scholarly journals Effect of Gap Flow on the Characteristics of Flow-Around and Flow-Induced Vibration for Two Circular Cylinders with Roughness Strips

2019 ◽  
Vol 9 (17) ◽  
pp. 3587 ◽  
Author(s):  
Zuo-Mei Yang ◽  
Lin Ding ◽  
Qian-Yun Ye ◽  
Lin Yang ◽  
Li Zhang
Keyword(s):  
Strouhal Number ◽  
Circular Cylinders ◽  
Vibration Frequencies ◽  
Flow Induced Vibration ◽  
Force Coefficient ◽  
Wake Structure ◽  
Vortex Pattern ◽  
Gap Flow ◽  
Relationship Of ◽  
Main Factor

In order to understand the gap flow between two cylinders, the characteristics of flow around two stationary cylinders and the flow-induced vibration of two staggered cylinders with roughness strips are numerically studied. The lift–drag responses, Strouhal number (St) and wake structure of two stationary cylinders in tandem, as well as the vibration response and vortex pattern of two oscillating staggered cylinders are analyzed. The results indicate that the spacing dc of two stationary cylinders at which the gap flow can be observed is different for different Re, and dc is 3D when Re = 2000 and dc = 2.5D at Re = 6000~14,000. When the distance d = dc, the force coefficient and St of two cylinders increase sharply. For the two oscillating staggered cylinders, there is a critical reduced velocity Uc* = 7, which makes the amplitude magnitude relationship of the two cylinders change. With the change of the reduced velocity, the vibration frequencies of the two cylinders are consistent. When the staggered distance increases, the frequency difference of the two cylinders decreases. At the same inflow velocity, with the increase of staggered distance, a gap flow is formed between the two cylinders. When T > 0.6D and U* < 8, the gap flow becomes the main factor affecting the vibration of the two cylinders, which can be divided into the dominant region of gap flow.

scholarly journals Research on Flow-Induced Vibration and Energy Harvesting of Three Circular Cylinders with Roughness Strips in Tandem

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2977 ◽  
Author(s):  
Lin Ding ◽  
Qunfeng Zou ◽  
Li Zhang ◽  
Haibo Wang
Keyword(s):  
Reynolds Number ◽  
Energy Harvesting ◽  
Maximum Amplitude ◽  
Energy Conversion Efficiency ◽  
Circular Cylinders ◽  
Flow Induced Vibration ◽  
Number Range ◽  
Vortex Pattern ◽  
Simulation And Experiment ◽  
Vortex Patterns

The flow-induced vibration (FIV) of multiple cylinders is a common phenomenon in industry and nature. The FIV and energy harvesting of three circular cylinders in tandem are numerically studied by 2D-URANS simulations in Reynolds number range of 30,000 < Re < 105,000. Simulation results match well with experiments in the tested cases. Four branches of FIV are clearly captured in the amplitude and frequency ratio curves of the three cylinders with roughness, including initial branch of vortex-induced vibration (VIV), VIV upper branch, transition from VIV to galloping, and galloping. It is shown that the vortices from downstream cylinder are strongly disrupted and modified by vortices of upstream cylinder. The third cylinder is almost suppressed in VIV initial branch. The 2P vortex pattern is observed for the first cylinder in the VIV upper branch. For Re = 90,000 in the transition regime, the vortex patterns of the first and second cylinders are 2P + 4S and 2P + 2S, respectively. In the galloping branch, the shear layer motion is in synchronization with the motion of the cylinder, and the maximum amplitude of 2.8D is reached by the first cylinder. The total converted power of the three cylinders increases with U*water both in the simulation and experiment. For the three cylinders, the maximum power reaches up to 85.26 W with the increase of Reynolds number. The energy conversion efficiency is stable and higher than 35% in the starting region of VIV upper branch, and the maximum value of 40.41% is obtained when Re = 40,000.

CFD Modelling of Wake-Induced Vibration At Low Reynolds Number

CFD Letters ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 53-64
Author(s):  
Muhammad Ridhwaan Hassim ◽  
Mohd Azan Mohammed Sapardi ◽  
Nur Marissa Kamarul Baharin ◽  
Syed Noh Syed Abu Bakar ◽  
Muhammad Abdullah ◽  
...  
Keyword(s):  
Electrical Energy ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Flow Induced Vibration ◽  
Cfd Modelling ◽  
Force Coefficient ◽  
Low Reynolds ◽  
Harvesting Process ◽  
Fluid Behaviour

Flow-induced vibration is an enthralling phenomenon in the field of engineering. Numerous studies have been conducted on converting flow kinetic energy to electrical energy using the fundamental. Wake-induced vibration is one of the configurations used to optimise the generation of electricity. The results of the study on the effect of the gap between the multiple bluff bodies will provide insight into optimising the energy harvesting process. This study focuses on fluid behaviour and response behind two circular cylinders arranged in tandem when interacting with a fluid flow at low Reynolds numbers ranging from 200 to 1000. The study has been done on several gap lengths between the two cylinders, between 2D and 5D. The study was carried out numerically by using OpenFOAM. At Re = 1000, it is found that the gap length of 2.5D is optimal in terms of producing the highest lift force coefficient on the downstream circular cylinder.

Two-degree-of-freedom flow-induced vibration of two circular cylinders with constraint for different arrangements

2021 ◽  
Vol 225 ◽  
pp. 108806
Author(s):  
Qunfeng Zou ◽  
Lin Ding ◽  
Rui Zou ◽  
Hao Kong ◽  
Haibo Wang ◽  
...  
Keyword(s):  
Degree Of Freedom ◽  
Circular Cylinders ◽  
Flow Induced Vibration ◽  
Two Degree Of Freedom

Strouhal Number for VIV Excitation of Long Slender Structures

2018 ◽  
Author(s):  
Andrew E. Potts ◽  
Douglas A. Potts ◽  
Hayden Marcollo ◽  
Kanishka Jayasinghe
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Degrees Of Freedom ◽  
Measurement Techniques ◽  
Cross Flow ◽  
Degree Of Freedom ◽  
Circular Cylinders ◽  
Two Degrees Of Freedom ◽  
Shedding Frequency ◽  
Eddy Shedding

The prediction of Vortex-Induced Vibration (VIV) of cylinders under fluid flow conditions depends upon the eddy shedding frequency, conventionally described by the Strouhal Number. The most commonly cited relationship between Strouhal Number and Reynolds Number for circular cylinders was developed by Lienhard [1], whereby the Strouhal Number exhibits a consistent narrow band of about 0.2 (conventional across the sub-critical Re range), with a pronounced hump peaking at about 0.5 within the critical flow regime. The source data underlying this relationship is re-examined, wherein it was found to be predominantly associated with eddy shedding frequency about fixed or stationary cylinders. The pronounced hump appears to be an artefact of the measurement techniques employed by various investigators to detect eddy-shedding frequency in the wake of the cylinder. A variety of contemporary test data for elastically mounted cylinders, with freedom to oscillate under one degree of freedom (i.e. cross flow) and two degrees of freedom (i.e. cross flow and in-line) were evaluated and compared against the conventional Strouhal Number relationship. It is well established for VIV that the eddy shedding frequency will synchronise with the near resonant motions of a dynamically oscillating cylinder, such that the resultant bandwidth of lock-in exhibits a wider range of effective Strouhal Numbers than that reflected in the narrow-banded relationship about a mean of 0.2. However, whilst cylinders oscillating under one degree of freedom exhibit a mean Strouhal Number of 0.2 consistent with fixed/stationary cylinders, cylinders with two degrees of freedom exhibit a much lower mean Strouhal Number of around 0.14–0.15. Data supports the relationship that Strouhal Number does slightly diminish with increasing Reynolds Number. For oscillating cylinders, the bandwidth about the mean Strouhal Number value appears to remain largely consistent. For many practical structures in the marine environment subject to VIV excitation, such as long span, slender risers, mooring lines, pipeline spans, towed array sonar strings, and alike, the long flexible cylinders will respond in two degrees of freedom, where the identified difference in Strouhal Number is a significant aspect to be accounted for in the modelling of its dynamic behaviour.

Intrinsic features of flow past three square prisms in side-by-side arrangement

2017 ◽  
Vol 826 ◽  
pp. 996-1033 ◽  
Author(s):  
Qinmin Zheng ◽  
Md. Mahbub Alam
Keyword(s):  
Beat Frequency ◽  
Phase Relationship ◽  
Streamwise Velocity ◽  
Viscous Force ◽  
Phase Lag ◽  
Force Coefficient ◽  
Fluid Forces ◽  
Gap Flow ◽  
Base Bleed ◽  
Primary Frequency

An investigation on the flow around three side-by-side square prisms can provide a better understanding of complicated flow physics associated with multiple, closely spaced structures in which more than one gap flow is involved. In this paper, the flow around three side-by-side square prisms at a Reynolds number $Re=150$ is studied systematically at $L/W=1.1{-}9.0$, where $L$ is the prism centre-to-centre spacing and $W$ is the prism width. Five distinct flow structures and their ranges are identified, viz. base-bleed flow ($L/W<1.4$), flip-flopping flow $(1.4<L/W<2.1)$, symmetrically biased beat flow $(2.1<L/W<2.6)$, non-biased beat flow $(2.6<L/W<7.25)$ and weak interaction flow $(7.25<L/W<9.0)$. Physical aspects of each flow regime, such as vortex structures, vortex dynamics, gap-flow behaviours, shedding frequencies and fluid forces, are discussed in detail. A secondary (beat) frequency other than the Strouhal frequency (primary frequency) is observed in the symmetrically biased and non-biased beat flows, associated with the beat-like modulation in $C_{L}$-peak or amplitude, where $C_{L}$ is the lift force coefficient. Here we reveal the generic and intrinsic origin of the secondary frequency, establishing its connections with the phase lag between the two shear-layer sheddings from the two sides of a gap. When the two sheddings are in phase, no viscous force acts at the interface (i.e. at the centreline of the gap) of the two sheddings, resulting in the largest fluctuations in streamwise momentum, streamwise velocity and pressure; the maximum $C_{L}$ amplitude thus features the in-phase shedding. Conversely, when the two sheddings are antiphase, a viscous force exists at the interface of the two sheddings and restricts the momentum fluctuation through the gap, yielding a minimum $C_{L}$ amplitude. When the phase relationship between the two sheddings changes from in phase to antiphase, the extra viscous force acting at the interface becomes larger and causes the $C_{L}$ amplitude to change from a maximum to a minimum.

Surface Roughness Effects on Circular Cylinders at High Reynolds Numbers

2002 ◽  
Author(s):  
M. Eaddy ◽  
W. H. Melbourne ◽  
J. Sheridan
Keyword(s):  
Surface Roughness ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Flow Induced Vibration ◽  
Roughness Effects ◽  
Vortex Induced Vibration ◽  
Smooth Cylinder ◽  
Lift Forces ◽  
High Reynolds ◽  
Effect Of Surface

The problem of flow-induced vibration has been studied extensively. However, much of this research has focused on the smooth cylinder to gain an understanding of the mechanisms that cause vortex-induced vibration. In this paper results of an investigation of the effect of surface roughness on the cross-wind forces are presented. Measurements of the sectional RMS fluctuating lift forces and the axial correlation of the pressures for Reynolds numbers from 1 × 105 to 1.4 × 106 are given. It was found that surface roughness significantly increased the axial correlation of the pressures to similar values found at high subcritical Reynolds numbers. There was little effect of the surface roughness on the sectional lift forces. The improved correlation of the vortex shedding means rough cylinders will be subject to larger cross-wind forces and an increased possibility of vortex-induced vibration compared to smooth cylinders.

scholarly journals The Effect of Boattail Angles on the Near-Wake Structure of Axisymmetric Afterbody Models at Low-Speed Condition

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
The Hung Tran
Keyword(s):  
Strouhal Number ◽  
Reynolds Shear Stress ◽  
Flow Behavior ◽  
Flow Characteristics ◽  
Wake Flow ◽  
Turbulent Intensity ◽  
Near Wake ◽  
Wake Structure ◽  
Low Speed ◽  
Speed Condition

The effect of a boattail angle on the structure of the wake of an axisymmetric model was investigated at low-speed condition. Four conical boattail models with angles of 0° (blunt-based body), 10°, 16°, and 22° were selected for this study. The Reynolds number based on the diameter of the model was around 1.97×104. Particle image velocimetry (PIV) was used to measure the velocity of the wake flow. The time-averaged flow characteristics including the length of recirculation of the afterbody, turbulent intensity, and Reynolds shear stress were analyzed and compared among those boattail models. The experimental results showed that the length of recirculation decreases with increasing boattail angle to 16°. At a boattail angle above 16°, the flow was fully separated near the shoulder and near-wake structure was highly changed. The turbulent intensity at a boattail angle of 22° showed a similar level to that in the case of the blunt-based body. Flow behavior on boattail surface should be accounted as an important parameter affecting the wake width and drag of the model. Power spectral density and proper orthogonal decomposition (POD) analyses showed that a Strouhal number of StD=0.2 dominated for the boattail model up to 16°. The fully separated flow was dominated by a Strouhal number of StD=0.03−0.06, which was firstly presented in this study.

Experimental Study on Flow-Induced Vibration of Floating Squared Section Cylinders With Low Aspect Ratio: Part I — Effects of Incidence Angle

2015 ◽  
Author(s):  
Rodolfo T. Gonçalves ◽  
Dênnis M. Gambarine ◽  
Felipe P. Figueiredo ◽  
Fábio V. Amorim ◽  
André L. C. Fujarra
Keyword(s):  
Aspect Ratio ◽  
Incidence Angle ◽  
Ocean Basin ◽  
Circular Cylinders ◽  
Structural Damping ◽  
Flow Induced Vibration ◽  
Double Frequency ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Elastically Supported

Experiments regarding flow-induced vibration on floating squared section cylinders with low aspect ratio were carried out in an ocean basin with rotating-arm apparatus. The floating squared section cylinders were elastically supported by a set of linear springs to provide low structural damping to the system. Three different aspect ratios were tested, namely L/D = 1.0, 2.0 and 3.0, and two different incidence angles, namely 0 and 45 degrees. The aims were to understanding the flow-induced vibration around single columns of multi-column platforms, such as semi-submersible and TLP. VIV on circular cylinders were also carried out to compare the results. The range of Reynolds number covered was 2,000 < Re < 27,000. The in-line and transverse amplitude results showed to be higher for 45-degree incidence compared with 0-degree, but the maximum amplitudes for squared section cylinders were lower compared with the circular ones. The double frequency in the in-line motion was not verified as in circular cylinders. The yaw amplitudes cannot be neglected for squared section cylinders, maximum yaw amplitudes around 10 degrees were observed for reduced velocities up to 15.

Fluidelastic Instability of an Infinite Double Row of Circular Cylinders Subject to a Uniform Cross-Flow

1983 ◽  
Vol 105 (1) ◽  
pp. 59-66 ◽  
Author(s):  
S. J. Price ◽  
M. P. Paidoussis
Keyword(s):  
Aerodynamic Force ◽  
Mass Parameter ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Frequency Detuning ◽  
Complex Flow ◽  
Force Coefficient ◽  
Double Row ◽  
Mechanical Coupling ◽  
Fluid Damping

This paper represents the first stage of a fundamental investigation of the vibration phenomena induced in heat exchanger bundles subject to a cross-flow. Using aerodynamic force coefficient data, obtained experimentally from a static wind tunnel model, a linearized quasi-static analysis is employed to analyze the stability of an infinite double row of circular cylinders in uniform cross-flow. From the analysis it is shown that the instability is a result of the negative fluid damping forces, resulting from the complex flow pattern in the row. A new expression is obtained relating the critical velocity for the onset of instability to the damping parameter, the mass parameter and the pitch ratio of the cylinders. The expression is compared with experimental data available in the literature, from dynamic laboratory results, and a good correlation is obtained. Using this stability analysis the effect of mechanical coupling and frequency detuning, both between modes in one cylinder and modes in adjacent cylinders, is examined. In general it is shown that mechanical coupling is destabilizing and frequency detuning stabilizing.

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