Effect of complex terrain on the performance of wind farms

We use a newly developed wall modeled immersed boundary method for large-eddy simulations to study the performance of wind farms in complex terrain. The method is validated against wind tunnel measurements for flow over a 2D ridge and a 3D hill. First, we analyze the performance of a single wind turbine in the vicinity of a ridge. For turbines that are significantly taller than the ridge, the performance improves as the flow speeds-up over the ridge. The impact of the hill on the performance of short turbines depends on the turbine location. The turbine performance is better at the hilltop. However, the performance of turbines located in front of the ridge is impacted due to blockage effects. Secondly, we consider a wind farm with a ridge in the middle. The ridge wake is very pronounced due to which the performance of turbines located close to the ridge is mainly determined by the flow dynamics induced by the ridge and not by the wind turbine wakes. Thirdly, we find that there is an optimal turbine spacing, which maximizes the wind farm power output, for a wind farm located between two ridges. The reason is that wind turbines should not be placed too close to the hill, while they should also not be placed too close to each other.