The physical mechanisms for vortex breakdown which, it is proposed here, rely on the production of a negative azimuthal component vorticity, are elucidated with aid simple, steady, inviscid, axisymmetric equation motion. Most studies use as starting point an vorticity (Squire 1960), but departure in present study that explored directly and not through perturbations initial stream function. inviscid motion derived leads to criterion based generation some surfaces. Inviscid predictions tested...

A comparison between the experimental visualization and numerical simulations of occurrence vortex breakdown in laminar swirling flows produced by a rotating endwall is presented. The visualizations Escudier (1984) were first to detect presence multiple recirculation zones model presented here, consisting solution unsteady axisymmetric Navier-Stokes equations, faithfully reproduces these phenomena all other observed characteristics flow. Further, calculations elucidate onset oscillatory...

When the fluid inside a completely filled cylinder is set in motion by rotation of one endwall, steady and unsteady axisymmetric vortex breakdown possible. Nonlinear dynamical systems theory used to describe changing kinematics flow as speed rotating endwall increased. Two distinct modes oscillation have been found regime chaotic advection caused oscillations has investigated. The results this study are filling emptying processes bubbles observed visualization experiments.

Previous studies dealing with Floquet secondary stability analysis of the wakes circular and square cross-section cylinders have shown that there are two synchronous instability modes, long (mode A) short B) spanwise wavelengths. At intermediate wavelengths another mode arises, which reaches criticality at Reynolds numbers higher than modes A or B. Here we concentrate on these intermediate-wave number for cylinders. It is found in both cases possess complex-conjugate pair multipliers, can be...

A number of two-dimensional time-periodic flows, for example the Kármán street wake a symmetrical bluff body such as circular cylinder, possess spatio-temporal symmetry: combination evolution by half period in time and spatial reflection leaves flow invariant. Floquet analyses stability these flows to three-dimensional perturbations have past been based on Poincaré map, without attempting exploit symmetry. Here, analysis half-period-flip map provides comprehensive interpretation...

The bifurcation structure is presented for an axisymmetric swirling flow in a constricted pipe, using the pipe geometry of Beran and Culick [J. Fluid Mech. 242, 491 (1992)]. considered has been restricted to two-dimensional parameter space comprising Reynolds number Re relative swirl V0 incoming flow. diagram constructed by solving time-dependent Navier–Stokes equations. stability steady results Culick, obtained from code, confirmed. Further, solution branch also extended much larger values....

The flow in an enclosed rotating cylinder with a stationary lower end wall is investigated numerically. For fast rotation rates, the interior primarily azimuthal direction, angular momentum distribution very close to that corresponding solid-body for about inner-half radius. differential sets up large-scale circulation present boundary layers on top and sidewalls bottom wall, weak effusive component throughout bulk providing matching between layer flows bottom. has profile closely matches...

Hydrodynamics of surfactant monolayers are governed by surface tension, shear viscosity, dilatational and diffusivity. While the first two have been studied comprehensively with consistent results, viscosity is plagued anomalies, including apparent negative values. Here, full-field interfacial velocity measurements together Navier-Stokes equations reveal that a source these anomalies use equilibrium diffusivity for systems far from equilibrium. Specifically, diffisivity was found to be more...

Complex fluid interfaces are commonplace in natural and engineered systems a major topic the fields of rheology soft matter physics, providing boundary conditions for system’s hydrodynamics. The relationship between structure function dictates how constituents within complex fluids govern flow behavior via changing conformation response to local microenvironment minimize free energy. Both hydrodynamics, such as shear flow, presence air–liquid principal aspects fluid’s environment. study...

The flow driven by a rotating end wall in cylindrical container with aspect ratio H/R=2.5 is time dependent for Reynolds numbers Re=ΩR2/ν>2700. For up to 4000 three solution branches have been identified, and we examine on each one. At Re=3000, the axisymmetric periodic. Re=3500, quasiperiodic low-frequency modulation supports modulated wave azimuthal number k=5. Re=4000, periodic qualitatively different mode of oscillation that at Re=3500. It also wave, k=6. peak kinetic energy...

The flow in a stationary open cylinder driven by the constant rotation of bottom endwall is unstable to three-dimensional perturbations for sufficiently large rates. bifurcated state takes form rotating wave. Two distinct physical mechanisms responsible symmetry breaking are identified, which depend on whether fluid depth greater or less than radius. For deep systems, wave results from instability near-wall jet that forms as boundary layer turned into interior. In this case vanish at...

Rotating convection is analysed numerically in a cylinder of aspect ratio one, for Prandtl number about 7. Traditionally, the problem has been studied within Boussinesq approximation with density variation only incorporated gravitational buoyancy term and not centrifugal term. In that limit, governing equations admit trivial conduction solution. However, changes fundamental manner, driving large-scale circulation which cool denser fluid centrifuged radially outward warm less-dense inward, so...

Rotating convection in cylindrical containers is a canonical problem fluid dynamics, which variety of simplifying assumptions have been used order to allow for low-dimensional models or linear stability analysis from trivial basic states. An aspect the that has received only limited attention influence centrifugal force, because it makes difficult even impossible implement aforementioned approaches. In this study, mutual interplay between three forces problem, Coriolis, gravitational and...

In this paper, simulations are performed of the thermocapillary motion three-dimensional and axisymmetric drops in a confined apparatus. The refined level-set grid method is used to track interface resolve very small deformations. We compare our results theoretically predicted migration velocities experimentally measured microgravity experiments. motivation present work address four important questions surrounding migration. These as follows. (1) What impact initial conditions on both...

Abstract Plumes due to localized buoyancy sources are of wide interest owing their prevalence in many situations. This study investigates the transition from laminar turbulent dynamics. Several experiments have reported that this is sensitive external perturbations. As such, a well-controlled set-up has been chosen for our numerical study, consisting heat source at bottom an enclosed cylinder whose walls all maintained fixed uniform temperature, except source. At moderate Rayleigh numbers...

Direct numerical simulations of flows in cylinders subjected to both rapid rotation and axial precession are presented analysed the context a stability theory based on triadic resonance Kelvin modes. For case that was chosen provide finely tuned resonant instability with small nutation angle, good agreement previous experiments terms mode shapes dynamics, including long-time-scale regularization flow recurrent collapses. Cases not most unstable triad, but angle still small, also quite...

The flow in a completely filled rotating cylinder driven by the counter-rotation of top endwall is investigated both numerically and experimentally. basic state this system steady axisymmetric, but has rich structure radial axial directions. most striking feature, when sufficiently large, separation Ekman layer on endwall, producing free shear that separates regions with opposite senses azimuthal velocity. This unstable to disturbances supercritical symmetry-breaking Hopf bifurcation wave...

A numerical investigation of the multiple stable solutions found in confined swirling flows is presented. The consist fluid a completely filled cylinder driven by constant corotation two end walls. When reflectional symmetry at half-plane imposed, flow corresponds to that half height bottom wall, with top surface being flat and stress-free. Comparisons available experiments this case are made observed toroidal recirculation zones attached free described terms secondary motions induced...

The flow in a cylinder driven by the rotation of one endwall for height to radius ratios around three is examined. Previous experimental observations suggest that first mode instability precession central vortex core, whereas recent linear stability analysis general three-dimensional perturbations suggests Hopf bifurcation rotating wave at lower rates than those where was detected. Here, this apparent discrepancy resolved with aid fully nonlinear Navier–Stokes computations.