Numerical study of humidity effects in fully developed wind-turbine array boundary layers

Abstract

Wind power is one of the fastest growing energy sources in the world, resulting in increasingly larger surface areas occupied by wind farms. As wind farms become more extended, they start to interact with the atmospheric boundary layer, reducing the available wind speed at turbine hub height (Calaf, Meneveau, Meyers 2010), and altering the air temperature and humidity near the surface (Calaf, Parlange, Meneveau 2011). Turbulence on the other hand, is affected by humidity. This master thesis aims modelling the effect of humidity in fully developed wind turbine array boundary layers. An existing Large-Eddy Simulations (LES) code is generalized to allow the inclusion of moisture. The resulting LES code can be used to study the effect of a large wind farm on the atmospheric boundary layer in presence of moisture. By one hand, the results show that inclusion of moisture generates a slight increase of velocity. Turbulence and hence a slight increase of the shear stresses could take place, but the results are not strong enough to draw this conclusion. Further research is needed on this matter. By the other hand, the combination between both wind turbines and moisture (when moisture is coupled to momentum and positive moisture flux is considered) modifies the moisture flux, decreasing its absolute value. Hence, the inner layer lets escape less amount of moisture to the free atmosphere if moisture interactions are taken into account. Only one case has been studied in this thesis, therefore further research in order to affirm these findings is needed.