摘要:

The simplified mathematical model for two‐phase displacement in a Hele–Shaw cell, i.e., slow flow between closely spaced parallel plates, has been extended to include effects arising from a constant rate of rotation of the system. A linear stability analysis for an initially concentric circular drop reveals that it is unstable both to translation and, depending on the rotation rate, to a number of fingering modes. The nonlinear evolution with time of two of these modes is traced using a boundary‐integral numerical scheme. Ultimately, the liquid mass will break up into a number of drops. Apart from small distortion due to the Coriolis force, the patterns formed are essentially independent of both the liquid viscosity and the cell plate spacing or porous‐medium permeability. Potential application areas include certain aspects of coating flows, mold filling, and a class of liquid‐filled spinning projectiles with permeable packing.

ISSN:0899-8213    

DOI:10.1063/1.857543

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Two vertical, rotating flaps are used to generate a vortex pair beneath a free surface. Vortex pair formation, propagation, and interaction with a free surface are described. Numerical simulations for inviscid flow about a constant upwash sheet of vorticity beneath a free surface agree with experiment up to the time that turbulent mixing occurs during interaction with the free surface. The spacing between the vortex pairs then becomes larger than the calculated spacing. The experiments and lines of marked particles included in the simulations show fluid ingestion and transport toward the free surface.

ISSN:0899-8213    

DOI:10.1063/1.857482

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

A vortex model for a free shear layer with a wake component is proposed. The layer is represented by a curve which supports both a vortex sheet and a vortex‐dipole sheet. The vortex sheet yields a monotonic velocity profile that connects the outer flows on either side of the shear layer. The vortex‐dipole sheet captures the effect of oppositely signed vorticity that is present in the wake due to boundary layers upstream from the separation point. The equations governing a vortex‐dipole sheet are given and a temporal instability calculation for a free sinusoidal wake shows the development of a vortex street.

ISSN:0899-8213    

DOI:10.1063/1.857483

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The correspondence principle postulated for the description of hydrodynamic turbulence [Phys. Rev. Lett.57, 1722 (1986)] combined with the theory of thermal boundary layer [B. Castaingetal. (private communication)] is applied to high Rayleigh number convection in a Be´nard cell. Quantitative interpretation of recent experimental data [B. Castaingetal. (private communication)] is presented. The predicted intermittency exponent following from comparison of the theory with experiment is 0.175<&mgr;<0.275. A crucial experimental test of the renormalization group theory of turbulence is proposed.

ISSN:0899-8213    

DOI:10.1063/1.857484

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The flow outside a solid wedge that abruptly diverges at an angle of 18° was investigated experimentally. A turbulent boundary layer, which separated at the discontinuity and turned into a mixing layer downstream of it, reattached as a result of harmonic excitation at the apex of the wedge. Preliminary results indicate that this might be an effective way to delay separation of turbulent and laminar boundary layers.

ISSN:0899-8213    

DOI:10.1063/1.857555

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The onset of filamentation for compact vortex structures in two‐dimensional incompressible flows is elucidated. An estimate is presented for the filamentation time of an unstably perturbed Kirchhoff ellipse, obtained from a linear analysis of the geometry of the instantaneous corotating streamfunction.

ISSN:0899-8213    

DOI:10.1063/1.857485

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Space and time correlation functions in a randomly stirred turbulent fluid are evaluated to lowest order of the &egr; expansion in the renormalization group theory of turbulence. It is shown that wavenumber and frequency energy spectra differ substantially since random sweeping effects on the small eddies by large‐scale eddies do not contribute to the decorrelation in the RNG theory.

ISSN:0899-8213    

DOI:10.1063/1.857486

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Based on the recognition that the spatial probability density of velocity gradients and vorticity in a fully developed turbulence is nearly exponential, the scale‐similar dissipation cascade in a locally isotropic turbulence is reconsidered. With this, a new model of dissipation cascade that has a quality different from the other models known at present is constructed. Various aspects of the model are outlined and compared with the existing models and further experiments.

ISSN:0899-8213    

DOI:10.1063/1.857487

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Based on the observation of vortex splitting in the laminar wake of thin flat plates placed parallel to the flow, an investigation on the consequences of such events for the von Ka´rma´n vortex street in the wake of circular cylinders was carried out. It was found that a ‘‘design break line’’ of vortex axes can lead to the decoupling of a wake flow from the always present disturbances deriving from the ends. The decoupling gives rise to parallel vortex shedding of a slightly higher frequency, instead of the oblique or slanted vortex shedding at a lower frequency usually observed.

ISSN:0899-8213    

DOI:10.1063/1.857488

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

A model for Stokes flow through a channel with a stenosis is presented for both two‐dimensional motion and three‐dimensional flow with axial symmetry. Expressions are found for both the axial velocity and wall stress on the boundary.

ISSN:0899-8213    

DOI:10.1063/1.857489

出版商:AIP    

年代:1989

数据来源: AIP