Oscillation Of Cylinder Research Articles

Effect of Rotation on Steady Viscous Flow between Two Cylinders

In this paper steady viscous flow between two infinitely long circular cylinders produced by small-amplitude transverse vibrations of the inner cylinder about the axis of the outer cylinder and torsional oscillation of the outer cylinder about its axis is studied. The Vishik–Lyusternik method is employed to construct an asymptotic expansion of the solution of the Navier–Stokes equations in the limit of high-frequency vibrations for Reynolds numbers of order of unity. The effect of the Stokes drift of fluid particles is also studied. It is shown that it is nonzero not only within the boundary layers but also in higher order terms of the expansion of the averaged outer flow.

Effect of wall oscillation on dispersion in axi‐symmetric flows between two coaxial cylinders

AbstractLongitudinal dispersion of solute released in an unsteady flow between two coaxial cylinders is studied by employing the method of moments. The flow unsteadiness is caused by the oscillation of the outer cylinder in its own plane around the inner. A finite difference implicit scheme is adopted to solve the Aris integral moment equations arising from the unsteady convective‐diffusion equation for all time period. The behaviour of dispersion coefficient due to periodic flow with the variation of radius ratio, absorption parameter and frequency parameter has been examined. Assuming that the distribution of concentration is initially uniform over the cross‐section of the annulus, it is shown that, like the case of oscillatory flow caused by periodic pressure gradient, dispersion coefficient can be diminished by increasing absorption at the boundary. The radius ratio of the annular tube is found to have variable effect on the dispersion coefficient depending on the position (inner or outer) of the oscillatory tube. The axial distributions of mean concentration are approximated using Hermite polynomial representation from the first four central moments for a range of different radius ratios, absorption parameters, and frequencies of the wall oscillation. It has been found that the peak of the concentration distribution increases with increase in frequency parameter and radius ratio but opposite trend follows for the absorption parameter.

Study on In-Flow Oscillation of Couples of Cylinders by Cross-Flow

The importance of the in-flow oscillation of a single cylinder in cross-flow has been in the spotlight since an accident in a FBR-type reactor. However, in-flow oscillations can also be observed in heat exchanger tube arrays. Previous reports show some interesting phenomena on the oscillation of cylinder arrays. In this paper, detailed observation on the effect of the pitch ratio for pairs of cylinders, in parallel and in tandem, is highlighted in the range of low flow velocities, where each cylinder can move only in a given direction. The motion of the cylinders is measured by attached strain gages and by a high-speed digital video camera. As a result, it is found that the response of cylinders is greatly affected by their pitch ratio due to the separated vortex, and that the symmetric vortex is restricted when the motion of cylinder is restricted.

J091011 円柱のカルマン渦励振および縦渦励振における同期現象と揚力特性([J09101]流体関連の騒音と振動(1))

J091011 円柱のカルマン渦励振および縦渦励振における同期現象と揚力特性([J09101]流体関連の騒音と振動(1))

Numerical Experiments of Forced Cylinder Oscillations at an Angle to Oncoming Flow

A computational study of laminar, incompressible flow past a circular cylinder forced to oscillate in the longitudinally, transversely and at an angle to the uniform freestream is performed using the dynamic mesh method. The numerical simulations are conducted at a fixed Reynolds number of 80 and 300 with amplitude ratios from 0.05 to 0.7 and excitation frequency ratios of 0.05 to 3.0. Excellent agreement to previous experimental and numerical investigations is achieved in the prediction of the lock-on range, force amplifications and vortex-shedding modes. Analysis of the wake response of flow past a cylinder oscillating at an angle to the free stream using phaseplane diagrams and the transverse force coefficients revealed two lock-on regions. The extents of these lock-on regions, the variation of the forces, and the near-wake vortex shedding modes are discussed and presented.

Two phenomena: Honji instability, and ringing of offshore structures

Honji instability and ringing of offshore structrures are two different phenomena. Honji instability occurs at a circular cylinder in transverse periodic finite motion in a water tank. It is superposed on the streaming flow induced by the cylinder's boundary layer. Its oscillation period is half of the period of the cylinder oscillation. Finite volume calculations of the filtered Navier-Stokes equations visualize the three-dimensional instability, where fluid particles transported by the circumferencial roll pairs exhibit a periodic mushroom-like pattern. Force is the same with and without the Honji instability. The large eddy simulation calculations for high Reynolds number support a drag coefficient in accordance with the Stokes-Wang solution below separation and conform with experimental measurements of the damping force on a harmonically oscillating cylinder. Ringing of offshore structures are vibrations which appear at natural frequencies and concern fatigue. It is generated by a higher harmonic force oscillating with frequency being 3–4 times the fundamental wave frequency. Together with a strong inertia load in phase with the incoming wave's acceleration, a secondary load cycle appears in strong seas when the wave crest leaves the structure; this occurs about 1/4 wave period after the main force peak, it starts when the wave crest is about one cylinder radius behind the cylinder, lasts for about 15–20 percent of the wave period and has a magnitude up to 11 % of the peak-to-peak total force. It is a gravity effect and appears in strong irregular seas when kA > 0.18 and um/gD>0.4 (k wavenumber, A amplitude, um maximal wave induced velocity, g acceleration of gravity, D cylinder diameter).

Numerical simulation of an elementary Vortex-Induced-Vibration problem by using fully-coupled fluid solid system computation

Numerical simulation of Vortex-Induced-Vibrations (VIV) of a rigid circular elastically-mounted cylinder submitted to a fluid cross-flow has been extensively studied over the past decades, both experimentally and numerically, because of its theoretical and practical interest for understanding Flow-Induced-Vibrations (FIV) problems. In this context, the present article aims to expose a numerical study based on fully-coupled fluid-solid computations compared to previously published work [34], [36]. The computational procedure relies on a partitioned method ensuring the coupling between fluid and structure solvers. The fluid solver involves a moving mesh formulation for simulation of the fluid structure interface motion. Energy exchanges between fluid and solid models are ensured through convenient numerical schemes. The present study is devoted to a low Reynolds number configuration. Cylinder motion magnitude, hydrodynamic forces, oscillation frequency and fluid vortex shedding modes are investigated and the “lock-in” phenomenon is reproduced numerically. These numerical results are proposed for code validation purposes before investigating larger industrial applications such as configurations involving tube arrays under cross-flows [4].

Streamwise oscillations of a cylinder beneath a free surface: Free surface effects on vortex formation modes

A computational study of a viscous incompressible two-fluid model with an oscillating cylinder is investigated at a Reynolds number of 200 and at a dimensionless displacement amplitude of A=0.13 and for the dimensionless forcing cylinder oscillation frequency-to-natural vortex shedding frequency ratios, f/f0=1.5,2.5,3.5. Specifically, two-dimensional flow past a circular cylinder subject to forced in-line oscillations beneath a free surface is considered. The method is based on a finite volume discretization of the two-dimensional continuity and unsteady Navier–Stokes equations (when a solid body is present) on a fixed Cartesian grid. Two-fluid model based on improved volume-of-fluid method is used to discretize the free surface interface. The study focuses on the laminar asymmetric flow structure in the near wake region and lock-on phenomena at a Froude number of 0.2 and for the dimensionless cylinder submergence depths, h=0.25, 0.5 and 0.75. The equivorticity patterns and pressure distribution contours are used for the numerical flow visualization. The code validations in special cases show good comparisons with previous numerical results.

Erratum: “Oscillation of cylinders of rectangular cross section immersed in fluid” [Phys. Fluids 22, 052001 (2010)

Erratum: “Oscillation of cylinders of rectangular cross section immersed in fluid” [Phys. Fluids 22, 052001 (2010)

A TIME-INDEPENDENT FINITE DIFFERENCE ANALYSIS OF VISCOUS FLOW ACROSS A TRANSLATING CIRCULAR CYLINDER

A time-independent finite difference scheme is developed and applied to analyze the viscous flow past a translating circular cylinder. In this scheme, the instantaneous moving cylinder face is mapped to a fixed boundary and the computational domain is, therefore, time independent. Large Reynolds number and high oscillating frequency of moving cylinder are used in the analysis. The finite difference approximation and algorithm were validated by the reported numerical simulation and flow visualization. The vorticity and streamline patterns developments were described and discussed. The surface vorticity distribution and position of separation point versus phases of oscillating stages were discussed. The flow behaviors of various amplitudes of exciting velocity and frequencies of moving cylinder are simulated and compared. The in-line forces on cylinder during cylinder oscillation were calculated and are in good agreement with those predicted by Morison’s equation. The developed scheme can be extended to analyze the viscous flow passing an arbitrary moving cylinder.

Finite element analysis of natural heat transfer from an isothermal array of cylinders in presence of vertical oscillations

A numerical simulation is performed to study the effects of vertical vibrations on natural convection heat transfer in an array of isothermal circular cylinders. Governing equations consist of continuity, momentum and energy equations were solved numerically by finite element method and Arbitrary Lagrangian–Eulerian kinematics description. The results showed that vertical oscillations of cylinders do not necessarily results in increment of average Nusselt number of each cylinder.

Generation, propagation, and breaking of an internal wave beam

We report upon an experimental study of internal gravity waves generated by the large-amplitude vertical oscillations of a circular cylinder in uniformly stratified fluid. Quantitative measurements are performed using a modified synthetic schlieren technique for strongly stratified solutions of NaCl or NaI. The oscillatory forcing leads to the development of turbulence in the region bounding the cylinder. This turbulence is found to be the primary source of the observed quasimonochromatic wave beams, whose characteristics at early times differ from theoretical predictions and experimental investigations of waves generated by small-amplitude cylinder oscillations. In particular, their wavelength is set by the Ozmidov scale rather than the size of the cylinder. The wave frequency is set by the buoyancy frequency N if the cylinder frequency is larger or much less than N. Otherwise it is set by the cylinder oscillation frequency. Over long times the finite-amplitude waves that have propagated away from their source are observed to break down and the process is examined quantitatively through conductivity probe measurements and qualitatively through unprocessed synthetic schlieren images. From an analysis of the location of wave breakdown we determine that the likely mechanism for breakdown is through parametric subharmonic instability. This conclusion is supported by fully nonlinear numerical simulations of the evolution of a temporally, although not spatially, monochromatic internal wave beam.

Convective heat transfer from a rotating cylinder with inline oscillation

In this study convective heat transfer from a rotating cylinder with inline oscillation is studied using a finite element method based on the Characteristic Based Split method (CBS) to solve governing equations consisting of continuity, full Navier–Stokes, and energy equations. Employing the Arbitrary Lagrangian-Eulerian (ALE) formulation, the dynamic unstructured triangular grid used here is accompanied by lineal and torsional spring analogy to consider large boundary movements. Simulations are conducted to study convective heat transfer past a rotating cylinder with inline oscillation at Reynolds numbers of 100, 200 and 300. Different rotational speeds of the cylinder in the range of 0–2.5 are considered at various oscillating amplitudes and frequencies with three different Prandtl numbers of 0.7, 6 and 20. Effects of oscillation and rotation of cylinder on the temperature and flow field, vortex lock-on, mean Nusselt number, and the pattern of vortex shedding are investigated in detail at constant temperature boundary condition on the cylinder surface. It is found that similar to the fixed cylinder, beyond a critical rotating speed, the vortex shedding is strongly suppressed. Furthermore, as the rotational speed of the cylinder increases, both the Nusselt number and the drag coefficient decrease rapidly. In the vortex lock-on region, the Nusselt number increases rapidly.

LAMINAR FLOW PAST AN OSCILLATING CIRCULAR CYLINDER IN CROSS FLOW

The present study numerically investigates the twodimensional laminar flow past a circular cylinder forced to oscillate transverse to the free-stream. The numerical simulations are performed at a various range of cylinder oscillation frequency ranged between 0.8 and 1.2 of the natural vortex shedding frequency, and the oscillation amplitude extended up to 50% of the cylinder diameter at one Reynolds number of 185 showing the typical two-dimensional vortex shedding. The immersed boundary method is used to handle the oscillating cylinder in a rectangular grid system using the finite volume method. The primary vortex shedding frequency has the same value with the exciting frequency. When the exciting frequency exceeds the natural vortex shedding frequency, the secondary vortex shedding frequency appeared with the value less than the natural shedding frequency. The time sequence of the wake structures near the cylinder at the extreme upper position reveals that a single vortex or a pair of vortices appears according to the time. A pair of vortices is composed of two saddle points and two centers of vortices, showing the occurrence of vortex switching phenomenon. The quantitative information about the flow variables such as the distribution of wall vorticity on the cylinder surface, drag and lift coefficients is highlighted.

An adaptive version of ghost-cell immersed boundary method for incompressible flows with complex stationary and moving boundaries

An adaptive version of immersed boundary method for simulating flows with complex stationary and moving boundaries is presented. The method employs a ghost-cell methodology which allows for a sharp representation of the immersed boundary. To simplify the implementation of the methodology, a volume-of-fluid method is introduced to identify the immersed boundary. In addition, the domain is spatially discretized using a tree-based discretization which is relatively simple to implement a fully flexible adaptive refinement strategy. Finally, the methodology is validated by comparing it with numerical and experimental results on three cases: (1) the flow passing a circular cylinder at Re=40 and Re=100, (2) a periodic oscillation of a circular cylinder in fluid at rest and (3) the self-propelled fish-like swimming at Re=6400.

Oscillation of cylinders of rectangular cross section immersed in fluid

The ability to calculate flows generated by oscillating cylinders immersed in fluid is a cornerstone in micro- and nanodevice development. In this article, we present a detailed theoretical analysis of the hydrodynamic load experienced by an oscillating rigid cylinder, of arbitrary rectangular cross section, that is immersed in an unbounded viscous fluid. We also consider the formal limit of inviscid flow for which exact analytical and asymptotic solutions are derived. Due to its practical importance in application to the atomic force microscope and nanoelectromechanical systems, we conduct a detailed assessment of the dependence of this load on the cylinder thickness-to-width ratio. We also assess the validity and accuracy of the widely used infinitely-thin blade approximation. For thin rectangular cylinders of finite thickness, this approximation is found to be excellent for out-of-plane motion, whereas for in-plane oscillations it can exhibit significant error. A database of accurate numerical results for the hydrodynamic load as a function of the thickness-to-width ratio and normalized frequency is also presented, which is expected to be of value in practical application and numerical benchmarking.

Combined action of transverse oscillations and uniform cross-flow on vortex formation and pattern of a circular cylinder

This paper attempts to study the roles of lateral cylinder oscillations and a uniform cross-flow in the vortex formation and wake modes of an oscillating circular cylinder. A circular cylinder is given lateral oscillations of varying amplitudes (between 0.28 and 1.42 cylinder-diameters) in a slow uniform flow stream (Reynolds number=284) to produce the 2S, 2P and P+S wake modes. Detailed flow information is obtained with time-resolved particle-image velocimetry and the phase-locked averaging techniques. In the 2S and 2P mode, the flow speeds relative to the cylinder movement are less than the uniform flow velocity and it is found that initial formation of a vortex is caused by shear-layer separation of the uniform flow on the cylinder. Subsequent development of the shear-layer vortices is affected by the lateral cylinder movement. At small cylinder oscillation amplitudes, vortices are shed in synchronization with the cylinder movement, resulting in the 2S mode. The 2P mode occurs at larger cylinder oscillation amplitudes at which each shear-layer vortex is found to undergo intense stretching and eventual bifurcation into two separate vortices. The P+S mode occurs when the cylinder moving speeds are, for most of the time, higher than the speed of the uniform flow. These situations are found at fast and large-amplitude cylinder oscillations in which the flow relative to the cylinder movement takes over the uniform flow in governing the initial vortex formation. The formation stages of vortices from the cylinder are found to bear close resemblance to those of a vortex street pattern of a cylinder oscillating in an otherwise quiescent fluid at Keulegan–Carpenter numbers around 16. Vortices in the inclined vortex street pattern so formed are then convected downstream by the uniform flow as the vortex pairs in the 2P mode.

Numerical simulation of cylinder oscillation by using a direct forcing technique

Fluid–structure interaction (FSI) is an important safety issue of nuclear components such as reactor vessel internals, heat exchangers, steam generators and piping, etc. For instance, when continuous repetitive flow is rapidly exerted on cylinders, resulting oscillation induces high vibration that may lead to fretting wear on the contact surface of cylinder. In the present research, to assess vibration characteristics of cylinders in fluidic channels, a modified immersed finite element method (IFEM) is developed by using a direct forcing technique coupled with cylinder oscillation. Then, this method is tested for an elastically mounted cylinder in still fluid or subjected to uniform inlet fluid flow and further a simple tube bundle to examine effects of vibration-related parameters.

Vortex formation processes from an oscillating circular cylinder at high Keulegan–Carpenter numbers

Development of vortex patterns around a circular cylinder oscillating in quiescent water is investigated using time-resolved particle image velocimetry. Experiments are performed at Keulegan–Carpenter (KC) numbers between 8 and 36 with Reynolds number kept constant at 2400. Similar to previous studies, three modes of vortex patterns are identified and denoted as modes I, II, and III. The development of vortices in each mode at successive phases of cylinder oscillation is studied in details. The classification of modes is based on the development mechanism of shear layers around the cylinder, the number of vortices shed in each half cycle, and the characteristics of the vortex street. Modes I, II, and III are characterized by one, two, and three (or more) vortices generated, respectively, in each half cycle. The appropriate vortex formation length is applied to explain the dependence of number of vortices formed in each cylinder cycle on KC. Vortex shedding in mode I occurs only on one side of the line of cylinder motion. This mode, which occurs at KC between 8 and 16, is observed to have two submodes with different orientations of the vortex street to the line of cylinder motion. Mode II occurs at KC between 16 and 24. The vortex street extends to both sides of the line of cylinder motion and lies at about 45° to it. At KC>24, vortices are shed behind the moving cylinder similar to the case of a towed cylinder. The limited-length vortex street in this mode III pattern lies along the line of cylinder motion. Each vortex pattern is associated with a typical secondary flow stream, which affects distinct evolution stages of vortices around the cylinder and hence the unique vortex pattern. The development of vortices is found to involve complex vortex interaction involving migration, stretching, and splitting.

114 角柱のギャロッピングに対する後流物体の影響(GS7-3 流体工学)

114 角柱のギャロッピングに対する後流物体の影響(GS7-3 流体工学)