scholarly journals Minimising turbine thrust variation in multi-rotor tidal fences

2020 ◽  
Vol 6 (3) ◽  
pp. 293-302
Author(s):  
T. F. L. Stephenson ◽  
C. R. Vogel
Keyword(s):  
Performance Enhancement ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Recent Analysis ◽  
Minimal Impact ◽  
Energy Devices ◽  
Tidal Turbines ◽  
Significant Performance ◽  
Tidal Stream ◽  
Tidal Stream Energy

Abstract Recent analysis of tidal stream energy devices has focussed on maximising power output. Studies have shown that significant performance enhancement can be achieved through the constructive interference effects that develop between tidal stream turbines by deploying them close together. However, this results in variation in the flow incident on the turbines and hence leads to thrust variation across the turbine fence. This may lead to varying damage rates across the fence with adverse impacts on operation and maintenance costs over the turbine lifetime. This study investigates strategies to reduce thrust variation across fences of tidal turbines using three-dimensional Reynolds-Averaged Navier–Stokes simulations. It is shown that the variation in turbine thrust across a fence of eight turbines can be reduced to within 1% with minimal impact on the fence power. Furthermore, by reducing the rotational speed of inboard turbines, or varying the blade pitch angle of the turbines across the fence, it is possible to reduce overall turbine loads and increase the power to thrust ratio of the turbines.

scholarly journals Characterization of the vertical evolution of the three-dimensional turbulence for fatigue design of tidal turbines

2020 ◽  
Vol 378 (2178) ◽  
pp. 20190495 ◽  
Author(s):  
Maxime Thiébaut ◽  
Jean-François Filipot ◽  
Christophe Maisondieu ◽  
Guillaume Damblans ◽  
Christian Jochum ◽  
...  
Keyword(s):  
Turbulence Intensity ◽  
Large Scale ◽  
Three Dimensional ◽  
Vertical Direction ◽  
Tidal Energy ◽  
Tidal Turbines ◽  
Tidal Stream ◽  
Vertical Evolution ◽  
Tidal Stream Energy ◽  
Scale Turbulence

A system of two coupled four-beam acoustic Doppler current profilers was used to collect turbulence measurements over a 36-h period at a highly energetic tidal energy site in Alderney Race. This system enables the evaluation of the six components of the Reynolds stress tensor throughout a large proportion of the water column. The present study provides mean vertical profiles of the velocity, the turbulence intensity and the integral lengthscale along the streamwise, spanwise and vertical direction of the tidal current. Based on our results and considering a tidal-stream energy convertor (TEC) aligned with the current main direction, the main elements of turbulence prone to affect the structure (material fatigue) and to alter power generation would likely be: (i) the streamwise turbulence intensity ( I x ), (ii) the shear stress, v ′ w ′ ¯ , (iii) the normal stress, u ′ 2 ¯ and (iv) the vertical integral lengthscale ( L z ). The streamwise turbulence intensity, ( I x ), was found to be higher than that estimated at other tidal energy sites across the world for similar height above bottom. Along the vertical direction, the length ( L z ) of the large-scale turbulence eddies was found to be equivalent to the rotor diameter of the TEC Sabella D10. It is considered that the turbulence metrics presented in this paper will be valuable for TECs designers, helping them optimize their designs as well as improve loading prediction through the lifetime of the machines. This article is part of the theme issue ‘New insights on tidal dynamics and tidal energy harvesting in the Alderney Race’.

scholarly journals Unsteady flow around a two-dimensional section of a vertical axis turbine for tidal stream energy conversion

2009 ◽  
Vol 1 (2) ◽  
Author(s):  
Hyun Ju Jung ◽  
Ju Hyun Lee ◽  
Shin Hyung Rliee ◽  
Museok Song ◽  
Beom-Soo Hyun
Keyword(s):  
Unsteady Flow ◽  
Energy Conversion ◽  
Stokes Equations ◽  
Vertical Axis ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Navier Stokes Equations ◽  
Tidal Stream ◽  
Tidal Stream Energy ◽  
Vertical Axis Turbine

ABSTRACTThe two-dimensional unsteady flow around a vertical axis turbine for tidal stream energy' conversion was investigated using a computational fluid dynamics tool solving the Reynolds-Averaged Navier-Stokes equations. The geometry' of the turbine blade section was NACA653-01S airfoil. The computational analysis was done at several different angles of attack and the results were compared with the corresponding experimental data for validation and calibration. Simulations were then carried out for the two-dimensional cross section of a vertical axis turbine. The simulation results demonstrated the usefulness of the method for the typical unsteady flows around vertical axis turbines. The optimum turbine efficiency was achieved for carefully selected combinations of the number of blades and tip speed ratios.

On the Tidal Stream Resource of Two Headland Sites in the English Channel: Portland Bill and Isle of Wight

2014 ◽  
Author(s):  
Thomas A. A. Adcock ◽  
Scott Draper
Keyword(s):  
Field Measurements ◽  
Head Loss ◽  
English Channel ◽  
Mean Power ◽  
Isle Of Wight ◽  
Tidal Turbines ◽  
Actuator Disc ◽  
Tidal Stream ◽  
Tidal Stream Energy ◽  
The Mean

There are various candidate sites for tidal stream energy extraction in the English Channel. In this paper we examine the tidal stream resource at Portland Bill and the south coast of the Isle of Wight. A depth-averaged numerical model is developed and compared to field measurements. The presence of rows of tidal turbines is simulated using a line-discontinuity to represent the head loss across the turbines. The head loss is given by linear momentum actuator disc theory. At each site the length of the turbine rows, the local blockage ratio, and the location of the turbines are varied. For Portland Bill the presence of an array with multiple rows of turbines is also considered. We find that it is likely that (based purely on the hydrodynamics) power could viably be extracted at each site, with the mean power produced by each site being in the order of 10s MW.

Numerical Investigation of an Optimised Horizontal Axis Tidal Stream Turbine

2019 ◽  
Author(s):  
Hassan El Sheshtawy ◽  
Ould el Moctar ◽  
Thomas E. Schellin ◽  
Satish Natarajan
Keyword(s):  
Output Power ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Speed Ratio ◽  
Navier Stokes Equations ◽  
Tidal Turbines ◽  
Tidal Turbine ◽  
Sst Turbulence Model ◽  
Tidal Stream ◽  
Tidal Stream Turbine

Abstract A tidal stream turbine was designed using one of the optimised hydrofoils, whose lift-to-drag ratio at an angle of attack of 5.2 degrees was 4.5% higher than that of the reference hydrofoil. The incompressible Reynolds-averaged Navier Stokes equations in steady state were solved using k-ω (SST) turbulence model for the reference and optimised tidal stream turbines. The discretisation errors and the effect of different y+ values on the solution were analysed. Thrust and power coefficients of the modelled reference turbine were validated against experimental measurements. Output power and thrust of the reference and the optimised tidal turbines were compared. For a tip speed ratio of 3.0, the output power of the optimised tidal turbine was 8.27% higher than that of the reference turbine of the same thrust.

scholarly journals Two-scale dynamics of flow past a partial cross-stream array of tidal turbines

2013 ◽  
Vol 730 ◽  
pp. 220-244 ◽  
Author(s):  
Takafumi Nishino ◽  
Richard H. J. Willden
Keyword(s):  
Analytical Model ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Wake Region ◽  
Near Wake ◽  
New Model ◽  
Tidal Turbines ◽  
Type Design ◽  
Flow Past ◽  
Far Wake

AbstractThe characteristics of flow past a partial cross-stream array of (idealized) tidal turbines are investigated both analytically and computationally to understand the mechanisms that determine the limiting performance of partial tidal fences. A two-scale analytical partial tidal fence model reported earlier is further extended by better accounting for the effect of array-scale flow expansion on device-scale dynamics, so that the new model is applicable to short fences (consisting of a small number of devices) as well as to long fences. The new model explains theoretically general trends of the limiting performance of partial tidal fences. The new model is then compared to three-dimensional Reynolds-averaged Navier–Stokes (RANS) computations of flow past an array of various numbers (up to 40) of actuator disks. On the whole, the analytical model agrees well with the RANS computations, suggesting that the two-scale dynamics described in the analytical model predominantly determines the fence performance in the RANS computations as well. The comparison also suggests that the limiting performance of short partial fences depends on how much of device far-wake mixing takes place within the array near-wake region. This factor, however, depends on the structures of the wake and therefore on the type/design of devices to be arrayed.

Investigation of Three Dimensional Tidal Stream Energy in Surrounding Water Areas of ZTD, China

2013 ◽  
Vol 774-776 ◽  
pp. 262-266
Author(s):  
Bing Chen Liang ◽  
Tao Tao Zhang ◽  
Hong Da Shi
Keyword(s):  
Numerical Modeling ◽  
Energy Density ◽  
Tidal Current ◽  
Current Model ◽  
Three Dimensional ◽  
Coastal Zones ◽  
Surrounding Water ◽  
Tidal Current Velocity ◽  
Tidal Stream ◽  
Tidal Stream Energy

In the present work, the tidal stream energy in surrounding coastal zones of ZTD is calculated. The tidal current velocity is gotten by three dimensional numerical modeling. The tidal current model is validated by measurement of tidal current observed in 4 points surrounding ZTD. The numerical results given by the tidal current model already shows that: the tidal current velocities given by the model agree with the measured velocities generally. The characteristics of tidal currents around ZTD are analyzed and the following tidal stream energy density is calculated. The maximum tidal stream energy flux of unit width occurs around the middle locations of ZTD southern areas.

scholarly journals Tidal stream energy site assessment via three-dimensional model and measurements

2013 ◽  
Vol 102 ◽  
pp. 510-519 ◽  
Author(s):  
Paul A. Work ◽  
Kevin A. Haas ◽  
Zafer Defne ◽  
Thomas Gay
Keyword(s):  
Three Dimensional ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Site Assessment ◽  
Tidal Stream ◽  
Tidal Stream Energy

A Numerical Analysis of Bidirectional Ducted Tidal Turbines in Yawed Flow

2013 ◽  
Vol 47 (4) ◽  
pp. 23-35 ◽  
Author(s):  
Clarissa S.K. Belloni ◽  
Richard H.J. Willden ◽  
Guy T. Houlsby
Keyword(s):  
Computational Study ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Navier Stokes ◽  
External Diameter ◽  
Tidal Turbines ◽  
Turbine Performance ◽  
Ducted Turbine ◽  
Flow Through ◽  
Porous Disc

AbstractThe paper presents a computational study of ducted bidirectional tidal turbines using three-dimensional Reynolds-averaged Navier-Stokes simulations. We model the outer duct as a solid body and use a porous disc to represent the turbine rotor, a simplification that captures changes in linear momentum and thus the primary interaction of the turbine with the flow through and around the duct while greatly reducing computational complexity. The duct is modeled using linearly converging and diverging sections and a short straight pipe at the duct throat.We investigate the performance of bare and ducted turbines and relate these to the flows through the devices. For the ducted turbine under investigation, we show a substantial decrease in power generated relative to a bare turbine of diameter equal to the external diameter of the duct. In the case of ducted turbines with concave duct exteriors, we observe two external flow regimes with increasing turbine thrust: nozzle-contoured and separation dominated regimes. Maximum power occurs within the separation dominated flow regime due to the additional channel blockage created by the external separation.The ducts of ducted tidal turbines have been argued to provide a flow straightening effect, allowing modest yaw angles to be readily accommodated. We present a comparison of bare and ducted turbine performance in yawed flow. We show that while bare turbine performance decreases in yawed flow, ducted turbine performance increases. This is due to both a flow straightening effect and also an increase in effective blockage as ducts present greater projected frontal area when approached nonaxially.

Experimental and Theoretical Studies for Improving the Performance of a Modified Shape Savonius Wind Turbine

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
W. A. El-Askary ◽  
Ahmed S. Saad ◽  
Ali M. AbdelSalam ◽  
I. M. Sakr
Keyword(s):  
Wind Velocity ◽  
Turbulence Model ◽  
Three Dimensional ◽  
Power Coefficient ◽  
Navier Stokes ◽  
Optimized Design ◽  
Percentage Increase ◽  
Aspect Ratios ◽  
Air Jet ◽  
Significant Performance

Abstract In this paper, measurements and computations are performed to study the performance of a 45-deg twisted Savonius rotor with a modified profile, at various overlap ratios (δ), aspect ratios (AR), and wind velocity (V). A free air jet test rig is used to carry out the experiments, while three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) equations are used, in conjunction with the renormalization group (RNG) k–ɛ turbulence model, to perform the computations. The present experimental results successfully verify the simulation predictions obtained by the selected turbulence model. The RNG k–ɛ turbulence model has been chosen based on previous tests performed and published by the authors. Furthermore, both torque coefficient (CT) and power coefficient (CP) are numerically predicted at various tip speed ratios (λ) for overlap ratios (δ) ranging from 0.0 to 0.5, aspect ratios (AR) ranging from 0.75 to 3, and wind velocity values ranging from 4 to 18 m/s. Unlike the conventional rotor, the present twisted rotor with a modified profile produces significant performance improvement in the case of modified rotor without overlapping (δ = 0.0). Moreover, the peaks of CT and CP of the twisted rotor with the modified profile are enhanced with the increase in the aspect ratio. However, the percentage increase is noticed to be insignificant for AR greater than two. The maximum power coefficient (CPmax) for the twisted rotor with the modified profile and optimized design is 0.305 at a wind velocity of 6 m/s, with a performance gain of 75.3% compared to the conventional Savonius wind rotor which has CPmax=0.174.

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