Experimental characterisation of the wake behind paired vertical-axis wind turbines (original) (raw)
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Wind tunnel experiments of a pair of interacting vertical-axis wind turbines
Journal of Physics: Conference Series, 2018
Vertical-axis wind turbines (VAWTs) have received a renewed interest in the wind energy research community, mainly for offshore applications. One advantage is that installing a pair of counterrotating VAWTs on the same floating platform would result in thrust reduction and potential cancellation of the mooring yaw moment. In addition, such configurations could benefit from increased power output and reduced wake losses. In this article, we report on wind tunnel experiments to study the mechanical power output of a reference VAWT scale model, tested individually and in a closely-spaced pair of VAWTs. The power output of the individual VAWT configuration is compared with a pair of VAWTs spaced 1.3 diameters apart for two counterrotating directions. A net power increase in the power coefficient for the paired configuration of up to 17.0 % compared with two individual rotors has been observed.
Adjacent Wake Effect of a Vertical Axis Wind Turbine
Procedia Engineering, 2015
The main objective of this study is to understand the effect of turbine placement and surrounding structures. Using Urban Green Energy's UGE-4K vertical axis wind turbine and the ANSYS computational fluid dynamics package (CFX), a dynamic fluid analysis was undertaken looking at the wake of the turbine through a variety of different inlet speeds and rotational frequencies to determine suitable flow recovery for optimal placement of subsequent turbines. The results showed that the wake interference is minimal at around 5 times the diameter of the turbine downstream. Results also show that flow recovery was a lot slower to the right of the turbine especially along a line 15° from the centre of the turbine to the right as this is coincident with the vortices generated from the turbines rotation.
Simulation and wake analysis of a single vertical axis wind turbine
Wind Energy, 2016
Because of several design advantages and operational characteristics, particularly in offshore farms, vertical axis wind turbines (VAWTs) are being reconsidered as a complementary technology to horizontal axial turbines. However, considerable gaps remain in our understanding of VAWT performance since cross-flow rotor configurations have been significantly less studied than axial turbines. This study examines the wakes of VAWTs and how their evolution is influenced by turbine design parameters. An actuator line model is implemented in an atmospheric boundary layer large eddy simulation code, with offline coupling to a high-resolution blade-scale unsteady Reynolds-averaged Navier-Stokes model. The large eddy simulation captures the turbine-to-farm scale dynamics, while the unsteady Reynolds-averaged Navier-Stokes captures the blade-to-turbine scale flow. The simulation results are found to be in good agreement with three existing experimental datasets. Subsequently, a parametric study of the flow over an isolated VAWT, carried out by varying solidities, height-todiameter aspect ratios and tip speed ratios, is conducted. The analyses of the wake area and velocity and power deficits yield an improved understanding of the downstream evolution of VAWT wakes, which in turn enables a more informed selection of turbine designs for wind farms.
2015
The main objective of this study is to understand the effect of turbine placement and surrounding structures. Using Urban Green Energy’s UGE-4K vertical axis wind turbine and the ANSYS computational fluid dynamics package (CFX), a dynamic fluid analysis was undertaken looking at the wake of the turbine through a variety of different inlet speeds and rotational frequencies to determine suitable flow recovery for optimal placement of subsequent turbines. The results showed that the wake interference is minimal at around 5 times the diameter of the turbine downstream. Results also show that flow recovery was a lot slower to the right of the turbine especially along a line 15° from the centre of the turbine to the right as this is coincident with the vortices generated from the turbines rotation. © 2015 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of organizing committee of the 6th BSME International Conference on Thermal Engineering (ICTE 2014).
Experimental Investigation of Wind Turbine Wakes in the Wind Tunnel
Energy Procedia, 2013
Detailed wake measurements of two model wind turbine setups in the wind tunnel were performed. Two similar model wind turbines with a rotor diameter of 0.9m were operated in the large closed--loop wind tunnel of the Department of Energy and Process Engineering at The Norwegian University of Science and Technology. A single turbine arrangement and a tandem setup, where a wind turbine was operated in the wake of an upstream turbine wind turbine, were tested. Measurements of the cross section in the near and far wake as well as measurements in axial direction are presented. The wake measurements mainly agree with wakes predicted by wake theory. However, a strong tower wake was observed. The influence of the tower is often not covered by wake theory and computational models. The tower wake deflected as it interacted with the rotating rotor wake. A strongly non--uniform velocity and turbulence distribution in the far wake was found. A relationship to the influence of the tower wake is expected.
Wind turbine wake interactions; results from blind tests
Journal of Physics: Conference Series, 2015
Results from three "Blind test" Workshops on wind turbine wake modeling are presented. While the first "Blind test" (BT1, 2011) consisted of a single model turbine located in a large wind tunnel, the complexity was increased for each new test in order to see how various models performed. Thus the next "Blind test" (BT2, 2012) had two turbines mounted in-line. This is a crucial test for models intended to predict turbine performances in a wind farm. In the last "Blind test" (BT3, 2013) the two turbines were again mounted in-line, but offset sideways so that the rotor of the downstream turbine only intersected half the wake from the upstream turbine. This case produces high dynamic loads and strong asymmetry in the wake. For each "Blind test" the turbine geometry and wind tunnel environment was specified and the participants were asked to predict the turbine performances, as well as the wake development to five diameters downstream of the second turbine. For the first two tests axisymmetry could be assumed if the influence of the towers was neglected. This was not possible in BT3 and therefore only fully 3D methods could be applied. In all tests the prediction scatter was surprisingly high.
An Experimental Investigation on the Wake Characteristics behind a Novel Twin-Rotor Wind Turbine
33rd Wind Energy Symposium, 2015
An experimental study was performed to examine the wake characteristics and aeromechanic performance of an innovative twin-rotor wind turbine (TRWT) in comparison with those of a conventional single-rotor wind turbine (SRWT). The comparative study was conducted in a large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) wind tunnel with the TRWT and SRWT model sited in simulated atmospheric boundary layer (ABL) winds under neutral stability conditions. In addition to measuring the power outputs of the TRWT and SRWT models, dynamic wind loads acting on the wind turbine models were also investigated in detail. Furthermore, a high-resolution PIV system was used for detailed wake flow field measurements (free-run and phase-locked) in order to quantify the characteristics of the turbulent turbine wake flows and to quantitatively visualize the transient behavior of the unsteady vortex structures behind the wind turbine models. The detailed flow field measurements are correlated with the dynamic wind loads and power output measurements to elucidate the underlying physics for higher total power generation and better durability of the wind turbines.
Experimental investigation of wake effects on wind turbine performance
Renewable Energy, 2011
The wake interference effect on the performance of a downstream wind turbine was investigated experimentally. Two similar model turbines with the same rotor diameter were used. The effects on the performance of the downstream turbine of the distance of separation between the turbines and the amount of power extracted from the upstream turbine were studied. The effects of these parameters on the total power output from the turbines were also estimated. The reduction in the maximum power coefficient of the downstream turbine is strongly dependent on the distance between the turbines and the operating condition of the upstream turbine. Depending on the distance of separation and blade pitch angle, the loss in power from the downstream turbine varies from about 20 to 46% compared to the power output from an unobstructed single turbine operating at its designed conditions. By operating the upstream turbine slightly outside this optimum setting or yawing the upstream turbine, the power output from the downstream turbine was significantly improved. This study shows that the total power output could be increased by installing an upstream turbine which extracts less power than the following turbines. By operating the upstream turbine in yawed condition, the gain in total power output from the two turbines could be increased by about 12%.
An Experimental Study of the Near Wake of Horizontal Axis Wind Turbines AIAA (2)
The present work considers an experimental investigation of wind turbine near wake by using Particle Image Velocimetry (PIV) visualization technique. The PIV technique gives a complete picture of all points at the domain under consideration. The study is focused on the effect of tip speed ratio () and Reynolds number (Rec) on the near wake characteristics.A three-blade model of wind turbine with airfoil SG 6040 16% is tested in water channel at Re c range between 1.28 ×10 4 and 7.68 ×10 4 . Various tip speed ratios are tested between =2 and =12. Experiments are also performed at constant =8 and variable Rec in the range between 2.56 ×10 4 and 5.12 ×10 4 .
Upstream and lateral wind turbine wake effects on nearby wind turbine performance
Journal of Wind Engineering and Industrial Aerodynamics, 1990
A selection of different 1:50 scale rotor blades were evaluated with dynamometers, force balances, and wake measurements to select a rotor model which correctly simulates the full-scale behavior of an actual wind mill. A wind-tunnel measurement program was then carried out on a set of five dynamic (operating) wind mills placed at various heights and orrientations to one another. The interdependence of wind-turbine performance on such spacing was determined.