Room:
Diesel Hall
Topic:
B. Wind, wakes, turbulence and wind farms
Form of presentation:
Oral
Duration:
120 Minutes
Chaired by: J. Meyers, J. Peinke
10:30
Wake effects between two neighbouring wind farms
Dr. Nicolai Gayle Nygaard | DONG Energy Wind Power | Denmark
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Authors:
Dr. Nicolai Gayle Nygaard | DONG Energy Wind Power | Denmark
Sidse Damgaard | Denmark
We address the issue of wake effects between two neighbouring offshore wind farms by analysing simultaneous production data from Rød Sand II and Nysted. The upstream wind farm is found to not just perturb the flow in its wake, but also to cause speed-ups at the positions of some downstream turbines. We use the data to perform a validation of a simple wake model for flow cases corresponding to wind directions of maximum internal and external wake effects.
10:50
Long-wave instabilities in the wake of a two-bladed rotor
Umberto Quaranta | Airbus Helicopters | France
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Authors:
Umberto Quaranta | Airbus Helicopters | France
Mattias Brynjell-Rahkola | France
Dan Henningson | France
We present a comparison between experimental observations and theoretical predictions concerning long-wave displacement instabilities of the helical vortices in the wake of a two-bladed rotor. Experiments are performed with a small-scale rotor in a water channel, using a set-up that allows the individual triggering of various instability modes at different azimuthal wave numbers, leading to local or global pairing of successive vortex loops. The initial development of the instability and the measured growth rates are in good agreement with the predictions from linear stability theory, based on an approach where the helical vortex system is represented by filaments. At later times, local pairing develops into large-scale distortions of the vortices, whereas for global pairing the non-linear evolution returns the system almost to its initial geometry.
11:10
Why the Coriolis force turns a wind farm wake to the right in the Northern Hemisphere
Dr. Paul van der Laan | Technical University of Denmark | Denmark
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Authors:
Dr. Paul van der Laan | Technical University of Denmark | Denmark
Niels Sørensen | Denmark
The interaction between the Coriolis force and a wind farm wake is explained by Reynolds-Averaged Navier-Stokes simulations, using two different wind farm representations: a high roughness and 5x5 actuator disks. Surprisingly, the calculated wind farm wake deflection is opposite in the two simulations. A momentum balance in the cross flow direction shows that the interaction between the Coriolis force and the 5x5 actuator disks is complex due to turbulent mixing of fresh momentum from above into the wind farm, which is not observed for the interaction between the Coriolis force and a roughness change.
11:30
Characterization of wind velocities in the wake of a full scale wind turbine using three ground-based synchronized WindScanners
Hasan Yazicioglu | Technical University of Denmark | Denmark
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Authors:
Hasan Yazicioglu | Technical University of Denmark | Denmark
Nikolas Angelou | Denmark
Torben Mikkelsen | Denmark
Juan José Trujillo | Denmark
We present 3D wind vector field measurements obtained in the near-wake region behind a 40 m rotor diameter full-scale test turbine (NEG Nordtank) using three ground-based synchronised short-range WindScanners. The 3D wind velocity field is reconstructed in in horizontal and vertical scan planes. The 10-min mean values of the three wind components reveal detailed information regarding the wake properties while propagating downwind over flat terrain, valuable for comparison with CFD. Furthermore, the wake centre is tracked from the measurements and its meander is investigated as function of the turbine's yaw misalignment. The centre line wake deficit is calculated both in a Nacelle Frame of Reference (NFoR) and in a Moving Frame of Reference (MFoR).
11:50
The effect of the number of blades on wind turbine wake – a comparison between 2-and 3-bladed rotors
Franz Mühle | NMBU Ås | Norway
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Authors:
Franz Mühle | NMBU Ås | Norway
Muyiwa Samuel Adaramola | Norway
Lars Roar Sætran | Norway
Due to cost benefit and weight reduction, 2-bladed wind turbines have the potential to become more important for offshore wind applications. In order to optimize the arrangement of wind turbines in wind farms and for accurate forecasts of the power production, a detailed knowledge of the wake flow is needed. In this study, three different rotors with varying number of blades and similar performance behaviour have been designed and manufactured using the 3-dimensional (3D) printing technology. The performance characteristics of these rotors as well as their wake features are measured experimentally in wind tunnel tests and compared. The velocity deficit is seen to vary only insignificantly for the wakes in distances of 3D (where D is the rotor diameter), 5D and 7D behind the turbine. However, higher turbulence intensity levels are recorded in the wake of the 2-bladed rotors. This could have potential for a faster wake recovery and thus a narrower turbine spacing.