Adapted two-equation turbulence closures for actuator disk RANS simulations of wind & tidal turbine wakes

Reliable methods for modelling wake recovery within a farm of wind or tidal turbines are critical for obtaining accurate estimates of annual energy production, and for detailed farm layout optimization. These are important objectives for maximizing energy yield while minimizing costs. Computational fluid dynamics (CFD) simulation is rapidly being adopted as a tool for flow modelling in wind and tidal farms, gaining favour over more traditional and simpler empirically-determined wake models. The most practical methodology for CFD simulations of turbine farms uses an actuator disk (AD) representation for each rotor, which imposes the rotor forces by adding source terms to the governing equations rather than explicitly resolving the flow over the turbine blades. It is well understood that when using the AD approach, standard turbulence models tend to predict faster wake recovery than is observed in real flows. Thus, the standard CFD turbulence models must be adapted for use with the AD methodology. Additionally, because of the manner in which the AD approach distributes the rotor forces, it cannot resolve the system of discrete vortices trailed from the blade tips.