摘要:

Diffusion‐limited aggregation simulations of two‐fluid flow through porous media at infinite mobility ratio are extended to finite mobility ratio of driving to driven fluid. Curves for sweep efficiency at breakthrough are generated that come close to data obtained on two‐dimensional sand packs.

ISSN:0031-9171    

DOI:10.1063/1.865133

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The theory of nonlinear mode conversion is reviewed and applied to the ELMO Bumpy Torus (EBT) [Proceedingsofthe5thInternationalConferenceonPlasmaPhysicsandControlledNuclearFusionResearch1974(IAEA, Vienna, 1975), Vol. 2, p. 141] environment in the electron‐cyclotron, upper‐hybrid, lower‐hybrid, and ion‐cyclotron frequency ranges. A variety of parametric excitations in these frequency ranges is studied. Based on cascade saturation mechanisms, the parametric turbulence levels and corresponding anomalous absorption rates of the excited modes are evaluated. The relevance of nonlinear mode conversion for contemporary and future EBT experiments is discussed.

ISSN:0031-9171    

DOI:10.1063/1.865134

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Measurements have been made of the Stokes drag on a cylinder of length 2land diameter 2rfalling with its axis horizontal toward a horizontal plane boundary. The distance from the cylinder axis to the plane ish. Forl>2.48randh>3r, the results agree well with the slender body theory of de Mestre and Russel [J. Eng. Math.9, 81 (1975)]. Forl>19randh<0.5l, the theory of Jeffrey and Onishi [Q. J. Mech. Appl. Math.34, 129 (1981)] for a cylinder of infinite length is in good agreement with the experimental results; this theory also agrees well with the results for cylinders as short asl=0.89rin the regionh<2r. Measurements with tori indicate that the theory of Jeffrey and Onishi is not sensitive to curvature of the cylinder centerline in the horizontal plane. Forh>2land for all of the cylinders used (98r≥l≥0.89r) the data confirm the general boundary effect expression of Brenner [J. Fluid Mech.12, 35 (1962)]; and are in better agreement with Brenner’s expression than with the modified form proposed by Williams [J. Fluid Mech.24, 285 (1966)]. Forl>5r, the deceleration of the cylinder is observed to be constant when the cylinder velocity is between 0.4 and 0.15 of its value far from the wall, but the deceleration tends to zero as the velocity approaches zero.

ISSN:0031-9171    

DOI:10.1063/1.865135

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Fully developed flow of an incompressible Newtonian fluid driven by a pressure gradient through a square channel that rotates about an axis perpendicular to the channel roof is analyzed here with the aid of the penalty/Galerkin/finite element method. Coriolis force throws fast‐moving fluid in the channel core in the direction of the cross product of the mean fluid velocity with the channel’s angular velocity. Two vortex cells form when convective inertial force is weak. Asymptotic limits of rectilinear flow and geostrophic plug flow are approached when viscous force or Coriolis force dominates, respectively. A flow structure with an ageostrophic, virtually inviscid core is uncovered when Coriolis and convective inertial forces are both strong. This ageostrophic two‐vortex structure becomes unstable when the strength of convective inertial force increases past a critical value. The two‐vortex family of solutions metamorphoses into a family of four‐vortex solutions at an imperfect bifurcation composed of a pair of turning points.

ISSN:0031-9171    

DOI:10.1063/1.865136

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

This is a fundamental study of the phenomenon of natural convection in the region formed by a vertical warm wall rising above a cold horizontal wall, or in the region between a cold vertical wall extending downward from a warm horizontal surface. The study consists of scale analysis, numerical simulations, and an asymptotic solution of the low Rayleigh number limit. The scale analysis predicts the persistence of a single cell in the corner region, regardless of Rayleigh number. The cell migrates toward the corner as the Rayleigh number RaHincreases: the flow rate and the net heat transfer rate vary as Ra1/7H. The scale analysis is verified qualitatively and quantitatively by means of numerical experiments in the range RaH=103–107, Pr=0.7–7, H/L=1–4, where Pr is the Prandtl number and H/L is the height/length ratio of the corner region. Additional numerical simulations are presented for cases where one or both walls have uniform heat flux; in these cases, the heat transfer rate shows nearly the same behavior as when the corner walls are both isothermal. The asymptotic solution for the RaH→0 limit shows that the flow field is relatively insensitive to whether the wall temperature varies continuously or discontinuously through the corner point.

ISSN:0031-9171    

DOI:10.1063/1.865137

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A numerical‐perturbation scheme is used to determine the stability of incompressible flows past axisymmetric bodies with porous strips. Linear triple deck, closed‐form solutions are developed for the basic‐flow quantities, which account for upstream influence. These solutions are linear superpositions of the flow past the body without suction plus the perturbations caused by the suction strips. The flow past the suctionless body is calculated using the Transition Analysis Program System (TAPS). A perturbation scheme is used to determine the incrementaijin the complex wavenumber at a given locationsjbecause of the presence of a strip centered atsi. The end result is a set of influence coefficients that can be used to determine the growth rates and amplification factors for any suction levels without repeating the calculations. The influence coefficients are used to develop a simple linear optimization scheme to determine the number, spacing, and mass flow rate through the strips on an axisymmetric body.

ISSN:0031-9171    

DOI:10.1063/1.865138

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

An experimental study is described that deals with the nature of the entrainment zone of a linearly stratified fluid when the turbulence in the mixed layer is generated by an oscillating grid. Measurements include the interfacial‐layer thickness, frequency, and amplitude of the interfacial waves and the buoyancy flux at the entrainment interface. These measurements were compared with a theory proposed by Long [J. Fluid Mech.84, 43 (1978)], part of which (the mixed‐layer deepening law) has already been verified by Folseetal. [Phys. Fluids24, 396 (1981)]. After a certain depth of the mixed layer, the entrainment rate shows an abrupt increase, and this may possibly be caused by wall effects as shown in our previous investigations.

ISSN:0031-9171    

DOI:10.1063/1.865139

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The noise field generated by the motion of one, two, or several rectilinear vortices in an inviscid, irrotational mean flow past a step is considered for low Mach number. The streakline patterns of an impinging vortex are compared with flow visualization studies, and qualitative agreement between the present analytical results and the experiments is achieved. Both acoustic pressure and intensity are strong functions of the vortex motion near the step which, because of the complexity of the geometry, must be computed numerically. Results for the acoustic pressure and intensity are presented for a variety of incident vortex arrays.

ISSN:0031-9171    

DOI:10.1063/1.865140

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A theoretical and experimental study is reported of the lengthening and attenuation of triangular acoustic pulses of finite amplitude. The pulses studied in the laboratory are the leading portions of individualNwaves, which are produced in a conical‐driver shock tube. The facility has been used to produceNwaves with nondimensional pressure jumps across the leading front in the range 0.02–0.17. The length of the leading portion of the wave was measured in terms of its transit time at two different locations. Pulse lengthenings were measured in the weak shock wave range and were found to be in agreement with the well‐known theoretical predictions. On the other hand, our measurements of the pulse’s amplitude decay did not compare favorably with the same theory, mainly because of uncertainties associated with the flow field immediately behind the shock front. A new derivation of the theoretical predictions is also presented for lengthening and decay of a triangular pulse that is based on simple physical arguments.

ISSN:0031-9171    

DOI:10.1063/1.865411

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A small spherical, or cylindrical, pellet is imploded by an intensive, evenly distributed, short energy pulse. At the surface of the pellet the matter ionizes, its temperature and pressure rapidly rise, and the ablated plasma, by reaction, implodes the inner nucleus of the pellet. The involved structure of the energy absorbing zone is idealized and a sharp deflagration front is considered. With an almost square energy pulse, slightly dropping with time, the solution of the mass, momentum, and energy conservation equations of the compressed matter, is self‐similar. The differential equation of the nondimensional position of the deflagration front, its integral, and the magnitude and shape of the outside energy pulse are derived. The process of ablation is shown to depend solely on the nondimensional velocity of the gas just ahead of the deflagration front, minus the speed of sound, or the ratio of the gas densities across the deflagration front.

ISSN:0031-9171    

DOI:10.1063/1.865141

出版商:AIP    

年代:1985

数据来源: AIP