On the Streamwise Oscillations of Freely Vibrating Cylinder Near a Stationary Plane Wall in Steady Flow

2016 ◽  
Author(s):  
Zhong Li ◽  
Weigang Yao ◽  
Rajeev K. Jaiman ◽  
Boo Cheong Khoo
Keyword(s):  
Energy Transfer ◽  
Circular Cylinder ◽  
Vibration Frequency ◽  
Vibration Amplitude ◽  
Hydrodynamic Forces ◽  
Plane Wall ◽  
The Mean ◽  
Lock In ◽  
Wall Proximity ◽  
Near Wall

A partitioned iterative scheme based on Petrov-Galerkin formulation [1] has been employed for simulating flow past a freely vibrating circular cylinder placed in proximity to a stationary plane wall in both two-dimension (2D) and three-dimension (3D). In the first part of this work, effects of wall proximity on the vortex-induced vibration (VIV) of an elastically mounted circular cylinder with two degree-of-freedom (2-DoF) are systematically studied in 2D by investigating the hydrodynamic forces acting on the cylinder, the vibration amplitudes, the phase differences between the forces and displacements, the response frequencies as well as the vortex shedding dynamics. For that purpose, a careful comparison has been established for the isolated and near-wall cylinders, in which the gap ratio, e/D (where e denotes the gap between the cylinder and the wall and D denotes the diameter of the cylinder), is set to be 0.9, at Re = 200. Our 2D simulations have revealed that larger streamwise vibration amplitude and smaller streamwise vibration frequency can be observed in VIV of the near-wall cylinder compared to its isolated counterpart. We then focus on the explanation of the enhanced streamwise vibration amplitude when the cylinder is placed in the vicinity of the plane wall. It is found that the wall proximity largely amplifies the streamwise vibration amplitude due to net energy transfer from the fluid to the cylinder in the pre-lock-in region as well as the initial branch of the lock-in region, while reduces the streamwise vibration frequency to the level of the transverse vibration frequency. In the second part, the main focus of this article, following Tham et al. (2015) [2] where 2D results were systematically reported, we perform 3D simulations of VIV of a circular cylinder for both isolated and near-wall cases (e/D = 0.9) at Re = 1000 to compare the hydrodynamic forces and vibration characteristics in 3D with the results corresponding to the 2D study. We show that wall proximity effects on VIV are also pronounced in 3D with the following observations: (1) the wall proximity increases the mean lift to a lesser extent compared to 2D, while also enhances the mean drag unlike in 2D; (2) the wall proximity enhances the streamwise oscillation as well owing to a combined effect of increased drag force together with energy transfer from fluid to structure as in 2D; (3) in terms of the flow field, the wall proximity increases the wavelength of streamwise vorticity blob; and (4) similarly with the mechanism of vortex suppression in 2D, wall boundary layer vorticity strongly strengthens the negative vorticity shed from upper surface of cylinder, stretching and suppressing the positive vorticity shed from the bottom surface of cylinder.

Two-Dimensional Numerical Simulations of Wall Proximity Effect on Cylinders

2015 ◽  
Author(s):  
Zhong Li ◽  
Rajeev K. Jaiman ◽  
Mun Yew Daniel Tham ◽  
Boo Cheong Khoo
Keyword(s):  
Circular Cylinder ◽  
Proximity Effects ◽  
Displacement Amplitude ◽  
Plane Boundary ◽  
Transverse Displacement ◽  
Two Dimensional ◽  
Immersed Interface Method ◽  
The Mean ◽  
Wall Proximity ◽  
Near Wall

In the oil and offshore industry, it is a common phenomenon that subsea pipelines placed on or in the proximity of the seabed are exposed to underwater waves and currents. Free spanning in sections along the length of pipeline frequently results from the erosion of sediments or the irregular terrain. This scenario can be modelled by a much more simplified set-up, where a circular cylinder situated near a plane wall is subjected to the oncoming flows. In this case, unlike the well-studied isolated cylinder, the hydrodynamic forces exerting on the near-wall cylinder will depend largely upon on the gap between the wall and the cylinder itself. In this work, flows around a stationary and a freely vibrating two-dimensional circular cylinder near a plane boundary are numerically simulated using the Immersed Interface Method (IIM) and Finite Element Method (FEM) with Arbitrary Lagrangian-Eulerian (ALE) approach, respectively. In the case of a stationary cylinder, instead of a fixed wall, a moving wall with no-slip boundary is considered in order to avoid the complex involvement of the boundary layer and to focus only on the shear-free wall proximity effects in evaluating the lift and drag forces in the low Reynolds number regime (Re ≤ 200), with the aim of validating our IIM solver since it is the first time to apply IIM in solving flows past a near-wall cylinder. The gap ratio e/D is typically taken from 0.1 to 2.0 in this part of studies, where e denotes the gap between the cylinder and the wall and D denotes the diameter of the cylinder. The key findings are that the mean drag coefficient increases and peaks at e/D = 0.5 with the increase of e/D and keeps decreasing from e/D = 0.5 to e/D = 2.0, while the mean lift coefficient decreases monotonically with the increase of e/D. In the case of the freely vibrating cylinder in both transverse and in-line directions, the fixed wall is used to include the shear-layer effect from the bottom wall in considering the near-wall vortex-induced vibration (VIV) by using FEM with ALE approach. It can be concluded from our observations that when the cylinder is brought closer to the wall from e/D = 10.0 to e/D = 0.75, the peak transverse displacement amplitude decreases, while the peak in-line displacement amplitude increases, by greater than 20 times that of an isolated cylinder.

Pressure-fluctuation measurements on an oscillating circular cylinder

1979 ◽  
Vol 91 (4) ◽  
pp. 661-677 ◽  
Author(s):  
P. W. Bearman ◽  
I. G. Currie
Keyword(s):  
Circular Cylinder ◽  
Flow Model ◽  
Free Stream ◽  
Pressure Fluctuations ◽  
The Body ◽  
The Mean ◽  
Simple Potential ◽  
Lock In ◽  
Potential Flow Model ◽  
Good Agreement

Measurements are presented of the fluctuating pressure recorded at a point 90° from the mean position of the forward stagnation point on a circular cylinder oscillating in a water flow. The aspect ratio of the cylinder was 9·5 and the turbulence level in the free-stream was 5·5%. The cylinder Reynolds number was 2·4 × 104 and the cylinder was forced to oscillate transverse to the main flow at amplitudes up to 1·33 cylinder diameters. The reduced velocity was varied over the range 3–18 and the experiments spanned the vortex-shedding lock-in range. Measurements of phase difference between pressure and displacement show that the maximum out-of-phase lift force occurs at an amplitude of about half a diameter. Good agreement is found between measurements on forced and freely oscillating cylinders. A simple potential-flow model gives reasonable predictions of the pressure fluctuations at the body frequency and at twice the body frequency at reduced velocities away from lock-in.

Phase jump and energy transfer of forced oscillating circular cylinder in uniform flow

2016 ◽  
Vol 231 (2) ◽  
pp. 496-510
Author(s):  
Guoqiang Tang ◽  
Lin Lu ◽  
Ming Zhao ◽  
Mingming Liu ◽  
Zhi Zong
Keyword(s):  
Reynolds Number ◽  
Energy Transfer ◽  
Circular Cylinder ◽  
Phase Difference ◽  
Uniform Flow ◽  
Phase Jump ◽  
Fluid Forces ◽  
Special Cases ◽  
Lock In ◽  
Transfer Direction

The phase jump, energy transfer, and the associated vortex shedding modes of a circular cylinder undergoing forced oscillation normal to the incoming uniform flow are investigated numerically at Reynolds number ( Re) of 200. The dependence of the fluid forces on the non-dimensional oscillating amplitude A* =  A/ D ∈ [0.1, 0.6] and frequency f* =  fe/ fs ∈ [0.5, 2.0] is examined, where A is the oscillating amplitude, D is the cylinder diameter, fe is the cylinder oscillating frequency, and fs is the Strouhal frequency of fixed cylinder at the same Reynolds number, respectively. The lock-in region is identified by the combination of Fourier analysis and Lissajous phase diagram. The phase difference between displacement and lift fluctuation and the energy transfer between fluid and structure are discussed. Within the lock-in region, a jump in the phase difference is found to occur in the cases with A* = 0.5 and 0.55 without a wake mode transition. The numerical results reveal that the appearance of the phase jump is consistent with the reversal of the energy transfer direction. For the special cases of A* = 0.5 and 0.55, changes in the sign of energy transfer are observed, while no reversal of energy transfer is observed at other amplitudes. The energy transfer direction is either from fluid to cylinder when A* ∈ [0.1, 0.4] or from cylinder to fluid when A* ≥ 0.6. It is confirmed that the energy transfer between fluid and cylinder is not only dependent on cylinder oscillating frequency but also on cylinder oscillating amplitude.

scholarly journals Fluid-Structure Energy Transfer of a Tensioned Beam Subject to Vortex-Induced Vibrations in Shear Flow

2011 ◽  
Author(s):  
Remi Bourguet ◽  
Michael S. Triantafyllou ◽  
Michael Tognarelli ◽  
Pierre Beynet
Keyword(s):  
Energy Transfer ◽  
Shear Flow ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Structural Vibrations ◽  
Fluid Structure ◽  
Vortex Induced Vibrations ◽  
Linear Shear ◽  
Structural Responses ◽  
Lock In

The fluid-structure energy transfer of a tensioned beam of length to diameter ratio 200, subject to vortex-induced vibrations in linear shear flow, is investigated by means of direct numerical simulation at three Reynolds numbers, from 110 to 1,100. In both the in-line and cross-flow directions, the high-wavenumber structural responses are characterized by mixed standing-traveling wave patterns. The spanwise zones where the flow provides energy to excite the structural vibrations are located mainly within the region of high current where the lock-in condition is established, i.e. where vortex shedding and cross-flow vibration frequencies coincide. However, the energy input is not uniform across the entire lock-in region. This can be related to observed changes from counterclockwise to clockwise structural orbits. The energy transfer is also impacted by the possible occurrence of multi-frequency vibrations.

Lock-in regions of laminar flows over a streamwise oscillating circular cylinder

2018 ◽  
Vol 858 ◽  
pp. 315-351 ◽  
Author(s):  
Ki-Ha Kim ◽  
Jung-Il Choi
Keyword(s):  
Circular Cylinder ◽  
Aerodynamic Force ◽  
Lift Coefficient ◽  
Lower Boundary ◽  
Laminar Flows ◽  
Velocity Range ◽  
Frequency Range ◽  
Vortex Pattern ◽  
Moving Cylinder ◽  
Lock In

In this paper, flow over a streamwise oscillating circular cylinder is numerically simulated to examine the effects of the driving amplitude and frequency on the distribution of the lock-in regions in laminar flows. At $Re=100$, lock-in is categorized according to the spectral features of the lift coefficient as two different lock-in phenomena: harmonic and subharmonic lock-in. These lock-in phenomena are represented as maps on the driving amplitude–frequency plane, which have subharmonic lock-in regions and two harmonic lock-in regions. The frequency range of the subharmonic region is shifted to lower frequencies with increasing amplitude, and the lower boundary of this subharmonic region is successfully predicted. A symmetric harmonic region with a symmetric vortex pattern is observed in a certain velocity range for a moving cylinder. Aerodynamic features induced by different flow patterns in each region are presented on the driving amplitude–frequency plane. The lock-in region and aerodynamic features at $Re=200$ and $40$ are compared with the results for $Re=100$. A subharmonic region and two harmonic regions are observed at $Re=200$, and these show the same features as for $Re=100$ at a low driving amplitude. Lock-in at $Re=40$ also shows one subharmonic region and two harmonic regions. However, compared with the $Re=100$ case, the symmetric harmonic lock-in is dominant. The features of aerodynamic force at $Re=200$ and $40$ are represented on a force map, which shows similar characteristics in corresponding regions for the $Re=100$ case.

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