Barthelmie, RJ

More documents

Recommendations

Info

Presented at the European Wind Energy Conference and Exhibition, July 2001, Copenhagen Bockstigen in Sweden (Figure 1). Data from Horns Rev in Denmark will be used in the evaluation stage of the project. 58 Lat N 57 56 55 Horns Rev Denmark Vindeby Sweden Bockstigen 8 9 10 11 12 13 14 15 16 17 18 19 Longitude E Velocity deficit at 38 m height at Vindeby (m/s) 1.2 0.8 0.4 Vindeby data Fit through origin Y = 0.229 * X Figure 1. Locations of the offshore wind farms at Vindeby and Bockstigen and the planned wind farm at Horns Rev. 0 0 1 2 3 4 5 Number of wakes Both wind farms are located close to the coast but Vindeby is a relatively sheltered location in shallow water (2-5m) while Bockstigen is in deeper water. The monitoring systems are also very different. Vindeby has three masts one on the coast and two offshore providing a free stream wind speed for all wind directions (Figure 2) [1] whereas the offshore mast at Bockstigen is in the centre of the wind farm. In addition to providing case studies for the offshore wake modelling, a new database of one-minute data has been provided for Vindeby (data from 1994-95). More than 400,000 simultaneous observations from the three masts have been analysed to examine wind and turbulence characteristics in different wake and meteorological conditions. 5 wakes to SMS 1W 1E 2W SMW 2E 3W 3E 2 wakes to SMW 4W 4E 5W 5E SMS 2 wakes to SMW 6E 1 wake to SMS Figure 2. Layout of the wind farm at Vindeby (• shows each wind turbine and ▲ the two sea masts). Using all available observations the average velocity deficit at hub-height (38m) has been calculated for one, two and five wakes at Vindeby. The results shown in Figure 3 illustrate the relationship between the average velocity deficit and the number of wakes at a distance of 8.5 rotor diameters. Note that this relationship also depends on the wind turbine and the average meteorological conditions at each site. Figure 3. Relationship between velocity deficit and the number of wakes at Vindeby. 2.2 Comparison of wake models The partners performing wake modelling within the project and a brief description of the models are given in Table 1. To evaluate wake model performances, the first approach used was to identify case studies at both sites but this was not sufficiently comprehensive. Hence a systematic range of 48 case studies was identified to cover the expected range of conditions (Table 2) at Vindeby. To date, the single wake case for the Vindeby wind turbine 6E (rotor diameter 35 m, hub height 38) and single wake case studies at Bockstigen have been performed. The wake model performance and comparison with data is given in [2]. In the next stage, multiple wakes at Vindeby will be investigated in parallel with wake model development based on the results of the first two workpackages. Table 1. Description of the wake models being used for the offshore evaluation Partner Risoe National Laboratory Uppsala University Brief description of wake model 1) Axisymmetric engineering model 2) CFD using k-ε turbulence closure coupled to an aeroelastic model Velocity deficit model using the transport time for the wake development Garrad Hassan Axisymmetric numeric Navier Stokes, eddy-viscosity closure (Windfarmer) Robert Gordon University Fully elliptic 3D turbulent Navier Stokes with k-ε turbulence model Oldenburg University Axisymmetric numeric Navier Stokes, eddy-viscosity closure Netherlands Energy Research Foundation Parabolized 3D Navier Stokes, k- ε turbulence model
Presented at the European Wind Energy Conference and Exhibition, July 2001, Copenhagen Table 2. Wake model scenarios (48 in total) Parameter Wind speed (m/s) Turbulence Intensity (%) Atmospheric stability (Monin- Obukhov in m) Scenarios 5 7.5 10 15 6 8 10 15 Neutral ±1000 m Stable >0,
Page 1: Presented at the European Wind Ener

Barthelmie, RJ

Create successful ePaper yourself

Delete template?

Save as template?