Nested numerical simulation of multi-scale flow characteristics around monopile foundation of offshore wind farm at Weihai coastal water, China

When constructing an offshore wind farm under tidal current conditions, flow field characteristics without structures are often used for design. However, the presence of structure will greatly affect the flow field around structures. Therefore, it is important to study the flow characteristics around the wind farm foundations under the tidal flow conditions to ensure safe construction and operation. Due to the spatial-temporal scale differences of different physical processes, it is difficult to apply the existing numerical models to accurately simulate the flow characteristics around the offshore monopile. Therefore, this study will link the large-scale TELEMAC with the small-scale OpenFOAM code to establish a multi-scale spatial nesting model to consider the temporal and spatial flow characteristics of real ocean environmental conditions. The nested model is validated using the measurements. The validated model is then applied to conduct some parametric study to evaluate the effect of the wind speed and direction and tidal flow on the flow characteristics around the monopile. Results reveal that the tidal flow velocity could be significantly suppressed by strong opposite wind and vice versa. Tidal flow separation occurring at the lee side of the pile generates the so-called von Karman vortex street downstream of the pile.