Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia StrategyP-20

Steep 2D Hill effect on Vertical Wind Speed Distribution
Omar M. Ibrahim1 and Shigeo Yoshida212

Kyushu University, Interdisciplinary Graduate School of Engineering Sciences
Kyushu University, Research Institute for Applied Mechanics, Kasuga-koen, Kasuga, 816-8580,

Abstract
Complex terrain sites are associated with hard flow conditions. Wind tunnel tests were carried outto investigate the effect of a 2D hill on the vertical wind speed distribution. Experiments wereperformed in the boundary layer wind tunnel to measure the average vertical wind speed
distribution at a number of locations over the 2D hill. Current studies showed the great effect ofthe 2D hill on wind flow.

slope of the hill and equals to 0.45, Z-axis isthe vertical direction, and X-axis is thestreamwise direction.

1. Introduction
Onshore wind farms number has
increased over the last years [1]. Wind farms
are being built over or close to complex
terrains, because possible sites with flat
terrain are already developed. Complex
terrain sites can generate large amounts ofturbulence and high loads on wind turbine
blades [2]. Therefore, wind farm terrain
shape must be considered along with windturbine wake effects during the wind farmlayout optimization process.
This work investigates the effect of a2D hill on the vertical wind speed
distribution. Wind tunnel tests wereperformed in the boundary layer wind tunnel
where the average vertical wind speed
distribution was measured along the hill
without the wind turbine.

[−0.5(𝑍=ℎ 𝑒2𝑋)]
𝐿1.1774(1)

Various measurements were done at the topof the hill in order to make sure that the flow
over the hill is two dimensional. The hillmodel was positioned at a distance from thewind tunnel floor in order to get a uniform
flow condition.
The objective of the wind tunnel test was toexamine the flow over the 2D hill withoutwind turbines, as shown in figure 2. The
inlet wind velocity was constant, and theaverage wind speed distribution wasmeasured using a hot wire anemometer at
six locations over the hill along thestreamwise direction and vertically along theZ-axis.

2. Method

Experiments were performed in theboundary layer wind tunnel of Kyushu
University. The Boundary Layer WindTunnel is a closed circuit type and can beswitched to open circuit if required. The test
section of the wind tunnel is 3.6 m wide, 2m high, and 15 m long. A uniform air flow
with turbulence intensity less than 0.5% canbe achieved in this wind tunnel, and themaximum wind speed is 30 m/s [3]. The 2D
hill is represented by equation (1) andshown in Figure 1. Where h is the height ofthe 2D hill and equals to the diameter of thewind turbine rotor, L equals to h/2S, S is theFigure 1. Schematic diagram of the 2D hill model.

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Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy

P-20

4. Conclusions
This work investigated the effect of a2D hill on the average vertical wind speed
distribution. Experiments were performed in
the boundary layer wind tunnel where theaverage vertical wind speed distribution wasmeasured using a hot wire anemometer
along the hill without the wind turbine at six
locations starting at X = -1560 mm to X =390 mm with an increment of 390 mm. The
results showed the great effect of the steep
hill on the average vertical wind speed
distribution

Figure 2. Wind speed measurements over the hill.
3. Results and discussion

Figure 3 shows the average verticalwind speed distribution over 2D hill at six
locations starting at X = -1560 mm to X =390 mm with an increment of 390 mm. In
figure 3, the vertical axis represents theheight of the wind tunnel test which is equal
to 2m, and the horizontal axis is the windvelocity in (m/s). Wind velocity is almost
constant at X = -1560 mm along theZ-direction, afterwards, wind velocity starts
to increase at X = -780 mm until it reaches
the maximum wind speed at the top of thehill (at X = 0), then starts to decrease at thedownstream of the hill at X = 390 mm.
Figure 3 shows the great effect of the 2D hillon the average vertical wind speed
distribution.

Reference[1] Global Wind Energy Council (GWEC)[2] Politis, E. S., Prospathopoulos, J., Cabezon,D., Hansen, K. S., Chaviaropoulos, P. K. andBarthelmie, R. J. (2012), Modeling wake
effects in large wind farms in complex terrain:
the problem, the methods and the issues. WindEnerg,2012;15(1):
161–182.
doi:10.1002/we.481[3] Wind Engineering Section, ResearchInstitute for Applied Mechanics (RIAM),
Kyushu University.

Email: omaribrahim2006@hotmail.com

Figure 3. Average vertical wind speed distribution
over 2D hill at six locations.

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