Vortex Forces on an Oscillating Cylinder

2002 ◽  
Author(s):  
J. Carberry ◽  
J. Sheridan ◽  
D. Rockwell
Keyword(s):  
Vortex Shedding ◽  
Lift Force ◽  
Free Stream ◽  
Discontinuous Change ◽  
Near Wake ◽  
Oscillating Cylinder ◽  
Sinusoidal Oscillations ◽  
Lift And Drag ◽  
Wake State

The characteristic wake states of a cylinder undergoing forced sinusoidal oscillations transverse to the free-stream are studied by simultaneously measuring the structure of the near wake and the forces on the cylinder. The wake exhibits two distinctly different wake states. The transition between these states corresponds to a large discontinuous change in the phase of both the total and vortex forces on the cylinder, as well as the mode and phase of vortex shedding. Over the range of flow and oscillation parameters studied the vortex lift and drag phases collapse towards values that depend primarily on wake state. This is in contrast with the phase of the total lift force, which varied significantly with both A/D and Re.

scholarly journals Very Large-Eddy Simulations of the Flow Past an Oscillating Cylinder at a Subcritical Reynolds Number

2020 ◽  
Vol 10 (5) ◽  
pp. 1870
Author(s):  
Zhongying Xiong ◽  
Xiaomin Liu
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Lift Coefficient ◽  
Vortex Pair ◽  
Excitation Amplitude ◽  
Oscillating Cylinder ◽  
Flow Past ◽  
Large Eddy ◽  
Lift And Drag ◽  
Strong Vortex

This work focuses on flow past a circular cylinder at a subcritical Reynolds number. Although this classical study has been a concern for many years, it is still a challenging task due to the complexity of flow characteristics. In this paper, a high-efficiency very large-eddy simulation method is adopted and verified in order to handle the oscillating boundary. A series of numerical simulations are conducted to investigate the transient flow around the oscillating cylinder. The results show that the vortex shedding mode varies with an increase in the excitation amplitude and the excitation frequency. Vortex shedding is a lasting process under the condition of a low excitation amplitude that leads to irregular fluctuations of the lift and drag coefficients. For a vortex shedding mode that exhibits a strong vortex pair and a weak vortex pair or a weak single vortex, the temporal evolution of the lift coefficient of the oscillating cylinder shows irregular ”jumping” at a specific time per cycle corresponding to the shedding of the strong vortex pair. The vortex shedding mode and the frequency and time of the vortex shedding co-determine the temporal evolutions of the lift and drag coefficient.

A numerical study of an inline oscillating cylinder in a free stream

2011 ◽  
Vol 688 ◽  
pp. 551-568 ◽  
Author(s):  
Justin S. Leontini ◽  
David Lo Jacono ◽  
Mark C. Thompson
Keyword(s):  
Vortex Shedding ◽  
Free Stream ◽  
Numerical Study ◽  
Dynamic Responses ◽  
Sinusoidal Oscillations ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Quasiperiodic Oscillations ◽  
Fixed Cylinder ◽  
Stream Direction

AbstractSimulations of a cylinder undergoing externally controlled sinusoidal oscillations in the free stream direction have been performed. The frequency of oscillation was kept equal to the vortex shedding frequency from a fixed cylinder, while the amplitude of oscillation was varied, and the response of the flow measured. With varying amplitude, a rich series of dynamic responses was recorded. With increasing amplitude, these states included wakes similar to the Kármán vortex street, quasiperiodic oscillations interleaved with regions of synchronized periodicity (periodic on multiple oscillation cycles), a period-doubled state and chaotic oscillations. It is hypothesized that, for low to moderate amplitudes, the wake dynamics are controlled by vortex shedding at a global frequency, modified by the oscillation. This vortex shedding is frequency modulated by the driven oscillation and amplitude modulated by vortex interaction. Data are presented to support this hypothesis.

Aspects of Shear Layer Unsteadiness in a Three-Dimensional Supersonic Wake

2005 ◽  
Vol 127 (6) ◽  
pp. 1085-1094 ◽  
Author(s):  
Alan L. Kastengren ◽  
J. Craig Dutton
Keyword(s):  
Shear Layer ◽  
Stream Flow ◽  
Free Stream ◽  
Angle Of Attack ◽  
Three Dimensional ◽  
Base Flow ◽  
Recirculation Region ◽  
Side View ◽  
Near Wake ◽  
Supersonic Wake

The near wake of a blunt-base cylinder at 10° angle-of-attack to a Mach 2.46 free-stream flow is visualized at several locations to study unsteady aspects of its structure. In both side-view and end-view images, the shear layer flapping grows monotonically as the shear layer develops, similar to the trends seen in a corresponding axisymmetric supersonic base flow. The interface convolution, a measure of the tortuousness of the shear layer, peaks for side-view and end-view images during recompression. The high convolution for a septum of fluid seen in the middle of the wake indicates that the septum actively entrains fluid from the recirculation region, which helps to explain the low base pressure for this wake compared to that for a corresponding axisymmetric wake.

Numerical Investigation of Flow Around Bluff Bodies

1998 ◽  
Vol 14 (3) ◽  
pp. 153-159 ◽  
Author(s):  
Chou-Jiu Tsai ◽  
Ger-Jyh Chen
Keyword(s):  
Vortex Shedding ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Bluff Bodies ◽  
Near Wake ◽  
Navier Stokes Equations ◽  
Physical Description ◽  
Geometrical Shapes ◽  
Flow Phenomena ◽  
Volume Method

ABSTRACTIn this study, fluid flow around bluff bodies are studied to examine the vortex shedding phenomenon in conjuction with the geometrical shapes of these vortex shedders. These flow phenomena are numerically simulated. A finite volume method is employed to solve the incompressible two-dimensional Navier-Stokes equations. Thus, quantitative descriptions of the vortex shedding phenomenon in the near wake were made, which lead to a detailed description of the vortex shedding mechanism. Streamline contours, figures of lift coefficent, and figures of drag coefficent in various time, are presented, respectively, for a physical description.

2D and 2.5D Numerical Simulations for Vortex-Induced Vibration (VIV) of a 1.5:1 Rectangular Cylinder

2021 ◽  
Author(s):  
Bowen Yan ◽  
Yangjin Yuan ◽  
Dalong Li ◽  
Ke Li ◽  
Qingshan Yang ◽  
...  
Keyword(s):  
Wind Speed ◽  
Numerical Simulations ◽  
Phase Difference ◽  
Vortex Shedding ◽  
Lift Force ◽  
Small Scale ◽  
Aerodynamic Damping ◽  
Displacement Response ◽  
Wind Speeds ◽  
Rectangular Cylinder

The semi-periodic vortex-shedding phenomenon caused by flow separation at the windward corners of a rectangular cylinder would result in significant vortex-induced vibrations (VIVs). Based on the aeroelastic experiment of a rectangular cylinder with side ratio of 1.5:1, 2-dimensional (2D) and 2.5-dimensional (2.5D) numerical simulations of the VIV of a rectangular cylinder were comprehensively validated. The mechanism of VIV of the rectangular cylinder was in detail discussed in terms of vortex-induced forces, aeroelastic response, work analysis, aerodynamic damping ratio and flow visualization. The outcomes showed that the numerical results of aeroelastic displacement in the cross-wind direction and the vortex-shedding procedure around the rectangular cylinder were in general consistence with the experimental results by 2.5D numerical simulation. In both simulations, the phase difference between the lift and displacement response increased with the reduced wind speed and the vortex-induced resonance (VIR) disappeared at the phase difference of approximately 180∘. The work done by lift force shows a close relationship with vibration amplitudes at different reduced wind speeds. In 2.5D simulations, the lift force of the rectangular cylinder under different wind speeds would be affected by the presence of small-scale vortices in the turbulence flow field. Similarly, the phase difference between lift force and displacement response was not a constant with the same upstream wind speed. Aerodynamic damping identified from the VIV was mainly dependent on the reduced wind speed and negative damping ratios were revealed at the lock-in regime, which also greatly influenced the probability density function (PDF) of wind-induced displacement.

An Experimental Investigation of the Wake of an Axisymmetric Body with a Slanted Base

1983 ◽  
Vol 34 (1) ◽  
pp. 24-45 ◽  
Author(s):  
X.J. Xia ◽  
P.W. Bearman
Keyword(s):  
Drag Coefficient ◽  
Vortex Shedding ◽  
Free Stream ◽  
Sudden Change ◽  
Base Pressure ◽  
Wake Flow ◽  
Main Body ◽  
Angle Of Incidence ◽  
Slant Angle ◽  
Free Stream Turbulence

SummaryThe effect of base slant on the base pressure distribution, drag coefficient and vortex shedding characteristics of a model consisting of an axisymmetric main body with an ellipsoidal nose have been investigated for three fineness ratios; 3, 6 and 9. A sudden change in the drag coefficient and separated flow pattern is observed at a critical slant angle (for constant incidence) or at a critical angle of incidence (for a constant base slant angle). The tests confirm that the value of the maximum drag coefficient is extremely sensitive to angle of incidence. Measurements of the frequency of vortex shedding are presented and the structure of the wake is investigated using smoke visualization and hot-wire correlation measurements. The wake is found to be far less stable than that from a two-dimensional bluff body and the vortex structures are sometimes in-phase and sometimes out of phase across the wake. The effect of free-stream turbulence on this family of body shapes is observed to be different to that on three-dimensional blunt-faced bluff bodies. Free-stream turbulence is found to have a minimal effect on base pressure for slant angles giving a recirculating type near wake flow. When longitudinal vortices are present the addition of free-stream turbulence slightly reduces the magnitude of the peak suctions recorded on the base but has little effect on base drag.

Two- and Three-Dimensional Simulations of the Flow Around a Cylinder Fitted With Strakes

2012 ◽  
Author(s):  
Bruno S. Carmo ◽  
Rafael S. Gioria ◽  
Ivan Korkischko ◽  
Cesar M. Freire ◽  
Julio R. Meneghini
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Free Stream ◽  
Three Dimensional ◽  
The Body ◽  
Vortex Wake ◽  
Two Dimensional ◽  
Flow Around A Cylinder ◽  
Three Dimensional Simulations ◽  
Angle Of Rotation

Two- and three-dimensional simulations of the flow around straked cylinders are presented. For the two-dimensional simulations we used the Spectral/hp Element Method, and carried out simulations for five different angles of rotation of the cylinder with respect to the free stream. Fixed and elastically-mounted cylinders were tested, and the Reynolds number was kept constant and equal to 150. The results were compared to those obtained from the simulation of the flow around a bare cylinder under the same conditions. We observed that the two-dimensional strakes are not effective in suppressing the vibration of the cylinders, but also noticed that the responses were completely different even with a slight change in the angle of rotation of the body. The three-dimensional results showed that there are two mechanisms of suppression: the main one is the decrease in the vortex shedding correlation along the span, whilst a secondary one is the vortex wake formation farther downstream.

Experiments on the flow past an inclined disk

1967 ◽  
Vol 29 (4) ◽  
pp. 691-703 ◽  
Author(s):  
J. R. Calvert
Keyword(s):  
Vortex Shedding ◽  
Free Stream ◽  
Stream Velocity ◽  
Length Scale ◽  
Angle Of Incidence ◽  
Axially Symmetric ◽  
Periodic Motions ◽  
Reference Velocity ◽  
Shedding Frequency ◽  
A Chain

The wake of a disk at an angle to a stream contains marked periodic motions which arise from the regular shedding of vortices from the trailing edge. The vortices are in the form of a chain of irregular rings, each one linked to the succeeding one, and they move downstream at about 0·6 of free-stream velocity. The prominence of the vortex shedding increases as the angle of incidence (measured from the normal) increases up to at least 50°. The shedding frequency increases with the angle of incidence, but by a suitable choice of reference velocity and length scale, may be described by a wake Strouhal number which has the constant value 0·21 for all angles of incidence above zero, up to at least 40°.Axially-symmetric bodies at zero incidence shed vortices in a similar manner, except that the orientation of the plane of vortex shedding is not fixed and varies from time to time.

Simulation of Solid-Fluid Interactions on Cartesian Grids

2000 ◽  
Author(s):  
H. S. Udaykumar ◽  
R. Mittal ◽  
P. Rampunggoon
Keyword(s):  
Vortex Shedding ◽  
Free Stream ◽  
Numerical Technique ◽  
Fractional Step ◽  
Flow Solver ◽  
Flow Equations ◽  
Poisson Equations ◽  
Lagrangian Framework ◽  
Sharp Interfaces ◽  
Immersed Boundaries

Abstract We present a numerical technique for computing flowfields around moving solid boundaries immersed in flows on fixed meshes. The mixed Eulerian-Lagrangian framework treats the immersed boundaries as sharp interfaces and a finite volume formulation for the flow solver allows boundary conditions at the moving surfaces to be exactly applied. A second-order accurate spatial and temporal discretization is employed with a fractional-step scheme for solving the flow equations. A multigrid accelerator for the pressure Poisson equations has been developed to apply in the presence of multiple embedded solid regions on the mesh. We validate the numerics by comparing against experimental and numerical results on two problems: 1) The flow in a channel with a moving indentation in one wall and 2) The dynamics of vortex shedding from a cylinder oscillating in the free-stream.

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