INVESTIGATION OF THE BOUNDARY LAYER CHARACTERISTICS OVER COMPLEX TERRAIN. A.M.Loredo-Souza, J.M.L.Mattuella, M.G.K.Oliveira Federal University of Rio Grande do Sul - UFRGS, Porto Alegre, Brazil. Introduction
INVESTIGATION OF THE BOUNDARY LAYER CHARACTERISTICS OVER
A.M.Loredo-Souza, J.M.L.Mattuella, M.G.K.Oliveira
Federal University of Rio Grande do Sul - UFRGS,
Porto Alegre, Brazil
The complex orography presents a specific and local challenge for the wind resource assessment. In order to reduce the uncertainty in the wind resource evaluation this research analyzed and compared six national Wind Codes in order to determine the correlation among them. These standards offer a specific methodology for estimating the speed-up effect in singular topographies. The analytical models included in the study are: American Society of Civil Engineering Standard, ASCE 7-95 (ASCE 7-95); Australian/New Zealand Standard Loading Code AS/NZS 1170.2: 2002; Japanese Code AIJ: 2004; European Standard CEN TC 250: 2002; National Building Code of Canada, 2005, (NRCC 2005); NBR 6123 (1987) and Models, Jackson and Hunt (1975) and Davenport et al. (1988).
Wind-tunnel simulations of the atmospheric stable boundary layer were developed over a rough and smooth surface approaching a scaled model of a complex terrain. The tests were performed at the Boundary Layer Wind Tunnel Prof Joaquim Blessmann of the Federal University of Rio Grande do Sul, Brazil. The surface of the model was scanned at various heights, using hot-wire anemometry. Vertical profiles of the turbulence intensity and the wind speed were generated.
2. Localization: The research were development in Jaburu Hill, placed in Espírito Santo, Brazil, as show Fig 01.
3. Physical Modeling: Boundary Layer Wind Tunnel of the Federal University of Rio Grande do Sul, Brazil
This is a closed return type wind tunnel, with a length/height ratio of the test chamber around 10, being 1.30 m wide, 0.90 m high and 9.32 m long as shown in Fig 02. The highest flow velocity in this camera with smooth uniform wind and without any obstruction exceeds 160 km/h. Figure 03 shows the model inside the wind tunnel during the hot-wire measurements.
4. Calculation methods:
Six major Wind Codes were reviewed and compared: Brazilian Code (1987); American Standard ASCE/SEI 7-05:2005; European Standard CEN TC 250: 2002; Japanese Code AIJ: 2004; Australian/New Zealand Standard AS/NZS 1170.2: 2002 and Canadian Code (2005) 
Thevelocity measurements and the turbulence intensity were obtained for two types of terrain, with a power law exponent p=0,11 and p=0,23 in nine points according coordinates in Figure 04.
Figure 04 Coordinates of measurement points
4.1 Codes Methodology
Espirito Santo State
Annual average Wind Speed (m/s) 50 m Height
Annual average Wind Speed (m/s) 100 m Height
Figure 01 Localization of research
4.2 Codes Results
1. The reference velocities have different criteria in all the standards, regarding the terrain conditions and wind speed interval. The standards may use mean hourly, 10 minutes or 3s gust for their reference wind velocities. In this case, for Codes comparison it is necessary an adequate patronization.
2. For the analytical models considering flat terrain, the results of the NBCC(1995) agree with ASCE/SEI 7-05,2006; the AIJ,2004 agree with CEN TC 250,2002 and the NBR 6123 do not agree with any of the previous, although the differences are not so high.
3. There are significant differences in speed-up effects among the analyzed models. These differences occur for lower and upper limiting slopes, types of topography (hills, ridges and escarpments), and for regions of application of speedup effects, both in the vertical and horizontal extent. This can affect the potential predictions for power estimations in the establishment of wind farms.
Figure 02 Boundary Layer Wind Tunnel Prof. Joaquim Blessmann
AMERICAN STANDARD. ASCE/SEI 7-05, 2006; AUSTRALIAN/NEW ZEALAND STANDARD. AS/NZS 1170.2, 2002; EUROPEAN COMMISION, EUROCODE, CEN TC 250,2002;NBCC(1995), National Building Code of Canada, Ottawa, Canada; JAPANESE CODE. AIJ: Architectural Institute of Japan, 2004.
Figure 03 Topographyc model inside the wind tunnel.
DEWEK 2010 -10th German Wind Energy Conference