摘要:

SmecticsAare fluid, layered, materials which obey Darcy's law for flow normal to the layers, and an equation of the Navier‐Stokes type in the other two directions. The slow motions of various solid bodies inside a smectic are discussed, assuming that the layers are not distorted around the solid at rest. The flow pattern depends on a dimensionless parameter&kgr;L = SwhereLis the size of the object and&kgr;−1is a characteristic length of the smectic fluid. Only the limitS ≫ 1is considered. Depending on the shape of the object and on the direction of motion, either a velocity field confined to the smectic planes, but not very different from the Stokes flow in viscous fluids, or a “permeation layer” of thickness&dgr; ∼ &kgr;−1/2L1/2is found. In the latter case the drag is strongly enhanced. The idea of a permeation layer is also applied to a discussion of the undulation mode of a smectic sample between fixed plates, which has recently been studied by inelastic scattering of light.

ISSN:0031-9171    

DOI:10.1063/1.1694950

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The stability of an incompressible flat plate boundary layer with pressure gradient (Hartree pressure gradient parameter&bgr;= 1.0, 0.6, 0.4, 0.2, 0, −0.1, −0.14, and −0.1988) is computed from the linearized complete small disturbance equations. The analysis is nevertheless a quasiparallel treatment because although boundary layer growth is accounted for, the disturbance wave function is correct only in a strictly parallel flow. It is found that the nonparallel flow effect has a negligible influence on the critical Reynolds numberR&dgr;*−cfor0.4 ≤ &bgr; ≤ 1.0, but leads to a decrease inR&dgr;*−cin the range−0.1988 ≤ &bgr; ≤ 0.4. TheVterms lead to an increase inR&dgr;*−cin the range0.4 ≤ &bgr; ≤ 1.0, and to a decrease in the range−0.1988 ≤ &bgr; ≤ 0.4. The stream tube stretching term led to a decrease inR&dgr;*−cin the range0.4 ≤ &bgr; ≤ 1.0, and to an increase in the range0.4 ≥ &bgr; ≥ −0.1988. The effect of theVterms and the stream tube stretching term∂2U/∂x∂yappear to dominate all other boundary layer growth terms; nearR&dgr;*−cfor&bgr; = −0.1988however, the stream tube stretching term and∂2V/∂x2appear to be of the same order of magnitude.

ISSN:0031-9171    

DOI:10.1063/1.1694951

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An analysis has been performed of penetrative convective instabilities arising from the combined action of thermal and centrifugal buoyancy forces. The objective has been to examine the effect of various mean temperature and velocity profiles on the critical limit and convective penetration of the disturbances. The linearized perturbation equations have been solved employing an approximate technique. The close analogy between stream‐line curvature and thermal stratification effects has been demonstrated. It is found that for parallel layers of fluid along curved heated walls, a unique stability curve for neutral disturbances may be obtained if the quantity plotted along the abscissa isRa + &kgr;NG2where Ra is the Rayleigh number,NGis the Go¨rtler number, andkis a constant which expresses the relative importance of the mean temperature and velocity profiles.

ISSN:0031-9171    

DOI:10.1063/1.1694952

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The nonlinear development of a spatial growth wave in the shear layer of a circular jet is analyzed by an integral method based on energy considerations. The predicted development of the wave is in good agreement with the experimental data obtained previously except at the decaying portion of the flow. It also shows that the jet spreads more rapidly as the strength of the disturbance induced into the jet increases.

ISSN:0031-9171    

DOI:10.1063/1.1694953

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The flow induced by a pressure gradient along a pipe in a rapidly rotating system is examined for small but nonzero Rossby numbers. The regions of the flow field where inertial terms are important are identified and the flow determined for pipes of rectangular and circular cross section.

ISSN:0031-9171    

DOI:10.1063/1.1694954

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The phenomenological expressions of the slip velocity, slip temperature, the friction, and the heat transfer rate to the surface in the merged flow regime are determined by comparing the results of numerical integration of the Navier‐Stokes equations with experimental data over the sharp leading edge of a flat plate. The best agreement is obtained with the two‐stream slip models under the surface condition of total diffused reflection. The absolute error bound of the computed results is given as< 15%in the merged regime.

ISSN:0031-9171    

DOI:10.1063/1.1694955

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The flow of low concentrations of particles in a stagnation point fluid flow is studied. Particular attention is paid to the effect of the fluid pressure on the particle motion, and the boundary layer and its effects are considered. Conditions are found for the particles to be sedimented, that is, deposited on the wall. These conditions can be summarized as follows. If the drag is too small, the adverse pressure gradient will dominate the particle motion, and the particles may not approach the wall. If the drag is sufficiently large, the particles will all approach the wall, but may not reach the wall. However, if the inertia of the particles is sufficiently large, the particles will all be deposited on the wall.

ISSN:0031-9171    

DOI:10.1063/1.1694956

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The strengthening of a shock wave propagating through an isobaric region of increasing density was determined. A new experimental configuration consisting of a pressure driven shock tube mounted vertically with its test section partially immersed in a cryogenic bath was used in this study. The shock wave created by the diaphragm rupture propagated past a region of uniform low density through a strong local density gradient and finally into a high‐density zone. The Mach number of the shock emerging from the variable density region was measured and compared with results from approximate theoretical models. Mach numbers considerably higher than predicted were obtained and suggested the existence of shock strengthening processes not hypothesized in the previous theories but significant in this experimental configuration. Preliminary computations showed that multiple interactions between waves generated within the density gradient and flow nonuniformities due to the shock formation mechanism were of sufficient magnitude to explain the observed Mach numbers. This study contributes to the understanding of shock tube operation in the presence of a density gradient and provides a tool useful for experimentation in a cryogenic environment.

ISSN:0031-9171    

DOI:10.1063/1.1694957

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Conditions are established for determining whether the downstream state of a switch‐on hydromagnetic shock wave will be subsonic, sonic, or supersonic, thus giving an explicit criterion for the existence of a gasdynamic subshock within the overall structure. The analysis is made for the general case of an ionizing shock wave with nonzero electric field. The results include the well‐known magnetohydrodynamic case in the limit of zero‐electric field. Post‐shock temperatures are investigated, and it is found that it may be possible for an ionizing switch‐on shock to exist with a nonzero electric field without involving a gas‐dynamic subshock. In this case, the structure consists of an initial photoionization layer followed by magnetohydrodynamic compression giving a high‐temperature post‐shock region, the radiation from which drives the upstream photoionization.

ISSN:0031-9171    

DOI:10.1063/1.1694958

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An unsteady analysis is made of the nontorsionally generated hydromagnetic flow in a semiinfinite expanse of an electrically conducting rotating viscous fluid bounded by an infinite nonconducting porous plate with uniform suction or blowing in the presence of a transverse uniform magnetic field. The structure of the steady and the unsteady velocity distributions and the associated hydromagnetic multiple boundary layers are investigated including the case of blowing and resonant oscillations. Both the steady and the unsteady velocity fields describe the general features of the hydromagnetic boundary layer flows in the rotating fluid including the effects of uniform suction or blowing for all frequencies of oscillations of the plate. Unlike the hydrodynamic situation for the case of blowing and resonance, the hydromagnetic steady‐state solution satisfies the boundary condition at infinity and the associated boundary layers are confined to the plate. The inherent difficulty involved in the purely hydrodynamic problem associated with the case of blowing and the resonant frequency has been resolved in this paper by the addition of the magnetic field.

ISSN:0031-9171    

DOI:10.1063/1.1694959

出版商:AIP    

年代:1974

数据来源: AIP