Wake Effect and Power Production of Wind Turbine Arrays (original) (raw)

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%.

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.

IJERT-Optimization of Wake Effect Performance in a Downstream Turbine by using Wind Tunnel Test

International Journal of Engineering Research and Technology (IJERT), 2019

https://www.ijert.org/optimization-of-wake-effect-performance-in-a-downstream-turbine-by-using-wind-tunnel-test https://www.ijert.org/research/optimization-of-wake-effect-performance-in-a-downstream-turbine-by-using-wind-tunnel-test-IJERTCONV7IS11001.pdf In this project we have discussed about the optimization of wake effect and then characteristics of the three blade horizontal axis of wind turbine and performance of downstream turbine by wind tunnel test. This project also involves the single turbine model for the flow characteristic performance of parameters like velocity, turbulence intensities and correlation in a wake flow effect. The performance of the upstream turbine of the blades flow of a small pitch angle provides a disturbance to create a blade turned faster, and drastic change in the velocity of blade and then turbulence occurred in wake in the wind turbine. Then gradually decrease the wake velocity of turbine swept area on the free stream. This also describes the performance of the stream wise velocity and tangential velocity in a blade swept area.

Effect of the wake behind wind rotor on optimum energy output of wind farms

Renewable Energy, 2013

This study deals with the modeling of the wake effect on the energy extracted from the wind farms. It covers the wake effect of the interaction of the upstream wind rotor with/without the upstream right and/or upstream left wind rotor. A mathematical model representing a single wake model based on the linear description of the wake is developed in order to predict the wind speed inside the wake region at any downstream distance within the wind farm. Two different types of turbines with diameters of 62 m and 100 m are considered. Accordingly the effect of the wake on the energy produced from the wind farms is estimated. A number of different wind farm layouts are studied. Case studies including 3  3, 4  4, 6  6, 1  16, 16  1, 2  8, and 8  2 layouts are considered. Extracted energy is calculated in each case and an optimum layout is determined from different layouts. The effectiveness of the other layouts with respect to the optimum is obtained. The results showed that there is a drop in the annual extracted energy from the above mentioned layouts depending on the W.T. distances separating the W.T.'s. The wind speed was assumed to be 15 m/s with 10D downstream distances. The losses are estimated to be 20% for 3  3 (rows  column), 32% for 4  4, 46% for 6  6, 12.8% for 16  1, 23.3% for 2  8, and 29% for 8  2 when these layouts are compared to 1  16 layout as an optimum layout.

Assessment of blockage effects on the wake characteristics and power of wind turbines

Renewable Energy (2016)

Large Eddy Simulations (LES) are performed in order to study the wake and power characteristics of a horizontal-axis wind turbine in a wind tunnel. Using an actuator line technique, the effect of wind tunnel blockage ratio (defined as the ratio of the rotor swept area to the tunnel cross-sectional area) is investigated for a wide range of tip speed ratios from 1 to 12, and for four blockage ratios (0.2, 0.09, 0.05 and 0.02). The results demonstrate how the blockage effect increases with the tip speed ratio. When the tip speed ratio is close to or above the optimal design value, blockage ratios of larger than 0.05 affect both tangential and normal forces on the blades and therefore on the power and thrust coefficients. At the highest blockage ratio of 0.2, the mean velocity of the wake is also affected significantly, although the effect on the wake mixing rate is less pronounced. Further, the effect of the Reynolds number on the wake development is illustrated and the impact of numerics and subgrid-scale models are investigated by comparing two different LES codes. Finally, the importance of tip loss correction in actuator-line modeling of wind turbines is illustrated using comparative computations.

Influence of wind farm area dimension on wake and power production

At present, wind energy industry is facing major design constraints in boosting the power output. These can be overcome by setting up the right turbine at the right place. This paper proposes an optimized layout design of a wind farm by using Definite Point selection(DPS) and genetic algorithm, which can minimize the cost per unit power and minimum wake effects, while sustaining the obligatory space between adjacent turbines for operation safety. The existing cost per unit power can be reduced by changing the dimensions of wind farm with constant area. In this study, the velocity deficits caused by the wakes of each turbine were calculated by using Jensens wake model. The total area of wind farm 2 Km × 2 Km was divided into 10×10 cells with each cell having dimensions 200 m × 200 m. The results showed that power output of the wind farm by using the same area in different dimension was increased even when the total numbers of wind turbines were the same. It was observed that 32 wind ...

Large eddy simulation of the wind turbine wake characteristics in the numerical wind tunnel model

Journal of Wind Engineering and Industrial Aerodynamics, 2013

Large Eddy Simulation of NREL Phase VI wind turbine was performed in a virtual wind tunnel (24.4m by 36.6m) in order to achieve a better understanding of the turbine wake characteristics. For this purpose, ANSYS-Fluent package was used to run the simulation using the dynamic Smagorinsky-Lilly model. For the purpose of validation, the pressure distribution at different span-wise sections along the turbine blade and the power produced by the wind turbine were compared with the published experimental results for the NREL phase VI rotor tested in the NASA wind tunnel with the same dimensions as in the model and a good agreement was found between the two. The airflow immediately behind the wind turbine was observed to be a system of intense and stable rotating helical vortices, which determined the dynamics of the far-wake. The system of vortices in the near-wake became unstable and broke down due to wake instability at a distance of five rotor diameters downstream of the wind turbine. This was defined as the boundary between the near-and far-wake regions. The collapsed spiral wake was found to spread in all directions in the far-wake resulting in the formation of the two pairs of counter-rotating vortices which caused the gradual increase of turbulence in these regions. The turbulence intensity in the wake was observed to increase immediately behind the turbine with a maximum of 12.12% at a distance of three rotor diameters downstream of the turbine, after which a gradual decrease in the turbulence intensity was observed in the near-wake regions due to wake instability. However, in the far-wake regions, due to counter-rotating vortices formed by the wake instability, the turbulence intensity showed a tendency to increase intensity. Finally the time-averaged wake velocities from the LES, with and without the blockage corrections, were compared with WAsP and a comparatively good agreement for the axial velocity predictions was observed in the far-wake. Blockage correction; Numerical wind tunnel number of researchers have used CFD, based on the RANS equations to acquire comparatively fast results (Menter et al, 2006; Potsdam and Mavriplis, 2009; Sørensen et al, 2002b). Others have used LES to simulate the wake flows without the turbines, combined with the actuator line and disc methodologies (Wu and Porté-Agel, 2011). However, the approach of "return to the basics" as proposed by Vermeer et al is highly valuable, in that it provides the opportunity to study the aerodynamics of the wind turbines in controlled environments like wind tunnels. The objective of this investigation is to achieve a better understanding of the turbulent wake characteristics behind the wind turbine (NREL Phase VI wind turbine) that was tested in the NASA Ames 24.4 m by 36.6 m wind tunnel. For this, LES was carried out using the commercial CFD code, ANSYS FLUENT 13. The results of the LES have been compared with the aerodynamics of the wind turbine blade that were obtained experimentally by the NREL (Hand and Simms, 2001;. Particular emphasis has been placed on the study of the distribution of the overall wake structure, time-averaged axial velocity (corresponding to velocity deficit) and the increased turbulence intensity in cross-sectional planes perpendicular to the axis of the wake at uniform incoming velocity. The study will be useful for the designers to plan and design future wind farms for the purpose of improvement of the overall wind farm efficiency and the fatigue life of the wind turbines. It also provides understanding of the turbulent wake characteristics of a wind turbine and the much needed results required for validation of turbine wake models. For this reason, the results of LES were also compared with the simple equations provided by WAsP to estimate the wake velocities in the far-wake.

Experimental characterisation of the wake behind paired vertical-axis wind turbines

Journal of Wind Engineering and Industrial Aerodynamics, 2020

Two vertical-axis wind turbines (VAWTs) benefit from a power increase when placed side by side in close proximity. To study the potential of paired VAWTs for integration in wind farms, wind tunnel wake measurements of lift-driven VAWTs are compared for isolated and three counter-rotating configurations. Because the wake of an isolated VAWT is deflected, the direction of rotation significantly influences the wake of paired VAWTs. The wake of counter-rotating VAWTs where the adjacent blades move downwind, exhibits a similar length, width and replenishment as the wake of an isolated VAWT. The wake of counter-rotating VAWTs with adjacent upwind moving blades, however, significantly differs from an isolated VAWT wake. While its wake length is similar to an isolated VAWT wake, its width and replenishment are not. Because of appealing wake characteristics, paired VAWTs exhibit unique advantages for wind farm applications, and especially for offshore floating wind farms.

Study the Impact of Wake on the Arrangement and Economic of Variable Speed Wind Farm

This paper focuses on arrangement and operation of variable speed wind farm. Also, it studies the wake effects on the power production from wind farm by using Jensen's wake model. This methodology can be done by using Matlab program. The objective of every wind farm designer is producing maximum, as possible of energy, with minimal cost of installation. The optimization is done by the minimum cost per unit of energy produced. In this study an algorithm has been developed to solve the rule of thumb a wind farm layout based on the wake model of Jensen. It has the capacity to estimate the optimal number of total power produced in wind farm, in comparison with predominant wind farm. Five different wind turbine types have been used.