摘要:

A simple classical model is used to investigate the roton‐quantized vortex line interaction, and the behavior of the roton in the vortex field is studied in detail. A process is found which results in a sizeable, long‐range transfer of momentum between a roton and the core. The scattering is unsymmetric about the forward direction. From this model it is possible to derive the Hall‐Vinen mutual friction terms that appear in the phenomenological equations of motion for liquid He II. Calculated values of theBandB′coefficients are in agreement with experiments forT<1.6°K. The parameters in the theory are chosen from considerations independent of the present problem.

ISSN:0031-9171    

DOI:10.1063/1.1693603

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The force exerted by an incompressible inviscid fluid upon a stationary rigid sphere is calculated for an arbitrary potential flow incident upon the sphere. The result is applied to a sphere in the steady flow produced by a line vortex.

ISSN:0031-9171    

DOI:10.1063/1.1693604

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A simplified theoretical model is used for the successful description of measured impulsively started spin‐up and impulsively stopped spin‐down times in a finite cylindrical geometry at a Reynolds numberRof 1002. The essential physical idea used in the analysis is very rapid establishment of steady‐state boundary‐layer flows in times that are short compared with spin‐up and spin‐down times in the interior (core) of the liquid (water).

ISSN:0031-9171    

DOI:10.1063/1.1693605

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Two intermittency signals on each side of a two‐dimensional jet were correlated to determine the manner in which boundaries move relative to one another. With some minor reservations it is concluded that each boundary moves independently.

ISSN:0031-9171    

DOI:10.1063/1.1693606

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

An analysis of internal flows with surface mass transfer is performed in which account is taken of velocity slip at the surface of the porous bounding wall. The solutions for channel and tube flows reveal a variety of interesting effects of velocity slip, which depend upon whether fluid is injected or withdrawn at the bounding wall and upon the sign of the streamwise pressure gradient. For example, relative to the situation in which there is no slip, the streamwise pressure gradient may either increase or decrease in the presence of slip and may even undergo a change of sign.

ISSN:0031-9171    

DOI:10.1063/1.1693607

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The linear stability problem for a fluid in a classical Be´nard geometry, when the temperature gradient has both a steady and a time‐periodic component, is considered. The modulating effect of the oscillatory gradient on the stability characteristics of the basic configuration is examined. It is found that, in general, there is enhancement of the critical value of a suitably defined Rayleigh number.

ISSN:0031-9171    

DOI:10.1063/1.1693608

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The stability of turbulent plane flow profiles subject to infinitesimal disturbances is studied. Neutral stability curves are found for a number of velocity profiles varying from parabolic Poiseuille flow to a profile approaching that of turbulent flow. As the profile varies from the parabolic case, the flow is always stabilized.

ISSN:0031-9171    

DOI:10.1063/1.1693609

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The evolution of moments of the concentration of each of the species in a two‐species, very rapid, isothermal, irreversible, second‐order, chemical reaction in a homogeneous turbulence is described in terms of assumed initial distributions of the concentration fields. The fields decay in two stages. In the stage dominated by chemical kinetics, exact stochastic solutions are derived for a class of initial distributions. These solutions exhibit asymptotic concentration fields having an extremely high relative intensity and skewness associated with the spatial segregation of the species. In the second or diffusion controlled stage exact solutions are obtained in terms of the turbulent mixing of a nonreacting species when the molecular diffusivities of the species are equal. An approximate solution is proposed when they are unequal. In both cases the time scale of decay in the second stage is entirely characterized by turbulent mixing parameters. It is shown that in final period turbulence the reactants decay with an effective diffusivity of the same order as the smaller of the two diffusivities.

ISSN:0031-9171    

DOI:10.1063/1.1693610

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The first‐order transient contribution to the strong‐interaction induced pressure has been obtained for a suddenly accelerated semi‐infinite flat plate moving at hypersonic speed and zero angle of attack. The unsteady compressible laminar two‐dimensional boundary‐layer equations are employed in self‐similar form incorporating the Dorodnitsyn‐Howarth and similarity transformations. The linear viscosity‐temperature law is used in the analysis. The solution to the coupled set of governing equations has been found numerically for Prandtl number unity and for zero and nonzero wall heat transfer. The obtained solutions are utilized to compute the unsteady displacement thickness and subsequently the induced pressure. Numerical results have also been obtained for the transient distribution of the wall shear and wall heat transfer for one percent change in the plate velocity. There is a discontinuity in the solutions which corresponds to Stewartson's singularity at&tgr; = 0.

ISSN:0031-9171    

DOI:10.1063/1.1693611

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The problem of evaporation from an interphase and the problem of heat conduction in a gas are studied on the basis of the linearized single‐relaxation model equation. Both problems lead to the same set of integral equations. Exact values are obtained for the microscopic temperature and density jumps. It is found that the macroscopic temperature and density jumps of the evaporation problem can be expressed in terms of the macroscopic jumps of the heat conduction problem and vice versa. A proof for the existence and uniqueness of the solutions is also given.

ISSN:0031-9171    

DOI:10.1063/1.1693612

出版商:AIP    

年代:1971

数据来源: AIP