摘要:

The measurement of pressure in He II with flowing superfluid superimposed in a stationary normal fluid was undertaken to demonstrate ideal fluid character of the superfluid below critical velocities. Quantitative agreement with Euler's equation with zero curl is shown with slip‐flow boundary conditions. Thus, Bernoulli's equation holds for potential flow and superfluid accelerations occur without dissipation. The method of pressure measurement demonstrates that net forces on an object in non‐uniform potential flow can be measured.

ISSN:0031-9171    

DOI:10.1063/1.1691939

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

For a fluid layer heated from below, a calculation is made of the nonlinear effect of surface curvature which turns out to be of the same type as the non‐Boussinesq effect. Results are given for the effects of variable fluid properties.

ISSN:0031-9171    

DOI:10.1063/1.1691940

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Fluid motion in a long straight channel induced by longitudinally varying surface tension has been discussed by Levich. This problem is re‐examined and a different solution is given. In addition, the stability of laminar flows involving surface‐tension variation is briefly discussed, and a correction of a previous result [C.‐S. Yih, J. Fluid Mech. 28, 493 (1967)] is made.

ISSN:0031-9171    

DOI:10.1063/1.1691941

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

An analytical solution to the problem of rarefied gas flow in a channel is obtained by the moment method. The expected minimum in volume flow rate is found; the flow rate exhibits an algebraic instead of a logarithmic singularity at low pressures. Present results are compared with the results from other theories and with measurements.

ISSN:0031-9171    

DOI:10.1063/1.1691942

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The Nocilla wall reflection model has been applied in the calculation of coefficients for aerodynamic lift and drag for simple shapes in free‐molecule flows. The desirability of a model more general than the Maxwellian re‐emission model is underscored through a brief discussion of recent experimental results. This discussion also serves as a guide for the selection of parameters essential to the present calculations. The Nocilla model is shown to constitute a formalism within which the free‐molecule kinetic theory can be carried forward with comparative ease. Normal and tangential momentum transfer are calculated on a mutually consistent basis and thermal accommodation is introduced in a manner which is consistent with the sources of such information relevant to highly directed flows.

ISSN:0031-9171    

DOI:10.1063/1.1691943

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The heat conduction and density distributions were experimentally determined for rarefied gases at rest contained between two unequally heated parallel plates. Both argon and nitrogen were used as test gases. Particular attention was focused on obtaining measurements in the transition regime where the ratio of plate spacing to mean free path was between 1 and 20. The gas density distribution was measured by observing the luminescence produced by a high‐energy electron beam traversed between the plates. The experimental results for argon were compared with the analytical results of Wang Chang and Uhlenbeck, Gross and Ziering, and Lees. In computing these results the thermal accommodation coefficient measured in the free‐molecule regime was used with the assumption that its value remained constant over the entire pressure range. The average agreement between the heat conduction data and the results of the four‐moment methods of Lees and Gross‐Ziering was about 2%, while the measured density profiles agreed with the results of these analyses within 3%. Both the heat conduction and density distribution data differ by ∼10‐20% from the results of Gross‐Ziering's eight‐moment method.

ISSN:0031-9171    

DOI:10.1063/1.1691944

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Previous theoretical investigation of sound propagation in rarefied gases is clarified and extended with emphasis on the role played by gas–surface interaction effects. The problem is formulated for the case of one‐dimensional motion generated by a piston undergoing small amplitude sinusoidal oscillation where the Knudsen number based on the distance from the piston is large. The resulting dispersive properties such as phase velocity and attenuation rate are in qualitative agreement with experimental data and previous theoretical predictions. However, the dependence of dispersion on the molecule–surface interaction is found to be quantitatively different from that suggested by earlier investigators.

ISSN:0031-9171    

DOI:10.1063/1.1691945

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The matrix elements of the linearized Boltzmann collision operator with respect to the Burnett functions are constructed for arbitrary power law potentials. The result of Mott‐Smith for elastic spheres appears as a special case.

ISSN:0031-9171    

DOI:10.1063/1.1691947

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The exact master equation of Prigogine and Re´sibois is derived for inhomogeneous as well as homogeneous systems. The asymptotic master equation is obtained from the following postulate: The singularities of the analytically continued Liouville resolvent nearest the real axis are isolated simple poles arising from “irreducible vacuum‐to‐vacuum” transitions. The asymptotic distribution function found in this way differs from the one obtained previously. If the asymptotic distribution function at time t1, fa(t1) is taken as a new initial value in the exact master equation, and the subsequent asymptotic solution is calculated for a time t2later, the result is fa(t1 + t2).

ISSN:0031-9171    

DOI:10.1063/1.1691948

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

A class of exact solutions of the full, viscous magnetohydrodynamic equations are generalized. This class of solutions has the property that the nonlinear terms in the governing equations are not zero identically but as a whole they cancel each other such that the remainder is linear and solvable. The governing equations are formulated using general orthogonal coordinates. Examples in Cartesian coordinates are illustrated. These exact solutions represent a wide variety of flows with probable astrophysical or engineering applications. In each case, the velocity field and the magnetic field are completely coupled.

ISSN:0031-9171    

DOI:10.1063/1.1691949

出版商:AIP    

年代:1968

数据来源: AIP