A numerical study on wind dams: A novel approach to enhance wind potential using natural barriers

Abstract

A natural barrier, such as a hill or a small mountain, might be the location of a great potential for wind energy production. The expression ‘wind dam’ refers to a newly proposed concept which aims to take advantage from the existing geographical natural barriers, in order to generate a high speed wind zone for installation of wind turbines. Previous studies have claimed that excavating a tunnel in a hill, connecting its high pressure zone to the low pressure zone, provides not only a suitable location for wind turbines, but also minimizes the negative environmental and visual impacts of the installed wind turbines. In the current study, the effects of various geometrical parameters on the air flow pattern inside such a tunnel are investigated numerically. The effects of the tunnel inclination angle, converging/diverging angle, entrance shape, tunnel width, incident wind velocity and its profile on the air flow increment inside the tunnel are examined in details. Finding the best shape for the tunnel, the effects of adding a wind turbine inside the tunnel are also analyzed. Results show that the best locations for the beginning and ending of the tunnel are almost the upwind base and the summit, respectively. For a tunnel without any wind turbines mounted in it, the maximum velocity increment is 1.5U∞ which occurs in a 2-degrees diverging tunnel with an initial width of 0.04H, where H is the hill height and U∞ is the incident wind velocity. Investigating the incident wind profile effects showed that the velocity increment in the tunnel is higher at the sites with lower roughness heights. It is also found that a relatively uniform velocity inside the tunnel can be obtained by modifying the inlet shape of the tunnel. Considering the effects of adding a wind turbine inside the tunnel revealed that this turbine can generate at least 50% more energy compared to a bare wind turbine, for the loading coefficients between 0 and 1. However, for the loading coefficients larger than 1.0, the wind dam concept works worse than a bare wind turbine.