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A2e Meso-Micro

The objectives of the Mesoscale-Microscale Coupling benchmarks are the creation, assessment, and validation of state-of-the-science atmospheric simulation methodologies to incorporate important environmental drivers of microscale flow characteristics into microscale wind plant simulations.  These improvements are aimed at improving the wind energy industry’s predictive capability. The investigations will utilize a series of case studies culled from several recent and current observational campaigns, incorporating increasingly complex meteorology, topography and terrain conditions.  These include the SWiFT site in Texas, the WFIP II site in the US Pacific Northwest, and data from the New European Wind Atlas. 

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Alaiz

Data Provider: 

Javier Sanz Rodrigo (CENER)

Data accesibility: 

The test case is offered to participants of the IEA Task 31 Wakebench that accept the data licensing agreement attached to this document.

Site Description: 

The Alaiz mountain range is located in Navarre (Spain), around 15 km SSE from Pamplona. The prevailing wind directions are from the North and from the South. To the North a large valley is found at around 700 m lower altitude. To the South, complex terrain is found with the presence of some wind farms, the closest one situated 2 km behind the row of six wind turbine stands of the test site. Five reference met masts, 118 m tall, are located in front of the turbine positions at a distance of around 250 m.

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Alaiz Neutral

Scope

The benchmark is open to participants of the Wakebench project using flow models over topography in neutral conditions. This benchmark is a follow up of the sensitivity analysis (Alaiz_Sensitivity) to validate the results in neutral conditions.

Objectives

Produce the best estimate of the flow field in neutral conditions above the Alaiz site for the North and South wind directions.

Data Accessibility

The benchmark is offered to participants of the IEA Task 31 Wakebench who has signed the NDA attached to the test case guide.

Input data

The conditions for simulating the Alaiz flow field in neutral conditions are:

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Alaiz Sensitivity

Scope

The benchmark is open to participants of the Wakebench project using flow models over topography in neutral conditions. This initial benchmark will carry out an assessment of the sensitivity to modeling criteria that is adopted when approaching the simulation of a realistic site for wind farms in complex terrain. In order to simplify the analysis, only the North and South wind direction sectors will be analyzed.

Objectives

Carry out sensitivity tests on different elements of the modeling chain that require user-dependent decisions: domain dimensions, mesh type and resolution, roughness definition, and wind direction binning (1).

Data Accessibility

The benchmark is offered to participants of the IEA Task 31 Wakebench who has signed the NDA attached to the test case guide.

Input data

The conditions for simulating the Alaiz flow field in neutral conditions are:

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Alpha Ventus

Site Description: 

Data Provider: 

The manufacturers Adwen and Senvion

Data accesibility: 

All data confidential and only on request; construction data have a higher confidentiality level than measurement data.

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Askervein

Data Provider: 

The data have been extracted from Taylor and Teunissen (1983, 1985) reports, available from York University.

Data accesibility: 

The test case is offered to participants of the IEA Task 31 Wakebench. In the future it will be open for public access.

Site Description: 

The Askervein hill project can be considered the cornerstone of boundary layer flow over hills. It is based on two filed campaigns conducted in 1982 and 1983 on and around the Askervein hill, a 116 m high (126 m above sea level) hill on the west coast of the island of South Uist in the Outer Hebrides, Scotland. The hill is isolated in all wind directions but the NE-E sector. To the SW there is a flat uniform fetch of 3-4 km to the coastline where there are sand dunes and low cliffs. A uniform roughness of 0.03 m is assumed all over the hill.

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Askervein Neutral

Scope

The benchmark is open to participants of the Wakebench project using flow models over topography in neutral conditions. The study will show the changes in the mean flow field above the Askervein hill for different incident flow angles defined by the following wind directions:

  • 210º, perpendicular to the long axis of the hill (classical reference),
  • 130º, parallel to the long axis, and
  • 90º, in the wake of upstream hills.

Objectives

Test model fine-tuning strategies that will be applied in complex terrain sites. Evaluate turbulence models in a test site with reasonably well defined boundary conditions. Evaluate the ability of the models to predict wind direction variations close to the ground induced by local topography.

Data Accessibility

The benchmark is offered to participants of the IEA Task 31 Wakebench.

Input data

The conditions for simulating the Askervein flow field in neutral conditions are:

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Atmospheric

Microscale range comprises a wind farm and its local site characteristics. While the flow field is nevertheless modulated by the larger scales of the wind climate, we focus on local topographic and wind turbine generated mean flow and turbulence.


From the wake modeling point of view the microscale models focus on predicting the far-wake behavior and overlapping of multiple wakes in a wind farm array, essential physics to predict the array wake efficiency. This far-wake approximation is justified when the separation between turbines in the streamwise direction is more than 3 to 5 rotor diameters, depending on incoming turbulence. At this distance the wake does not depend so much on the rotor design and engineering models can be designed based on the rotor dimensions and operating conditions defined by the manufacturers power and thrust curves.

Microscale model clasification
Figure 1: Diagram for microscale wind farm model classification

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AVATAR

The EU FP7 project AVATAR was started by an EERA (European Energy Research Alliance) consortium in November 2013. The project lasts 4 years and is carried out by the following consortim consisting of 11 research institutes and two industry partners:

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Axisymmetric Wake

Data Provider: 

Literature.

Data accesibility: 

The theoretical results are taken from papers by Johansson et al. (2003) and Johansson and George (2006). Earlier analyses yielded similar results but did not identify the conditions (downstream location and Reynolds number) for which the results are valid. The test case is offered to participants of the IEA Task 31 Wakebench. In the future it will be open for public access.

Site Description: 

The behavior of the turbulent axisymmetric wake has been considered theoretically for years.

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Axisymmetric Wake Neutral

Scope

The benchmark is open to participants of the Wakebench project using flow models to calculate wind turbine wakes. Completion of the benchmark will demonstrate that a simulation approach is capable of capturing the physics necessary to predict behavior of an isolated wake.

Objectives

Evaluate models using a theoretical solution to assure that they can capture an important component of wind turbine wake flows.

Data Accessibility

The benchmark is offered to participants of the IEA Task 31 Wakebench. In the future it will be open for public access

Input data

The wake profiles being compared should meet the following criteria required for equilibrium similarity:

  • x/θ > 100, and
  • U0δ*/ν > 500

Validation data

The validation exercises to be performed consist of the following comparisons.

  • Demonstrate the wake width grows as x1/3

Note that a is an adjustable parameter that depends on a particular simulation boundary conditions

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Bolund

Data Provider: 

Andreas Bechmann (DTU)

Data accesibility: 

The available test case data was released by RisøDTU as part of the Bolund blind model intercomparison workshop, celebrated in December 2009 at Riso's premises in Roskilde (Denmark).

Site Description: 

Bolund is a 12 m high, 130 m long and 75 m wide isolated hill situated to the North of RisøDTU in Roskilde Fjord, Denmark. It is surrounded by water in all directions except to the E, where a narrow isthmus leads to the mainland. The hill is characterized by a uniform roughness of 0.015 m and surrounded by water with a roughness length of 0.0003 m.

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Bolund Neutral

Scope

The benchmark revisits the blind test of 2009 now allowing the participants to optimize their models to obtain the best match to the validation dataset.

Objectives

Test model fine-tuning strategies that will be applied in complex terrain sites. Evaluate turbulence models in a test site with well defined boundary conditions.

Data Accessibility

The benchmark is offered to participants of the IEA Task 31 Wakebench.

Input data

The conditions for simulating the Bolund flow field in neutral conditions are:

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ECN Wind Turbine Test Station Wieringermeer (EWTW)

Site Description

The ECN Wind Turbine Test Station Wieringermeer (EWTW) is a test location for wind turbines that comprises of six prototype turbines, five research N80 turbines and five large meteorological masts.

Data Provider

ECN Wind Turbine Test Site Wieringermeer

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