Large Eddy Simulation study of a fully developed thermal wind-turbine array boundary layer

Abstract

When wind turbines are arranged in large wind farms, their efficiency decreases significantly due to wake effects and to complex turbulence interactions with the atmospheric boundary layer (ABL) (Frandsen et al., 2006). For large wind farms whose length exceeds the ABL height by over an order of magnitude, a “fully developed” flow regime may be established (Frandsen et al., 2006; Calaf et al., 2010; Cal et al., 2010). In this asymptotic regime, the changes in the stream-wise direction are small compared to the more relevant vertical exchange mechanisms. Such a fully developed wind-turbine array boundary layer (WTABL) has recently been studied (Calaf et al., 2010) using Large Eddy Simulations (LES) under neutral stability conditions. The simulations showed the existence of two log-laws, one above (characterized by: $u_{*}^{hi},\,z_{o}^{hi}$) and one below ($u_{*}^{lo},\,z_{o}^{lo}$) the wind turbine region. This enabled the development of more accurate parameterizations of the effective roughness scale for a wind farm. Now, a suite of Large Eddy Simulations, in which wind turbines are modeled as in (Calaf et al., 2010) using the classical drag disk concept are performed, again in neutral conditions but also considering temperature. Figure 1 shows a schematic of the geometry of the simulation.