Unsteady Force Measurements on a Responding Circular Cylinder in the Wake of an Upstream Cylinder

2007 ◽  
Author(s):  
Gustavo R. S. Assi ◽  
Peter W. Bearman ◽  
Julio R. Meneghini
Keyword(s):  
Circular Cylinders ◽  
Force Measurements ◽  
Flow Induced Vibration ◽  
Constant Rate ◽  
Unsteady Force ◽  
Low Mass ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Low Mass Ratio ◽  
Flow Interference

This paper presents force measurements during flow-induced vibration of a pair of circular cylinders with low mass ratio (m* = 2.0) and low damping (ζ = 0.7%) aligned in a tandem arrangement. A particular case with a gap of 3 diameters centre to centre is used to examine flow-interference mechanisms occurring on a downstream cylinder, free to oscillate only in the transverse direction. The Reynolds number varies within the range 1500 < Re < 20000. A cylinder immersed in the wake of another can develop flow-induced oscillations persisting for a large range of reduced velocities. Oscillations are observed for reduced velocities, based on cylinder natural frequency measured in air, as high as 35. Apparently, the amplitude of oscillation is reaching a level of saturation of about 1.5 diameters, while the frequency of vibration is increasing at an approximate constant rate. As reduced velocity is increased two regimes of flow-induced vibration are observed: first vortex-induced vibration and then a wake-induced vibration regime. In addition, the presence of the second cylinder affects the dynamics of the upstream wake, but it is found not to synchronize the vortex shedding frequency of the upstream cylinder for the second regime of oscillations.

Flow-Induced Streamwise Vibration of a Flexibly-Mounted Cantilevered Cylinder in Steady and Pulsating Crossflow

2009 ◽  
Author(s):  
Joseph Sherwood ◽  
Jonathan Dusting ◽  
Efstathios Konstantinidis ◽  
Stavroula Balabani
Keyword(s):  
Steady Flow ◽  
Excitation Frequency ◽  
Reynolds Numbers ◽  
Pulsation Frequency ◽  
Plate Spring ◽  
Low Mass ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Low Mass Ratio ◽  
Fixed Cylinder

This paper describes an experimental study of the response of a freely vibrating cylinder with low mass ratio and high damping to steady and pulsating crossflow for Reynolds numbers in the range 120–2900. A rigid circular cylinder was cantilevered by means of a plate spring allowing it to oscillate in the stream-wise direction only. A camera-based technique was employed for tracking the cylinder vibration while the wake fluctuations were measured by a laser-Doppler system. The results show that the forced excitation from pulsating flow can take over control of the wake and/or the cylinder oscillations in a complex manner. The overall response depends strongly on two main parameters: the ratios of the pulsation frequency to the structural frequency and to the vortex shedding frequency from a fixed cylinder in steady flow. When the excitation frequency from both the wake and the external pulsation coincided with the natural frequency of the structure, the r.m.s. amplitude of the cylinder vibration increased up to 400% compared to that for the same reduced velocity in steady flow. In this case, maximum end displacements exceeded 35% of the cylinder diameter.

Phenomena of vortex shedding and flow interference of three cylinders in different equilateral arrangements

1988 ◽  
Vol 196 ◽  
pp. 1-26 ◽  
Author(s):  
K. Lam ◽  
W. C. Cheung
Keyword(s):  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Injection Technique ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Visualization Experiments ◽  
Flow Interference ◽  
Bistable Flow

This paper describes how the flows around three equal circular cylinders arranged in an equilateral-triangular manner interact at different angles of incidence α and spacing ratios l/d. Some vortex-shedding-frequency data evaluated from flow visualization experiments conducted at Reynolds numbers of 2.1 × 103 and 3.5 × 103, based on the diameter of a single cylinder, using a dye -injection technique, are presented. In order to provide additional insight to the understanding of the flow structure around this particular cylinder array, some photographs indicating the typical flow patterns for various arrangements are also presented. The investigation indicates that the flows interact in a complex fashion for spacing ratios smaller than 2.29 and it also reveals that, at this range of spacing ratios and at α = 0°, bistable flow characteristic exists. Moreover, for l/d approximately smaller than 4.65 there always exists an angle at which the vortex shedding behind an upstream cylinder is suppressed by a nearest downstream cylinder. This angle is found not to remain constant but increases as the spacing ratio increases. For illustration and comparisons, some numerical results obtained from the application of the surface-vorticity method have also been presented.

Flow-Induced Vibration (FIV) and Hydrokinetic Power Conversion of Two Staggered, Low Mass-Ratio Cylinders, With Passive Turbulence Control in the TrSL3 Flow Regime (2.5×104

2017 ◽  
Author(s):  
Wanhai Xu ◽  
Chunning Ji ◽  
Hai Sun ◽  
Wenjun Ding ◽  
Michael M. Bernitsas
Keyword(s):  
Flow Regime ◽  
Total Power ◽  
Mass Ratio ◽  
Flow Induced Vibration ◽  
Turbulence Control ◽  
Hydrokinetic Energy ◽  
Staggered Arrangement ◽  
Low Mass ◽  
Low Mass Ratio ◽  
Passive Turbulence Control

Flow-induced vibration (FIV), primarily vortex-induced vibrations (VIV) and galloping have been used effectively to convert hydrokinetic energy to electricity in model-tests and field-tests by the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan. The developed device, called VIVACE (VIV for Aquatic Clean Energy), harnesses hydrokinetic energy from river and ocean flows. One of the methods used to improve its efficiency of harnessed power efficiency is Passive Turbulence Control (PTC). It is a turbulence stimulation method that has been used to alter FIV of a cylinder in a steady flow. FIV of elastically mounted cylinders with PTC differs from the oscillation of smooth cylinders in a similar configuration. Additional investigation of the FIV of two elastically mounted circular cylinders in staggered arrangement with a low mass ratio in the TrSL3 flow-regime is required and is contributed by this paper. A series of experimental studies on FIV of two PTC cylinders in staggered arrangement were carried out in the recirculating water channel of MRELab. The two cylinders were allowed to oscillate in the transverse direction to the oncoming fluid flow. Cylinders tested have, diameter D = 8.89cm, length L = 0.895m and mass ratio m* = 1.343. The Reynolds number was in the range of 2.5×104<Re<1.2×105, which is a subset of the TrSL3 flow-regime. The center-to-center longitudinal and transverse spacing distances were T/D = 2.57 and S/D = 1.0, respectively. The spring stiffness values were in the range of 400<K<1200N/m. The values of harnessing damping ratio tested were ζharness = 0.04, 0.12, 0.24. For the values tested, the experimental results indicate that the response of the 1st cylinder is similar to a single cylinder; however more complicated vibration of the 2nd cylinder is observed. In addition, the oscillation system of two cylinders with stiffer spring and higher ζharness could initiate total power harness at a larger flow velocity and harness much higher power. These findings are very meaningful and important for hydrokinetic energy conversion.

An Experimental Study on Flow Induced Vibration of a Circular Cylinder in Shear Flow

2010 ◽  
Author(s):  
Ming Huei Yu ◽  
Yi-hsin Wu
Keyword(s):  
Circular Cylinder ◽  
Shear Flow ◽  
Test Section ◽  
Unit Length ◽  
Large Mass ◽  
Elastic Vibration ◽  
Mass Ratio ◽  
Flow Induced Vibration ◽  
Low Mass ◽  
Low Mass Ratio

The vibrations of a circular cylinder in both uniform and shear flows are investigated experimentally. For the experimental investigation, a low speed water tunnel was designed and built to provide either uniform or shear flow in the test section, depending on the upstream flow management. In the test section, a circular tube of various materials can be flexibly mounted for vibration testing. Two accelerators were carefully installed inside the tube so that one accelerator is sensitive to the cylinder vibration in the streamwise direction only, and the other in the cross-stream direction. The vibration amplitudes of the cylinder in the streamwise and cross-stream directions were simultaneously measured by the two accelerators, and recorded by a two-channel data acquisition system. The orbits of the cylinder motion can be drawn from the data. Experiments were conduced at various mass ratios (the ratio of the cylinder mass per unit length to its buoyancy force) and shear parameters (the non-dimensional velocity gradient of the approaching fluid flow to the cylinder). By analyzing the orbits and amplitude diagrams, it is found that both the shear parameter and mass ratio have profound effects on the cylinder vibration. The orbits of the cylinder in uniform flow are symmetric while they are asymmetric in shear flow. Vibration amplitude as a function of reduced velocity illustrates that the cylinder in uniform or shear flow does not vibrate at low reduced velocities but vibrate significantly beginning at the reduced velocity around 5, initiated by vortex-induced instability. At high reduced velocity, the circular cylinder in shear flow still vibrates at significant amplitude, an evidence of fluid elastic vibration. It is also shown by the amplitude diagrams that low mass ratio promotes the cylinder’s vibration while large mass ratio reduces the vibration.

The Spanwise Dependence of Vortex-Shedding From Yawed Circular Cylinders

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
James D. Hogan ◽  
Joseph W. Hall
Keyword(s):  
Vortex Shedding ◽  
Flow Direction ◽  
Rapid Decrease ◽  
Circular Cylinders ◽  
Mean Flow ◽  
Independence Principle ◽  
Simultaneous Measurements ◽  
Vortex Shedding Frequency ◽  
The Mean ◽  
Shedding Frequency

Simultaneous measurements of the fluctuating wall pressure along the cylinder span were used to examine the spanwise characteristics of the vortex-shedding for yaw angles varying from α=60 deg to α=90 deg. The Reynolds number based on the diameter of the cylinder was 56,100. The results indicate that yawing the cylinder to the mean flow direction causes the vortex-shedding in the wake to become more disorderly. This disorder is initiated at the upstream end of the cylinder and results in a rapid decrease in correlation length, from 3.3D for α=90 deg to 1.1D for α=60 deg. The commonly used independence principle was shown to predict the vortex-shedding frequency reasonably well along the entire cylinder span for α>70 deg, but did not work as well for α=60 deg.

A Numerical Study of Geometrical Effects on the Strouhal Number of a Circular Cylinder

2008 ◽  
Author(s):  
Farzan Kazemifar ◽  
Mehdi Molai ◽  
Bahar Firoozabadi ◽  
Goodarz Ahmadi
Keyword(s):  
Circular Cylinder ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Numerical Study ◽  
Circular Cylinders ◽  
Percentage Reduction ◽  
Blade Angle ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Geometrical Effects

In this paper, reducing the Strouhal number of a circular cylinder is studied numerically. Two-dimensional numerical simulations of flow over a normal circular cylinder and various modified circular cylinders are carried out using FLUENT® soft ware. Two small blades are attached to a circular cylinder and the effects of variation of the blades length and the blade angle are studied numerically. The blade angle is chosen 2α = 0°, 30°, 90°, 120° and 150°. The blades length is chosen l/d = 0.125, 0.25, 0.375. Effects of blade angles and blade lengths were studied for both 2α = 0° and 150°. Results show that increasing in blade lengths decreases the Strouhal number. Moreover, as the blade angle was increased from zero to 90°, the percentage reduction in Strouhal number decreased; however, as the blade angle was further increased from 90° to 150°, the percentage reduction in Strouhal number increased. Although the modifications studied here decrease the vortex shedding frequency they make the vortices shed from the cylinder farther and stronger hence increasing the magnitude of the fluctuating forces.

Local Force Measurements on Finite-Span Cylinders in a Cross-Flow

1987 ◽  
Vol 109 (2) ◽  
pp. 136-143 ◽  
Author(s):  
V. K. Sin ◽  
Ronald M. C. So
Keyword(s):  
Free Stream ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Two Dimensional ◽  
Force Measurements ◽  
Unsteady Forces ◽  
Free Stream Turbulence ◽  
Finite Span ◽  
Present Technique ◽  
Unsteady Force

A technique employing a three-axis piezoelectric load cell is developed to measure local unsteady forces induced on cylinders placed in a cross flow. Verification of the technique is carried out with a two-dimensional circular cylinder. All measurements are made at a Reynolds number of ∼4.8 × 104 and a free-stream turbulence of ∼1.5 percent. The local two-dimensional unsteady lift measurement is found to be in excellent agreement with spanwise-averaged data reported in the literature, thereby validating the feasibility of the present technique. Steady and unsteady force measurements on finite-span circular cylinders are reported and compared with available data in the literature.

Flow-Induced Vibration of a Cylinder in the Wake of Another of Smaller Diameter

2014 ◽  
Author(s):  
Md. Mahbub Alam ◽  
An Ran ◽  
Yu Zhou
Keyword(s):  
Circular Cylinder ◽  
Free Stream ◽  
Cross Flow ◽  
Induced Response ◽  
Stream Velocity ◽  
Flow Induced Vibration ◽  
Cylinder Diameter ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

This paper presents cross-flow induced response of a both-end-spring-mounted circular cylinder (diameter D) placed in the wake of a rigid circular cylinder of smaller diameter d. The cylinder vibration is constrained to the transverse direction. The cylinder diameter ratio d/D and spacing ratio L/d are varied from 0.2 to 1.0 and 1.0 to 5.5, respectively, where L is the distance between the center of the upstream cylinder to the forward stagnation point of the downstream cylinder. A violent vibration of the cylinder is observed for d/D = 0.2 ∼ 0.8 at L/d = 1.0, for d/D = 0.24 ∼ 0.6 at 1.0 < L/d ≤ 2.5, for d/D = 0.2 ∼ 0.4 at 2.5 < L/d ≤ 3.5, and for d/D = 0.2 at 3.5 < L/d ≤ 5.5, but not for d/D = 1.0. A smaller d/D generates vibration for a longer range of L/d. The violent vibration occurs at a reduced velocity Ur (=U∞/fnD, where U∞ is the free-stream velocity and fn the natural frequency of the cylinder system) beyond the vortex excitation regime (Ur ≥ 8) depending on d/D and L/d. Once the vibration starts to occur, the vibration amplitude increases rapidly with increasing Ur. It is further noted that the flow behind the downstream cylinder is characterized by two predominant frequencies, corresponding to the cylinder vibration frequency and the natural vortex shedding frequency of the cylinder, respectively. While the former persists downstream, the latter vanishes rapidly.

The locking-on of vortex shedding due to the cross-stream vibration of circular cylinders in uniform and shear flows

1976 ◽  
Vol 74 (4) ◽  
pp. 641-665 ◽  
Author(s):  
P. K. Stansby
Keyword(s):  
Reynolds Number ◽  
Shear Flow ◽  
Vortex Shedding ◽  
Shear Flows ◽  
Uniform Flow ◽  
Circular Cylinders ◽  
Stream Velocity ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
The Cross

The frequencies of vortex shedding from circular cylinders forced to oscillate transversely in low-turbulence uniform and shear flows were investigated. The stream velocity in the shear flow varied linearly with spanwise distance.In both flows the vortex shedding frequency locked on to the cylinder frequency and to submultiples of the cylinder frequency. In uniform flow the range of cylinder frequencies for locking-on was dependent on the amplitude of oscillation and Reynolds number. At the boundaries of locking-on at the cylinder frequency locked-on shedding was intermittent with unforced shedding and locking-on was accompanied by a change in wake width. At a particular cylinder frequency near mid-range it is conjectured that the wake width jumped from being greater to being less than that for the stationary cylinder. In shear flow the spanwise extent of locking-on at the cylinder frequency was explained by considering the uniform flow results and the inclination of shed vortices in shear flow. At the spanwise boundaries of this locking-on, locked-on cells were shed intermittently with unforced cells which were more stable in frequency than the corresponding cells for the stationary cylinder.

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