摘要:

Local boiling, cavitation, and cavitation collapse have been observed in the heat induced counter‐flow of He II in a convergent‐divergent nozzle. These observations are described and shown to be qualitatively and quantitatively in agreement with the two fluid equations supplemented by the Gorter‐Mellink force.

ISSN:0031-9171    

DOI:10.1063/1.1692707

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Theoretical and experimental investigations have been made for the problem of a source or sink at the axis of a viscous, incompressible, steady, unbounded rotating fluid. For the sake of generality, the theoretical portion of this paper also includes a uniform axial velocity. It is found that the velocity distributions have similarity forms at the distant wake along the axis of rotation using the Fourier transform technique. An inverse coordinate expansion technique is then used. This procedure not only brings out the nature of the approximation very clearly but also allows higher‐order solutions to be calculated. The zeroth‐order solution indicates that there exists a withdrawal viscous core which grows in radius with the axial distancex*from the sink at the ratex*1/3. The first‐order solutions are also calculated. The experimental results agree very well with the theoretical predictions.

ISSN:0031-9171    

DOI:10.1063/1.1692708

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A universal criterion for the stability under arbitrary disturbances of the convective flow of a fluid in a porous medium is obtained in terms of a Reynolds number and a Rayleigh number for the flow. It is also shown that stability bounds obtained by small perturbation methods are equally good bounds under arbitrary disturbances.

ISSN:0031-9171    

DOI:10.1063/1.1692709

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The model neutral exosphere of O¨pik and Singer for a nonrotating planet is generalized by permitting the corresponding barosphere to rotate uniformly at an angular velocity which may or may not be equal to that of the planet. For this case the velocity‐distribution function, satisfying the collisionless Boltzmann equation, is constructed. Then, the density is determined from the distribution and compared with the corresponding result for a nonrotating planet obtained by O¨pik and Singer. In addition, the radial and azimuthal fluxes are derived. Based on the result for the azimuthal flux, the point at which exospheric corotation can be said to have broken down is indicated for several conditions. It is shown that in all cases, for a given radius, the density at the equator exceeds the density at the pole. For example, a model terrestrial neutral exosphere of hydrogen, helium, and oxygen has density ratios between the pole and the equator of 0.984, 0.869, and 0.530, respectively, atr = 2R.

ISSN:0031-9171    

DOI:10.1063/1.1692710

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The hydrodynamic limit of the Enskog equation for one‐dimensional hard cores is solved in general, and for the special cases of sound and shock propagation. This equation is shown to be the limit of the exact microscopic kinetics, which is also solved exactly.

ISSN:0031-9171    

DOI:10.1063/1.1692711

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

In the asymptotic evaluation of certain integrals in the method of Kahn and Mintzer describing high‐frequency sound propagation, certain errors occur. These have been described and corrected in an attempt to obtain a valid description of sound dispersion and attenuation over a wide range of frequencies. However, the corrected asymptotic results fail to yield physically acceptable modes of propagation for all values of the rarefaction parameter&tgr; = p/&ohgr;&mgr;. Only for small values of the rarefraction parameter (the high‐frequency limit) are suitable descriptions of experimental results obtainable. The physical and mathematical reasons for the failure of free molecule expansion polynomials to predict continuum sound modes are discussed.

ISSN:0031-9171    

DOI:10.1063/1.1692712

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

In the case of steady flow out of an orifice into an originally evacuated half‐space, a method is given for obtaining the first correction to free flow for the net outflow through the orifice for the class of collision functionsB(&thgr;, V)cut off or made regular near&thgr; = &pgr;/2. An explicit computation is described for hard‐sphere molecules and the resultant fractional correction is1 + 0.145/KwhereKis the Knudsen number. The coefficient 0.145 is about 30% lower than the current best data for argon.

ISSN:0031-9171    

DOI:10.1063/1.1692713

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The first two terms of the Cameron‐Martin‐Wiener representation for turbulence are employed to examine the expected characteristics of the Burgers' model equation for initial‐value problems. The representation employs the basic white noise process, nontime varying, and the characteristics of the expansion at later time are found. The equations are integrated more completely than in earlier works, and it is seen that so long as the initial spectra are not too far from equilibrium spectra the representation is adequate to a couple of correlation times. For greater time it would be necessary to employ higher‐order terms or to turn to time‐dependent white noise processes in the expansion. It is shown that it is possible to use a single white noise process to examineequilibriumcharacteristics for the model turbulence. Without further approximation, the by now familiar energy spectrum is derived,E ∼ k−2. Other recent work relating to the Cameron‐Martin‐Wiener expansion is reviewed critically.

ISSN:0031-9171    

DOI:10.1063/1.1692714

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A model for statistically isotropic homogeneous turbulence in an incompressible fluid is constructed, representing the turbulence as a superposition of individual vortex sheets. Each vortex sheet moves in the velocity field of the other sheets which have larger scale. Each sheet is stretched out, and intensified, until obliterated by viscosity at high wavenumber. The rate of stretching is related to the symmetric part of the strain tensor∂&ngr;i/∂&kgr;j, which is postulated to be statistically independent of the antisymmetric part. Representing the turbulence by the usual energy spectrum functionF(k)leads to a set of integrodifferential equations. Solution of the equations gives a spectrum which is in close agreement with experimental spectra of turbulence over both the inertial and viscous subranges, suggesting that the model may be of some real physical interest. The model is sufficiently explicit so as to give information on the correlation between different Fourier components of the turbulence. The calculations give the probability of finding a particular value of the vorticity or velocity at a given position and time in the turbulent field.

ISSN:0031-9171    

DOI:10.1063/1.1692715

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The investigations of this study are concerned with: (1) the physical processes that occur in the precursor and in the nonequilibrium region behind a strong shock wave during its approach to equilibrium in an argonlike gas; (2) the influence of different atom‐atom collisional rates in the relaxation region on the precursor; and (3) the cause of precursor ionization, which in this study has been assumed to be the photoionization of both the ground and excited states. The argonlike gas is regarded as a combination of two gases; one consisting of electrons and the other of atoms and ions. Temperature differences between the two gases affect both the approach to equilibrium behind the shock wave and the precursor. Just behind the shock wave, the electron gas is cold relative to the atom gas. Farther into the relaxation region, the electron temperature approaches that of the atom gas, and thermal equilibrium is reached. Shortly thereafter, ionizational equilibrium is reached, and the gas begins to cool by the emission of excited‐state radiation until it reaches its final steady state. The precursor ionization depends directly on the ratio of radiative to convective energy; thus, decreasing the ambient pressure increases both the extent and magnitude of the precursor. Increasing the atom‐atom cross section increases the precursor ionization; however, changing the atom‐atom cross section does not affect the extent of the precursor.

ISSN:0031-9171    

DOI:10.1063/1.1692716

出版商:AIP    

年代:1969

数据来源: AIP