Tag Archives: Vertical axis

Simulations of a vertical axis turbine in a channel


Anders Goude and Olov Ågren – Renewable Energy, March 2014

Abstract

The power coefficient of a turbine increases according to the predictions from streamtube theory for sites with a confined fluid flow. Here, a vertical axis turbine (optimized for free flow) has been simulated by a two-dimensional vortex method, both in a channel and in free flow. The first part of the study concerns the numerical parameters of channel simulations. It is found that for free flow and wide channels, a large number of revolutions is required for convergence (around 100 at the optimal tip speed ratio and increasing with higher tip speed ratio), while for smaller channels, the required number of revolutions decreases. Continue reading

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Numerical Simulation of a Straight-Bladed Vertical-Axis Water Turbine Operating in a 2 m/s Current


Marco Raciti Castelli and Ernesto Benini – Applied Mechanics and Materials, June 2013

Abstract

The present work proposes a full campaign of simulation of a Darrieus-type Vertical-Axis Water Turbine (VAWaterT) operating in an open flow-field. After describing the computational model and the relative validation procedure, a complete campaign of simulations based on full RANS unsteady calculations is presented for a three-bladed rotor architecture, characterized by a NACA 0025 blade profile. Flow field characteristics are investigated for several values of tip speed ratio and for a constant unperturbed free-stream water velocity of 2 m/s. Finally, the torque coefficient generated from the three blades is determined for each simulated angular velocity, allowing the calculation of the rotor power-curve. Keywords: Vertical-Axis Water Turbine, hydrokinetic technology, CFD, NACA 0025.

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Hydro-Kinetic Energy Conversion: Resource and Technology


M. Grabbe – PhD Dissertation, Uppsala University, April, 2013

Abstract

The kinetic energy present in tidal currents and other water courses has long been appreciated as a vast resource of renewable energy. The work presented in this doctoral thesis is devoted to both the characteristics of the hydro-kinetic resource and the technology for energy conversion. An assessment of the tidal energy resource in Norwegian waters has been carried out based on available data in pilot books. More than 100 sites have been identified as interesting with a total estimated theoretical resource—i.e. the kinetic energy in the undisturbed flow—in the range of 17 TWh. A second study was performed to analyse the velocity distributions presented by tidal currents, regulated rivers and unregulated rivers. The focus is on the possible degree of utilization (or capacity factor), the fraction of converted energy and the ratio of maximum to rated velocity, all of which are believed to be important characteristics of the resource affecting the economic viability of a hydro-kinetic energy converter.

The concept for hydro-kinetic energy conversion studied in this thesis comprises a vertical axis turbine coupled to a directly driven permanent magnet generator. One such cable wound laboratory generator has been constructed and an experimental setup for deployment in the river Dalälven has been finalized as part of this thesis work. It has been shown, through simulations and experiments, that the generator design at hand can meet the system requirements in the expected range of operation. Experience from winding the prototype generators suggests that improvements of the stator slot geometry can be implemented and, according to simulations, decrease the stator weight by 11% and decrease the load angle by 17%. The decrease in load angle opens the possibility to reduce the amount of permanent magnetic material in the design.

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Blockage effects on the hydrodynamic performance of a marine cross-flow turbine


C. Consul, R. Willden and S. McIntosh – Phil. Trans. R. Soc. A, 2013

Abstract

This paper explores the influence of blockage and free-surface deformation on the hydrodynamic performance of a generic marine cross-flow turbine. Flows through a three-bladed turbine with solidity 0.125 are simulated at field-test blade Reynolds numbers, O(105–106), for three different cross-stream blockages: 12.5, 25 and 50 per cent. Two representations of the free-surface boundary are considered: rigid lid and deformable free surface. Increasing the blockage is observed to lead to substantial increases in the power coefficient; the highest power coefficient computed is 1.23. Only small differences are observed between the two free-surface representations, with the deforming free-surface turbine out-performing the rigid lid turbine by 6.7 per cent in power at the highest blockage considered. This difference is attributed to the increase in effective blockage owing to the deformation of the free surface. Hydrodynamic efficiency, the ratio of useful power generated to overall power removed from the flow, is found to increase with blockage, which is consistent with the presence of a higher flow velocity through the core of the turbine at higher blockage ratios. Froude number is found to have little effect on thrust and power coefficients, but significant influence on surface elevation drop across the turbine.

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The Hydrodynamic Characteristics of a Free Variable-pitch Vertical Axis Tidal Turbine


X-W. Zhang, S-Q. Wang, F. Wang, L. Zhang, and O-H. Sheng – Journal of Hydrodynamics, Series B, December, 2012

Abstract

The hydrodynamic characteristics of a free variable-pitch vertical axis tidal turbine are investigated by combining experimental and numerical simulations. The variations of hydrodynamics are obtained based on testing the kinematics and the dynamics of the turbine under different flow and structural conditions. Through analyzing the movement of the turbine and the characteristics of the flow field by numerical simulations, it is shown how the turbine’s performance is improved.

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Flow control for VATT by fixed and oscillating flap


Q. Xiao, W. Liu, and A. Incecik – Renewable Energy, March, 2013

Abstract

The present study is aimed to explore the potential to improve Vertical Axis Tidal Turbine (VATT) energy harnessing efficiency by using modified blades with fixed and oscillating flap. The fixed flap concept is borrowed from its application in aerodynamics area for reaching a high lift force at low flying speed. Oscillating flap is motivated by our relevant biomimetic studies on the flapping wing propulsion or energy extraction. Present investigation is concentrated on a VATT with NACA 0018 profile blade as its baseline turbine. Numerical simulations are carried out by solving incompressible Unsteady Navier–Stokes equations at turbulence flow condition. Computed results show that under certain optimal flap geometry and flow conditions, turbine power coefficient reaches 28% enhancement as compared to the conventional blade turbine. Detailed analysis on the flow structure demonstrates that this is related to the effective flow separation suppression and vortex control by applying a fixed and oscillating flap.

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System Perspectives on Hydro-Kinetic Energy Conversion


K. Yuen – Uppsala University, 2012

Abstract

Free-flowing water currents such as tides and unregulated water courses could contribute to world electricity production given the emergence of robust technical solutions for extracting the energy. At Uppsala University, a concept for converting the energy in water currents to electricity using a vertical axis turbine with fixed blade-pitch and a direct-drive permanent magnet generator is studied. Continue reading

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