Novel CFD approach for simulation of an ABL wind tunnel flow: validation and application to a FOWT model

Abstract. When comparing Large Eddy Simulations with wind tunnel experiments, choosing the appropriate boundary conditions is crucial to ensure an accurate representation of wind flow. This becomes particularly challenging for Atmospheric Boundary Layer (ABL) wind tunnels, which frequently incorporate calibrated obstacles to replicate the appropriate model-scale ABL flow. Although many researchers prefer to include these elements within the CFD domain, this approach leads to high computational costs and the necessity for precise replication of each obstacle. Alternatives to avoid this high computational cost typically include slip boundary conditions at the top, leading to fast decay in turbulence quantities near the ground. In this study, the authors propose a new methodology based on the precursor technique, which is commonly used for full-scale ABL simulations, combined with a stress top boundary condition. The method is validated against experimental measurements showing significant improvement in the inlet flow quality, when compared to previous methods.

Floating Offshore Wind Turbines (FOWT) are expected to experience significant growth in the coming decades. However, due to the effect of platform motions, their wake structures can be challenging to predict. As a second part of this study, the novel technique is applied together with an actuator disk to represent an oscillating wind turbine model, designed to study FOWT wakes. Simulations with varying turbulence intensities and motion frequencies are conducted. The results corroborate previous findings that the near wake is not significantly influenced by surge motion frequency, although certain frequency cases exhibit more persistent coherence structures than others, which results in a slower wake recovery. This phenomenon is found to be less significant in the context of higher turbulence intensities.