximated analytically at small and large voltages. The expression which applies to small voltages agrees with the results of other double probe studies.

ISSN:0031-9171    

DOI:10.1063/1.1694399

出版商:AIP    

年代:1973

数据来源: AIP