Speed Up Effects:

Tunnel Effect

As experienced during a walk between tall buildings in a narrow street, wind speeds are greater in narrow mountain passes. This can be explained by the fact that the air is compressed on the windy side of the mountains, and then its speed increases substantially between the obstacles to the wind. This phenomenon is know as the tunnel effect. Placing a wind turbine in such a tunnel can considerably increase the energy produced thanks to higher wind speeds than in the surrounding areas. But to obtain an efficient tunnel effect, the tunnel must be even and smooth because high levels of roughness (like with hills) can create lots of turbulence and whirls in the tunnel, which can eventually cancel the positive aspect of the tunnel while creating dangerous tear and wear on the wind turbine.

Hill Effect

Placing wind turbines on hills or ridges overlooking the surroundings is a common thing. Indeed this technique allow to have a free view in the prevailing wind direction. Moreover, wind speeds are generally higher on hills than in the surrounding area. This can be explained by the fact that the wind is compressed on the windy side of the hill, and once the air reaches the ridge it can expand again as its soars down into the low pressure area on the other side of the hill. But as usual, if the hill is steep or has an uneven surface, the turbulence will become significant, which could negate the advantage of higher wind speeds.

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