Comparative Analysis of the Effect of Two Tower Geometries on Offshore Wind Turbine Wake Aerodynamics

Rotor-wake interactions and the corresponding power losses are a significant aspect to account in the development and design of new offshore wind farms. Indeed, the wake shed by upstream turbines can induce substantial reduction in the power generated by the downstream turbines. To mitigate this effect, turbines are located at considerable relative distances, allowing the downstream flows with larger space to recover kinetic energy from the freestream flow field. The mechanism of wake recovery is an interesting area of study for wind engineering, being affected by various factors such as mixing with atmospheric and ground turbulence, interaction of the wake flow and tip vortices with fixed structures and obstacles, possible turbulence production driven by dedicated blade refitting. In this paper, we examine the impact of support structures on downstream turbulent flow and wake recovery for a utility-scale wind turbine operating in offshore environment. We use the actuator line method to model the rotor, a common approach in simulating wind farms with CFD solvers, while the support structures geometry given by the tower and nacelle is directly resolved by the CFD mesh. The CFD simulation is based on the incompressible k-ω SST-IDDES model, which is a hybrid LES/RANS turbulence model with enhanced wall-modeling capabilities. The numerical modeling is implemented in OpenFOAM and in a dedicated library for the actuator line model to simulate the blade’s aerodynamics. This is further augmented with a finite element model to account for blade elasticity. In the presented investigation, we use the IEA-15MW turbine model. The rotor is mounted on two distinct types of towers: a standard mono-pylon tower and a tripod-style tower.