摘要:

A theory has been developed which gives the distribution of density with altitude for a planetary exosphere in the absence of local thermodynamic equilibrium. It gives values considerably lower than those conventionally calculated on the basis of the hydrostatic equation. Our results apply to the case where the field of force is gravitational; hence in the case of the earth, they give the density variation of only the neutral component of the exosphere.

ISSN:0031-9171    

DOI:10.1063/1.1705968

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The asymmetrical growth of an interface separating two fluids of different densities, under the influence of an imposed acceleration (Rayleigh‐Taylor instability), is shown to be mainly a nonlinear phenomenon. When the initial disturbance is a simple sinusoidal wave and is started from rest, it is found that the growth of the interface depends explicitly on two dimensionless parameters of the initial disturbance, namely, the dimensionless amplitude (i.e., the amplitude‐to‐wave‐length ratio) and the dimensionless wave number (i.e., the wave number of the initial disturbance to the ``cutoff'' wave number of the medium under the prevailing experimental condition). Results of the analysis show that the asymmetrical development of the interface occurs much earlier for disturbances of larger amplitudes and lower wave numbers than those of smaller amplitudes and higher wave numbers, i.e., those with wave numbers near the ``cutoff.'' Surface tension shows a definite stabilizing effect. Because of the nonlinear effect, for a sinusoidal initial disturbance, a generation of higher harmonics as well as a feed‐back to the fundamental is noted. Contrary to the prediction of the linearized theory, the present analysis, based on higher order approximations, reveals an ``over‐stable'' phenomenon for disturbances having initial wave numbers beyond the ``cutoff.''

ISSN:0031-9171    

DOI:10.1063/1.1705969

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Direct observation of the vortex pattern caused by a ring‐shaped trip is made on 1‐in. and ½‐in. circular cylinders and on a 30° cone in a water tank. Over the cylinders the boundary‐layer thickness is approximately equal to the radius of the cylinders. Ring‐shaped vortices are shed and deformed into vortex loops in the same manner as on a flat plate. On the cone the ring‐shaped vortices are stretched and then inevitably deformed into vortex loops, indicating that a mere stretching is not a sufficient mechanism for the creation of a turbulence spot. A mechanism of the final breakdown from the vortex loop is tentatively proposed.

ISSN:0031-9171    

DOI:10.1063/1.1705970

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Data are presented showing the properties of hypersonic boundary layers at Mach numbers from 8 to 10. The measurements extend experimental data on skin friction and heat transfer previously reported in the literature, and provide a basis for comparison with theory. Significant results of the investigation include the relatively rapid growth of the laminar sublayer at high Mach numbers, the increase in the momentum thickness with heat transfer, the decrease in the heat transfer coefficient, and the skin friction dependence on heat transfer and pressure gradient at high Mach numbers. The velocity profiles in the turbulent portion of the boundary layer are found to extend the trend evidenced at lower Mach numbers of a fit to a power profile, but with a somewhat lower velocity index (n= 5 as compared to 7 and 9 at lower supersonic Mach numbers). On the other hand an exponential fit to the experimental points provides equally good agreement, and satisfies better the physical conditions at the edge of the boundary layer.

ISSN:0031-9171    

DOI:10.1063/1.1705971

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

A centered simple wave is generated by the impulsive retraction of a piston. The sound speed perturbation and particle velocity perturbation are determined when the wave passes into a slowly diverging (or converging) section or a section which presents a throat. When the section of varying area terminates in a channel of constant cross section, the result of passage through the transition section of varying area is the superposition of a perturbation which tends to decrease the flow velocity by a term which varies inversely with the time for a point moving with the wave, but increases linearly with the time at a fixed point in the channel, in agreement with results first presented by Chester with the use of a two‐dimensional analysis. The flow of an arbitrary simple wave in the section of varying area is solved.

ISSN:0031-9171    

DOI:10.1063/1.1705972

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

An investigation is made of some modifications in the kinetic theory of gaseous transport properties which are necessary to take account of effects encountered at high temperatures. In particular, complications arise because of the existence of a multiplicity of different interaction energy curves governing collisions, and because of the possibility of resonant excitation and charge exchange during collisions. It is shown that the results of classical kinetic theory can be kept in the same form, but the cross sections or collision integrals have to be computed differently. It is pointed out that the present modifications are valid to all orders of Chapman‐Enskog approximation. It is also shown that excitation exchange is important in determining the transport properties of mixtures at high temperatures, and the method of calculation of the excitation exchange probability is extended to cases for which multiple interaction curves are involved.

ISSN:0031-9171    

DOI:10.1063/1.1705973

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The exponential potential function,Ae−r/&rgr;long has been regarded as the true qualitative form of the repulsive intermolecular potential at moderately small internuclear distances (or equivalently, high temperatures). Because of the increasing interest in gases at high temperatures it has become desirable to be able to evaluate the transport properties under these conditions. The calculation of integrals related to the usual collision integrals &OHgr;(l,s)and cross sectionsQ(l)have been carried out for the exponential repulsive potential. Some high‐temperature viscosities have been calculated and compared to the calculated results of Amdur and Mason which are based on an experimental scattering potential.

ISSN:0031-9171    

DOI:10.1063/1.1705974

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

A study is made of the flow of heat between parallel plates of slightly different temperatures. The problem is described by the linearized Boltzmann equation which is subject to microscopic boundary conditions. We approximate the distribution function by half‐range polynomials in velocity space and determine the space‐dependent coefficients by forming half‐range moment equations. An approximation involving four pairs of space functions suffices to give an accurate treatment of the heat flow and of the density and temperature profiles for the entire range of conditions from free molecule to hydrodynamic. Detailed numerical results for the temperature slip and molecular boundary structure are obtained for hard‐sphere molecules. The accuracy of cruder half‐range approximations and other methods of fixing the coefficients is established.

ISSN:0031-9171    

DOI:10.1063/1.1705975

出版商:AIP    

年代:1959

数据来源: AIP

ISSN:0031-9171    

DOI:10.1063/1.1705976

出版商:AIP    

年代:1959

数据来源: AIP

ISSN:0031-9171    

DOI:10.1063/1.1705978

出版商:AIP    

年代:1959

数据来源: AIP