Parametrising wakes for oceanographic models

Research projects

Project Description:

This Research Project is part of the Aura CDT’s Predicting Offshore Wind wake interactions for Energy and the enviRonment (POWER) Cluster.

The offshore wind sector is rapidly expanding to meet net-zero energy demands. Individual turbines and farms are getting larger and further from shore, with individual turbines spanning 240 m in diameter and farms reaching 600 km2. Forced by spatial constraints, but enabled by floating technology, farms are now developing in deeper waters, occupying increasingly vast areas.

Oceanographic flow processes are highly sensitive to sea surface boundary conditions (Christiansen et al., 2022), which are in turn critically dependent on atmospheric forcing. Atmospheric flows past offshore wind turbines produce highly turbulent and extensive wakes. These wakes are a necessary result of energy extraction from the wind, and are a key motivation for spatial planning of offshore wind farms where turbine placement is optimized for maximal energy extraction with minimized costs associated to infrastructure and spatial footprint (Giebel et al., 2016). The turbulent wakes propagate downstream, leading to wake-wake interactions and farm-scale atmospheric flow processes with a significantly reduced wind speed in the lee of an offshore wind farm (Platis et al., 2018).

It has been recently shown that such large-scale atmospheric interactions can have a significant effect on sea-surface conditions, realised through a locally reduced wind shear stress (Christiansen et al., 2022). Large-scale deployment of offshore wind farms in shelf seas therefore poses an emerging oceanographic problem; shelf seas are vital for life on and below water through their control on the vertical transport of nutrients, and are a key component of the biogeochemical cycle (van Berkel et al., 2020). These are crucially dependent on general circulation and water column structure, which are both highly sensitive to conditions at the sea surface (Dorrell et al., 2022). Yet the impact of offshore wind expansion on sea surface conditions and subsequent regional scale effects is poorly understood, and has only recently gained research interest. While wake parameterisations for atmospheric models have received significant interest over the last decade, the current state of the art oceanographic models make sweeping assumptions regarding the form of sea-surface forcing, particularly concerning wake-wake interactions, spatial variability, and turbulent modifications (Christiansen et al., 2022). These limitations must be overcome for accurate model predictions of oceanographic response to offshore wind expansion.

This project aims to advance sea-surface parameterisations of atmospheric offshore wind farm wakes for use in oceanographic models, directly supported by the National Oceanography Centre, using the North-West European Shelf FVCOM model. This aim will be realised through the following objectives:

  • Explore literature and gather/generate datasets required for model validation
  • Develop and validate wake parameterisations
  • Explore the influence of solution sensitivity to model parameters
  • Explore the potential impacts of future offshore wind development on North Sea oceanography

Completion of these objectives will deliver a functional oceanographic model for future research into impacts of offshore wind deployment to inform marine spatial planning.

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