Abstract
Complex terrain can influence wind turbine wakes and wind speed profiles in a wind farm. Consequently, predicting the performance of wind turbines and energy production over complex terrain is more difficult than it is over flat terrain. In this preliminary study, an engineering wake model, that considers acceleration on a two-dimensional hill, was developed based on the momentum theory. The model consists of the wake width and wake wind speed. The equation to calculate the rotor thrust, which is calculated by the wake wind speed profiles, was also formulated. Then, a wind-tunnel test was performed in simple flow conditions in order to investigate wake development over a two-dimensional hill. After this the wake model was compared with the wind-tunnel test, and the results obtained by using the new wake model were close to the wind-tunnel test results. Using the new wake model, it was possible to estimate the wake shrinkage in an accelerating two-dimensional wind field.
Highlights
Wind speed decreases as upstream wind turbines extract wind kinetic energy in a wind farm.As a consequence, the power output of downstream turbines drastically decreases [1,2]
Uchida et al [9] show that the pitch control of a wind turbine is incapable of reacting properly to the wind speed variation that resulted from the terrain upstream of the wind farm
Hyvärinen and Segalini [27,28] studied wind turbine wake development over sinusoidal hills through a wind-tunnel test and numerical simulations, and the results show a faster wake recovery over the hilly terrain
Summary
Wind speed decreases as upstream wind turbines extract wind kinetic energy in a wind farm. Cao and Tamura [19] performed wind-tunnel tests to investigate the surface roughness effects on the flow over a two-dimensional steep hill, and the study shows that the speed-up ratio at the top of a rough hill is greater than that of a smooth hill, and the flow separation region of a rough hill extends farther downstream than that of a smooth hill. Cao and Tamura [21] performed wind-tunnel tests to examine the effects of roughness blocks on the flow over a two-dimensional hill, and the study suggests that the velocity deficit and turbulence structure downstream of the hill are significantly affected by the number and location of roughness blocks on the hill surface or the upstream of the hill.
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