Its transient behaviour and many recirculation zones place Bolund in a category in which the linear flow theory is not applicable.Īthanassiadou M, Castro IP (2001) Neutral flow over a series of rough hills: a laboratory experiment. On the lee side of Bolund, recirculation occurs with the turbulence intensity remaining significantly enhanced even at one hill length downstream. From the wind energy context, this implies that the best site for erecting a turbine based on resource constraints unfortunately also imposes a penalty of high dynamic loads.

A closer inspection reveals transient behaviour with recirculation zones. Depending on the wind direction, we find a maximum speed-up of 30% at the hill top accompanied by a maximum 300% enhancement of turbulence intensity. The nearly perfect upstream conditions are important in forming a meaningful quantitative description of the flow over the Bolund hill. With a 7-km fetch over water, the incoming flow is characterized as flow over flat terrain with a local roughness height based on the surface momentum flux.

We have carefully investigated the upstream conditions. Because of its small size the effect of atmospheric stratification can be neglected, which makes the Bolund experiment ideal for the validation of neutral flow models and hence model scenarios most relevant to wind energy. The physical shape of Bolund represents, in a scaled-down form, a typical wind turbine site in complex terrain. Bolund is a small isolated hill exhibiting a significantly steep escarpment in the main wind direction. We present an analysis of data from a measurement campaign performed at the Bolund peninsula in Denmark in the winter of 2007–2008.

Steep over download