摘要:

The relations between Lagrangian and Eulerian probabilities are obtained for the case of variable density of fluid. The general stochastic model for trajectories in nonhomogeneous turbulence is considered, and probability for Lagrangian forcing is expressed in terms of Eulerian distribution. The criterion of the influence of boundaries on the asymptotic behavior of trajectories is presented.

ISSN:0031-9171    

DOI:10.1063/1.865778

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The presence of wave propagation on vortex trails has been pointed out by Tritton [J. Fluid Mech.6, 547 (1959)] who measured their speeds in the wake of a cylinder at moderate Reynolds numbers. It is shown here that the von Karman model of the vortex trail leads to such disturbance waves and, moreover, that they can be of growing amplitude. The theoretical values of the wave speeds are found to lie within the experimental error bounds.

ISSN:0031-9171    

DOI:10.1063/1.865779

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The existence of coherent structures in mixing layers is now well‐known but some aspects of their dynamics are not clarified. In particular, the influence of the eigenfrequency of the experimental apparatus on the layer development is generally not studied. The present experimental evidence indicates that the frequency response of an apparently unexcited plane mixing layer is, in fact, a characteristic of the setup.

ISSN:0031-9171    

DOI:10.1063/1.865780

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A simple composite time scale model for third‐order scalar‐velocity correlations under negligible effect of buoyancy is proposed as &tgr;3∝&tgr;u(1+b&tgr;&thgr;/&tgr;u), where &tgr;uis a dynamic time scale (≡q¯2/&egr;) and &tgr;&thgr;is a scalar time scale (≡&thgr;¯2/&egr;&thgr;). The constantbrepresents relative influence of &tgr;&thgr;over &tgr;uon the spatial transport of second‐order moments. Its value depends on the power of the scalar fluctuations &thgr; in the third‐order moments. The model predictions are in excellent agreement with experimental data in a turbulent scalar diffusion field behind a line heat source in a uniform shear flow.

ISSN:0031-9171    

DOI:10.1063/1.865781

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A magnetic probe array is utilized to perform current centroid measurements of a 4 kA, 700 kV, 100 nsec electron beam propagating in the ion focused regime. Results with several filling gases all show transverse oscillation, which may be indicative of hose‐type motions of the beam.

ISSN:0031-9171    

DOI:10.1063/1.865782

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

An experimental study of the drag on hollow cylinders and conglomerates falling in a viscous fluid under Stokes flow conditions is described. The experiments were carried out in a tank of square cross section using silicone oil as the Newtonian fluid. Settling velocities of the free falling objects were measured and corrected to conditions of zero Reynolds number flow in an unbounded fluid. The results reveal that all objects tested have Stokes settling velocities smaller than that of a sphere of equal mass and volume. Measurements are reported in terms of the settling speed ratio defined as the ratio of the Stokes settling speed to that of a sphere of equal mass and volume. For the hollow cylinders two parameters are varied: the aspect ratio (length to outside diameter) and the radius ratio (inner to outer radius). Measurements show that the settling speed ratio decreases markedly as the hollowness of the cylinder increases. Each fixed radius ratio data set exhibits a maximum settling speed ratio near an aspect ratio of 1.65. For conglomerates composed ofnspheres two trends appear: one for planar configurations and the other for globular clusters. Experimental data for two spheres and three spheres in point contact are in good agreement with recent theoretical results.

ISSN:0031-9171    

DOI:10.1063/1.865732

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The bulk‐averaged equations of motion, which describe the buoyancy driven flow in particle settlers having inclined walls, are solved over a wide range of the relevant parameter space. The solution assumes that the flow is laminar, that the particle Reynolds number is small, that the suspension is monodisperse, and that the settling occurs in a parallel plate vessel whose length to width ratio is not too large. It is shown that, in the asymptotic limit, &Lgr;→∞, where &Lgr; is the ratio of a sedimentation Grashof number to a sedimentation Reynolds number,R, inertial effects in the flow areO(&xgr;1/6), where &xgr; is given explicitly in terms ofR, &Lgr;, the inclination angle, &thgr;, and the dimensionless distance from the vessel bottom. Using regular and singular perturbation techniques, the asymptotic form of the equations for &Lgr;≫1 are then solved over the entire range of &xgr; and the solutions are shown to reduce to those given by Acrivos and Herbolzheimer [J. Fluid Mech.92, 435 (1979)] and by Schneider [J. Fluid Mech.120, 323 (1982)] in the limits &xgr;→0 and &xgr;→∞, respectively. Since typically in practice &Lgr;∼O(106–109), the present solutions give expressions for the velocity profiles and the thickness of the clear‐fluid slit that forms underneath the downward facing vessel wall, which are valid for a wide class of systems of practical interest.

ISSN:0031-9171    

DOI:10.1063/1.865733

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In this study a series of numerical simulations is reported that aims to document the phenomenon of buoyancy‐driven flow instability in a fluid layer extending over a porous substrate. The numerical simulations focus primarily on the parametric domain in which the flow in the system is well established, i.e., the value of the Rayleigh number is larger than critical. A general flow model is used to describe the flow inside the porous bed. This flow model accounts for friction caused by macroscopic shear [Brinkman extension of the Darcy model; Appl. Sci. Res. Sect. A1, 27 (1947)], as well as for the phenomenon of flow inertia [Forchheimer’s extension of the Darcy model; Dtsch. Ingenieure45, 1782 (1901)]. Several important characteristics of the flow and temperature fields inside the composite layer (porous/fluid) are reported and the dependence of these characteristics on the problem dimensionless groups is documented.

ISSN:0031-9171    

DOI:10.1063/1.865734

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Free surface flows of a liquid poured from a container are calculated numerically for various configurations of the lip. The flow is assumed to be steady, two dimensional, and irrotational; the liquid is treated as inviscid and incompressible; and gravity is taken into account. It is shown that there are jetlike flows with two free surfaces, and other flows with one free surface which follow along the underside of the lip or spout. The latter flows occur in the well‐known ‘‘teapot effect,’’ which was treated previously without including gravity. Some of the results are applicable also to flows over weirs and spillways.

ISSN:0031-9171    

DOI:10.1063/1.865735

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The problem of steady two‐dimensional flow, under the action of gravity, of an incompressible inviscid fluid sheet past a sluice gate is reexamined with particular reference to the theoretical prediction of the contraction ratio, i.e., the ratio of the far downstream height to the sluice opening. The problem is formulated here by a direct approach with the use of the theory of a directed fluid sheet, which includes appropriate jump conditions arising in a natural way within the scope of the basic theory. The determination of the contraction ratio is effected by a novel procedure in the utilization of the jump conditions at the gate. Detailed numerical calculations are made for two different sluice openings and these provide very good agreement with the experimental results of Benjamin [J. Fluid Mech.1, 227 (1956)].

ISSN:0031-9171    

DOI:10.1063/1.865736

出版商:AIP    

年代:1986

数据来源: AIP