Wind tunnel experiments on wind turbine wakes in yaw: Effects of inflow turbulence and shear

Bartl, Jan; Mühle, Franz; Schottler, Jannik; Sætran, Lars Roar; Peinke, Joachim; Adaramola, Muyiwa S.; Hölling, Michael

doi:10.5194/wes-2017-59

Cited by 3 publications

(8 citation statements)

References 14 publications

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“…Together with the inflow-dependent wake flow measurements on the same experimental setup presented in Bartl et al (2018), this study completes the link between detailed wake flow characteristics and power, yaw moments and thrust forces on a turbine operated in the wake.…”

mentioning

confidence: 96%

“…In this experiment T2 is controlled to its optimum power point, which strongly varies for different positions and upstream turbine operational parameters. The exact geometry and detailed performance curves of T1 are described in Bartl et al (2018), while T2's characteristics can be found in Bartl and Saetran (2017). In contrast to most other turbines, the investigated model turbines rotate counter-clockwise.…”

Section: Wind Turbine Modelsmentioning

confidence: 99%

“…The downstream turbine shows the exactly same operating characteristics when operated in undisturbed inflow. For measurements showing the power and thrust coefficient depending on the tip speed ratio λ T 1 it is referred to Bartl et al (2018).…”

Section: Operating Characteristics Of T1mentioning

confidence: 99%

“…The wind tunnel 5 width measures about three times the turbine's rotor diameter, which leaves sufficient space for lateral wake deflection and offset positions for T2. However, a speed-up of the flow in free-stream areas around the rotors is observed due to blockage effects as described in detail in Bartl et al (2018).…”

mentioning

confidence: 99%

“…It is observed that an increase in inflow turbulence results in the same performance characteristics. As discussed by Bartl et al (2018), the decrease in power coefficient can be approximated C P,γ T 1 =0 · cos shows an almost linear behavior around the origin. However, minor asymmetries between positive and corresponding negative yaw angles are observed.…”

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confidence: 99%

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Wind tunnel study on power and loads optimization of two yaw-controlled model wind turbines

Bartl

Mühle

Sætran

2018

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Abstract. In this experimental wind tunnel study the effects of intentional yaw misalignment on the power production and loads of a downstream turbine are investigated for full and partial wake overlap situations. Power, thrust force and yaw moment are measured on both the upstream and downstream turbine. The influence of inflow turbulence level and streamwise turbine separation distance are analyzed for full wake overlap situations. For partial wake overlap the concept of downstream turbine yawing for yaw moment mitigation is examined for different lateral offset positions. 5Results indicate that upstream turbine yaw misalignment is able to increase the combined power production of the two turbines for both partial and full wake overlap setups. For aligned turbine setups the combined power is increased between 3.5% and 11% depending on the inflow turbulence level and turbine separation distance. The increase in combined power is at the expense of increased yaw moments on both upstream and downstream turbine. For partial wake overlap situations, yaw moments on the downstream turbine can be mitigated through upstream turbine yawing, while simultaneously increasing the combined 10 power production. A final test case demonstrates the concept of opposed downstream turbine yawing in partial wake situations, which is shown to reduce its yaw moments and increasing its power production by up to 5%.

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mentioning

confidence: 96%

Section: Wind Turbine Modelsmentioning

confidence: 99%

Section: Operating Characteristics Of T1mentioning

confidence: 99%

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confidence: 99%

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Wind tunnel study on power and loads optimization of two yaw-controlled model wind turbines

Bartl

Mühle

Sætran

2018

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Blind test comparison on the wake behind a yawed wind turbine

Mühle¹,

Schottler²,

Bartl³

et al. 2018

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This article summarizes the results of a fifth Blind test workshop, which was held in Visby, Sweden, in May 2017.This study compares the numerical predictions of the wake flow behind a model wind turbine operated in yaw to experimental wind tunnel results. Prior to the work shop, research groups were invited to predict the turbines' performances and wake flow properties using computational fluid dynamics (CFD) methods. For this purpose, the power, thrust and yaw moments for a 30 • yawed model turbine as well as the wake's mean and turbulent streamwise and vertical flow components were measured 5 in the wind tunnel at the Norwegian University of Science and Technology (NTNU). In order to increase the complexity, a non-yawed downstream turbine was added in a second test case, while a third test case challenged the modelers with a new rotor and turbine geometry. Four participants submitted predictions using different flow solvers, three of which were based on Large Eddy Simulations (LES) while another one used an Improved Delayed Detached Eddy Simulation (IDDES) model. The performance of a single 10 yawed turbine was fairly well predicted by all simulations, both in the first and third test case. The scatter in the downstream turbine's performance predictions in the second test case, however, was found to be significantly larger. The complex asymmetric shape of the mean streamwise and vertical velocity was generally well predicted by all the simulations for all test cases.The largest improvement with respect to previous Blind tests is the good prediction of the levels of turbulent kinetic energy in the wake, even for the complex case of yaw misalignment. These very promising results confirm the mature development 15 stage of LES/DES simulations for wind turbine wake modeling, while competitive advantages might be obtained by faster computational methods.

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Wind tunnel experiments on wind turbine wakes in yaw: redefining the wake width

et al. 2018

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Abstract. This paper presents an investigation of wakes behind model wind turbines, including cases of yaw misalignment. Two different turbines were used and their wakes are compared, isolating effects of boundary conditions and turbine specifications. Laser Doppler anemometry was used to scan full planes of wakes normal to the main flow direction, six rotor diameters downstream of the respective turbine. The wakes of both turbines are compared in terms of the time-averaged main flow component, the turbulent kinetic energy and the distribution of velocity increments. The shape of the velocity increments' distributions is quantified by the shape parameter λ2. The results show that areas of strongly heavy-tailed distributed velocity increments surround the velocity deficits in all cases examined. Thus, a wake is significantly wider when two-point statistics are included as opposed to a description limited to one-point quantities. As non-Gaussian distributions of velocity increments affect loads of downstream rotors, our findings impact the application of active wake steering through yaw misalignment as well as wind farm layout optimizations and should therefore be considered in future wake studies, wind farm layout and farm control approaches. Further, the velocity deficits behind both turbines are deformed to a kidney-like curled shape during yaw misalignment, for which parameterization methods are introduced. Moreover, the lateral wake deflection during yaw misalignment is investigated.

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Wind tunnel experiments on wind turbine wakes in yaw: Effects of inflow turbulence and shear

Cited by 3 publications

References 14 publications

Wind tunnel study on power and loads optimization of two yaw-controlled model wind turbines

Wind tunnel study on power and loads optimization of two yaw-controlled model wind turbines

Blind test comparison on the wake behind a yawed wind turbine

Wind tunnel experiments on wind turbine wakes in yaw: redefining the wake width

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