Envelope of Power Harvested by a Single-Cylinder VIVACE Converter

2015 ◽  
Author(s):  
Jianhui Liu ◽  
Michael M. Bernitsas
Keyword(s):  
Damping Ratio ◽  
Reynolds Numbers ◽  
High Amplitude ◽  
Navier Stokes ◽  
Number Range ◽  
Turbulence Control ◽  
Single Cylinder ◽  
Hydrokinetic Energy ◽  
Grid Interface ◽  
Vortex Induced Vibrations

Flow Induced Motions (FIM) of a single-cylinder VIVACE Converter is investigated using two-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with the Spalart-Allmaras turbulence model at Reynolds numbers (30,000 ≤Re≤120,000, 5.50≤U*≤9.85) in the TrSL3 flow regime. Computational results compare very well with experimental data. With implementation of Passive Turbulence Control (PTC), the VIVACE Converter can harness hydrokinetic energy from currents or tides over an expanded range of FIM synchronization, including Vortex Induced Vibrations (VIV) and galloping. The General Grid Interface (GGI) with topological mesh changes is proved to be an effective method for handling high-amplitude FIM response. Within the test Reynolds number range, five regions are clearly observed, including the no-FIM range, the VIV initial branch, the VIV upper branch, transition from VIV to galloping, and galloping. The power envelope calculated based on the CDF simulations for FIM agrees very well with the corresponding power envelope generated based on experiments. The range between VIV and galloping can be eliminated by adjusting the spring-stiffness and the harnessing damping-ratio. This is verified by both experiments and numerical simulation.

Unsteady flow past a rotating circular cylinder at Reynolds numbers 103 and 104

1990 ◽  
Vol 220 ◽  
pp. 459-484 ◽  
Author(s):  
H. M. Badr ◽  
M. Coutanceau ◽  
S. C. R. Dennis ◽  
C. Ménard
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Unsteady Flow ◽  
Rotation Rate ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Number Range ◽  
Flow Past

The unsteady flow past a circular cylinder which starts translating and rotating impulsively from rest in a viscous fluid is investigated both theoretically and experimentally in the Reynolds number range 103 [les ] R [les ] 104 and for rotational to translational surface speed ratios between 0.5 and 3. The theoretical study is based on numerical solutions of the two-dimensional unsteady Navier–Stokes equations while the experimental investigation is based on visualization of the flow using very fine suspended particles. The object of the study is to examine the effect of increase of rotation on the flow structure. There is excellent agreement between the numerical and experimental results for all speed ratios considered, except in the case of the highest rotation rate. Here three-dimensional effects become more pronounced in the experiments and the laminar flow breaks down, while the calculated flow starts to approach a steady state. For lower rotation rates a periodic structure of vortex evolution and shedding develops in the calculations which is repeated exactly as time advances. Another feature of the calculations is the discrepancy in the lift and drag forces at high Reynolds numbers resulting from solving the boundary-layer limit of the equations of motion rather than the full Navier–Stokes equations. Typical results are given for selected values of the Reynolds number and rotation rate.

scholarly journals An asymptotic expansion for the vortex-induced vibrations of a circular cylinder

2011 ◽  
Vol 671 ◽  
pp. 137-167 ◽  
Author(s):  
PHILIPPE MELIGA ◽  
JEAN-MARC CHOMAZ
Keyword(s):  
Circular Cylinder ◽  
Stokes Equations ◽  
Structural Parameters ◽  
Coupled System ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Fluid Equation ◽  
Wake Oscillator ◽  
Vortex Induced Vibrations ◽  
Lower Magnitude

This paper investigates the vortex-induced vibrations (VIV) of a spring-mounted circular cylinder. We compute analytically the leading-order equations describing the nonlinear interaction of the fluid and structure modes by carrying out an asymptotic analysis of the Navier–Stokes equations close to the threshold of instability of the fluid-only system. We show that vortex-shedding can occur at subcritical Reynolds numbers as a result of the coupled system being linearly unstable to the structure mode. We also show that resonance occurs when the frequency of the nonlinear limit cycle matches the natural frequency of the cylinder, the displacement being then in phase with the flow-induced lift fluctuations. Using an extension of this model meant to encompass the effect of the low-order added-mass and damping forces induced by the displaced fluid, we show that the amount of energy that can be extracted from the flow can be optimized by an appropriate choice of the structural parameters. Finally, we suggest a possible connection between the present ‘exact’ model and the empirical wake oscillator model used to study VIV at high Reynolds numbers. We show that for the low Reynolds numbers considered here, the effect of the structure on the fluid can be represented by a first coupling term proportional to the cylinder acceleration in the fluid equation, and by a second term of lower magnitude, which can stem either from an integral term or from a term proportional to the third derivative of the cylinder position.

Two-dimensional simulations of vortex-induced vibration of a circular cylinder

2021 ◽  
pp. 147509022199097
Author(s):  
Asim Ozan Mutlu ◽  
Meral Bayraktar ◽  
Seyfettin Bayraktar
Keyword(s):  
Damping Ratio ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Vortex Induced Vibration ◽  
Disciplinary Problems ◽  
Smooth Cylinder ◽  
Type Flow ◽  
Low Mass ◽  
Drag And Lift

In the present study, one of the cross-disciplinary problems known as vortex-induced vibration is numerically investigated. Effects of four different low mass-damping ratios; ζ = 0.013, 0.028, 0.074, and 0.124 of a smooth cylinder are taken into account for transition of shear layer 2 (TrSL2) type flow that falls between the Reynolds numbers from 2500 to 10,830 utilizing a two-dimensional cylinder that is free to move in normal-direction. Unsteady Reynolds-Averaged Navier–Stokes solutions indicate that the general trend is well captured with the adopted shear stress transport k-ω turbulence model, however, due to two-dimensional limitations some results are not consistent with experimental data. An inverse relation between the mass-damping ratio and the transition from the upper to the lower branch is detected. Change of drag and lift coefficients with the reduced velocities revealed that the maximum drag coefficient increases with reduced velocity until it reaches Ur = 5 and then decreases dramatically while the lift coefficients decrease consistently from the beginning.

Effects of Axis Ratio on the Vortex-Induced Vibration and Energy Harvesting of Rhombus Cylinder

2014 ◽  
Author(s):  
Li Zhang ◽  
Heng Li ◽  
Lin Ding
Keyword(s):  
Wide Band ◽  
Reynolds Numbers ◽  
Mechanical Power ◽  
Navier Stokes ◽  
Axis Ratio ◽  
Vortex Induced Vibrations ◽  
Mechanical Power Output ◽  
Wake Patterns ◽  
Wake Modes ◽  
High Reynolds

The vortex-induced vibrations of a rhombus cylinder are investigated using two-dimensional unsteady Reynolds-Averaged Navier-Stokes simulations at high Reynolds numbers ranging from 10,000 to 120,000. The rhombus cylinder is constrained to oscillate in the transverse direction, which is perpendicular to the flow velocity direction. Three rhombus cylinders with different axis ratio (AR=0.5, 1.0, 1.5) are considered for comparison. The simulation results indicate that the vibration response and the wake modes are dependent on the axis ratio of the rhombus cylinder. The amplitude ratios are functions of the Reynolds numbers. And as the AR increases, higher peak amplitudes can be made over a significant wide band of Re. On the other hand, a narrow lock-in area is observed for AR=0.5 and AR=1.5 when 30,000<Re<50,000, but the frequency ratio of AR=1.0 monotonically increases at a nearly constant slope in the whole Re range. The vortex shedding mode is always 2S mode in the whole Re range for AR=0.5. However, the wake patterns become diverse with the increasing of Re for AR=1.0 and 1.5. In addition, the mechanical power output of each oscillating rhombus cylinder is calculated to evaluate the efficiency of energy transfer in this paper. The theoretical mechanical power P between water and a transversely oscillating cylinder is achieved. On the base of analysis and comparison, the rhombus cylinder with AR=1.0 is more suitable for harvesting energy from fluid.

scholarly journals Investigation of the steady and unsteady forces acting on a pair of circular cylinders in crossflow up to ultra-high Reynolds numbers

2021 ◽  
Vol 62 (8) ◽  
Author(s):  
Günter Schewe ◽  
Nils Paul van Hinsberg ◽  
Markus Jacobs
Keyword(s):  
Power Spectra ◽  
Low Frequency ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Supercritical Regime ◽  
Unsteady Forces ◽  
Number Range ◽  
Single Cylinder ◽  
High Reynolds Numbers ◽  
High Reynolds

AbstractMeasurements of the steady and unsteady forces acting on a pair of circular cylinders in crossflow are performed from subcritical up to ultra-high Reynolds numbers. The two cylinders with equal diameters d are arranged inline at two centre-to-centre distances: S/d = 2.8 and 4. The trend of the drag curve for the upstream cylinder $$Cd_{1}$$ C d 1 (Re) at both distances is similar to that for a single circular cylinder. The development of the drag curves $$Cd_{2}$$ C d 2 (Re, S/d = 2.8, 4) of the downstream cylinder is inverse to that of the upstream cylinder. For both cylinder spacing values, the drag on the downstream cylinder is negative for subcritical Reynolds numbers, increases abruptly to positive values at the beginning of the supercritical regime, and shows a significant dip at transcritical Reynolds numbers. This drag inversion indicates that the critical distance Sc decreases sharply in the supercritical Reynolds number range. For S/d = 2.8 at Re$$\rightarrow$$ → 10$$^{7}$$ 7 , the downstream cylinder experiences once more a thrust force. The curve of the Strouhal number St(Re) of the downstream cylinder for S/d = 4 is very close to that of a single cylinder. For Reynolds numbers of Re$$\approx$$ ≈ 1$$\times$$ × 10$$^{6}$$ 6 - 7$$\times$$ × 10$$^{6}$$ 6 , the Strouhal numbers have nearly equal values of St$$\approx$$ ≈ 0.22 - 0.24 for both distances. This is followed by a branching. For Re$$\rightarrow$$ → 10$$^{7}$$ 7 and the case S/d = 2.8, the Strouhal numbers dip at St = 0.17. However, for S/d = 4, they increase up to St = 0.27. In the supercritical range, two peaks occur in the power spectra for the large distance S/d = 4. Based on a wavelet analysis, we can conclude that the low-frequency mode, which does not occur for a single cylinder, is an interference effect. Graphic abstract

Modeling Vortex Shedding Over a Stationary Circular Cylinder

2006 ◽  
Author(s):  
Osama Marzouk ◽  
Ali H. Nayfeh ◽  
Imran Akhtar ◽  
Haider N. Arafat
Keyword(s):  
Circular Cylinder ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Offshore Structures ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Building Models ◽  
Vortex Induced Vibrations ◽  
The Time Domain ◽  
Lift And Drag

Numerical simulations of flow past a stationary circular cylinder at different Reynolds numbers have been performed using a computational fluid dynamics (CFD) solver that is based on the Reynolds-averaged Navier-Stokes equations (RANS). The results obtained are used to develop reduced-order models for the lift and drag coefficients. The models do not only match the numerical simulation results in the time domain, but also in the spectral domain. They capture the steady-state region with excellent accuracy. Further, the models are verified by comparing their results in the transient region with their counterparts from the CFD simulations and a very good agreement is found. The work performed here is a step towards building models for vortex-induced vibrations (VIV) encountered in offshore structures, such as risers and spars.

Numerical Study on the Effect of Tandem Spacing on Flow-Induced Motions of Two Cylinders With Passive Turbulence Control

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Lin Ding ◽  
Li Zhang ◽  
Chunmei Wu ◽  
Eun Soo Kim ◽  
Michael M. Bernitsas
Keyword(s):  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Circular Cylinders ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Turbulence Control ◽  
Flow Regime Transition ◽  
Vortex Induced Vibrations ◽  
Passive Turbulence Control

The effect of tandem spacing on the flow-induced motions (FIM) of two circular cylinders with passive turbulence control is investigated using two-dimensional (2D) unsteady Reynolds-averaged Navier–Stokes equations with the Spalart–Allmaras turbulence model. Results are compared to experiments in the range of Reynolds number of 30,000 < Re < 100,000. The center-to-center spacing between the two cylinders is varied from 2 to 6 diameters. Simulation results predict well all the ranges of FIM including vortex-induced vibrations (VIV) and galloping and match well with experimental measurements. For the upstream cylinder, the amplitude and frequency responses are not considerably influenced by the downstream cylinder when the spacing is greater than 2D. For the downstream cylinder, a rising amplitude trend in the VIV upper-branch can be observed in all the cases as is typical of flows in the TrSL3 flow regime (transition in shear layer 3; 2 × 104 < Re < 3 × 105). The galloping branch merges with the VIV upper-branch for spacing greater than three-dimensional (3D). Vortex structures show significant variation in different flow regimes in accordance with experimental observations. High-resolution postprocessing shows that the interaction between the wakes of cylinders results in various types of FIM.

scholarly journals A Numerical Study of the Effect of Vortex-Induced Vibrations on a Circular Cylinder Mounted under Elastic Support

2020 ◽  
Author(s):  
Hugo Canilho ◽  
Cristina Fael ◽  
José Páscoa
Keyword(s):  
Numerical Study ◽  
Practical Interest ◽  
Maximum Amplitude ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Low Reynolds Numbers ◽  
Vortex Induced Vibrations ◽  
Sst Turbulence Model ◽  
Lift And Drag ◽  
Good Agreement

Vortex Induced Vibration (VIV) of structures is of practical interest to many fields of engineering. The particular case of a rigid cylinder mounted under elastic supports and constrained to oscillate in a single direction is modelled using OpenFOAM’s two-dimensional Reynolds-averaged Navier-Stokes (RANS) equations with k-ω SST turbulence model. The model aimed for relativelly low Reynolds numbers (2500 ≤ Re ≤ 15000) and the results were compared with Khalak and Williamson’s experimental results with the intent of also evaluating maximum amplitude to diameter ratio, A/D, achieving good agreement between both computational and experimental data. Lift and drag coefficients, C

Modeling of a Hydrokinetic Energy Converter With Two Tandem Cylinders in Flow-Induced Oscillations

2020 ◽  
Author(s):  
Yanfang Lv ◽  
Michael M. Bernitsas ◽  
Sun Hai
Keyword(s):  
Bp Neural Network ◽  
Power Efficiency ◽  
Present Model ◽  
Damping Ratio ◽  
Bp Network ◽  
Power Harvesting ◽  
Hydrokinetic Energy ◽  
Tandem Cylinders ◽  
Vortex Induced Vibrations ◽  
Mass Spring

Abstract Flow Induced Oscillations (FIO) of tandem cylinders can be enhanced to harness hydrokinetic energy by varying the system parameters. In general, the Converter consists of two mass–spring–damper oscillators subjected to transverse FIOs and specifically Vortex Induced Vibrations and galloping. These FIOs are strongly influenced by variations of the inflow velocity, damping, stiffness, mass and in-flow center-to-center spacing L between two tandem cylinders. In turn, those influence the harnessed power and efficiency of the Converter. In previous experiments, the interactions between the cylinders were proven to be beneficial for the synergy of the cylinders. In this paper, modeling of tandem-cylinder converters is studied considering the Converter parameters, aiming at enhancing the cylinder synergy resulting in increased harnessed power by using a backpropagation (BP) neural network. The main conclusions are: (1) The surrogate model is constructed by a BP network using the experimental data to reduce excessive experimentation or computational inaccuracy. The harnessed power at different flow velocities is computed by the present model and is found to be consistent with experimental results not included in the modeling. (2) Increasing the damping ratio (0.20–0.30) of two tandem cylinders is conducive to improve the power efficiency, but has little effect on power harvesting. (3) In galloping, the harnessed power and its corresponding efficiency for the case of L/D = 1.57 perform at a higher level than that of bigger spacing ratios.

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