Wake mixing effects of offshore wind-turbine foundations on sea thermal stratification: a circular cylinder case study

Övrigt konferensbidrag, 2025

Offshore wind energy is recognized as a key renewable resource. However, concerns have been raised about the potential hydrographic effects of offshore wind turbine (OWT) foundations on marine ecosystems through alteration of the natural stratification of the shelf sea. If all planned OWT farms in the North Sea are realised, their presence could lead to basin wide disruption of the natural stratification by mixing water layers (Christiansen et al. 2023). The disruption in turn could alter the biogeochemical cycling, primary production and bottom water deoxygenation thereby impacting ecosystem health and fisheries. Previous studies have primarily focused on shallower waters, and the aim of this study was to understand the formation and dispersion mechanisms of wakes from deeper OWT foundations, down to 60 m, in thermally stratified seas. A basic case of a circular cylinder, representing a major component of the foundation, was numerically investigated using high-fidelity computational fluid dynamics (CFD) simulations. The numerical method was the large eddy simulation approach with the wall-adapting local eddy-viscosity (WALE) model. Compared to the non-stratified flow, vertical temperature distribution was found to significantly affect the characteristics of the wake. For example, the transient fields and statistics of the physical quantities such as the velocity, pressure, and temperature. Vertical fluctuations of the velocity in the stratified flow were dampened due to the buoyancy effect, resulting in less mean temperature alteration. The results imply that the wake mixing effects from the OWT foundations are dependent on the vertical temperature distributions in relation to sesions.