Single-turbine scale quantification of wake turbulence

Project Description:

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

Atmospheric wind turbine wakes are a critical control on wind farm layout. Individual wind turbines produce turbulent wakes that have implications for maximum power generation from downwind turbines, increased fatigue loads and associated maintenance costs (Porté-Agel et al., 2020) , as well as environmental issues such as noise generation, and introduction of large-scale, atmospherically forced, hydrodynamic structures A number of studies have investigated this wake turbulence numerically, experimentally and in the field as a function of operational conditions. For example, Howard et al. (2015) examined the wake meandering as a function of turbine operating conditions. This meandering originated with the wake shed from the hub of the turbine but its shape was a function of the tip-speed ratio adopted for the turbine operation, with the mechanism for this attributed to the development and interaction of small-scale coherent structures. Kadum et al. (2019) examined turbine wakes as a function of the pitch of the turbine and found effects varied spatially, with pitch having a discernible impact on wake structure in less turbulent regions, but this being overshadowed by the intermittency resulting from tip vortices in other locations.

This literature and related studies have discovered a number of salient processes and have permitted qualitative guidelines to be formulated regarding phenomena that engineering design needs to be aware of. However, for such information to be useful quantitatively there needs to be:
(1) An explanation of these phenomena in terms of flow physics;
(2) A development of flow modelling methods that can represent these physics

It is these twin objectives that are at the heart of this proposal, which aims to develop a physically based model for computational fluid dynamics’ simulations of turbine wake effects that incorporates an effective parameterisation of these processes. Given that the above studies have demonstrated the relevance of non-local energy transfers for these dynamics, scientific novelty in this project will stem from three interconnected approaches that have been underexplored in the wind turbine literature:
(i) Explicit consideration of non-equilibrium energy scaling for near-field wakes and its implications for subgrid-scale closure;
(ii) The links between non-equilibrium energy transfer and the pressure-Hessian dominated region of the near wake (Paul et al., 2017);
(iii) The link between the large-scale helicoidal wake generation, smaller scale and thus, energy transfer and dissipation and its impact on wake persistence.

By characterising the impact of these effects we will be able to develop an alternative model for modelling turbine wake structure

References
Howard, K.B. et al. 2015. On the statistics of wind turbine wake meandering: An experimental investigation,  Physics of Fluids 27, 075103 doi: 10.1063/1.4923334
Kadum, H. et al. 2019. Wind turbine wake intermittency dependence on turbulence intensity and pitch motion, Journal of Renewable and Sustainable Energy 11, 053302, doi: 10.1063/1.509782
Paul I., Papadakis G., Vassilicos J.C. 2017. Genesis and evolution of velocity gradients in near-field spatially developing turbulence, Journal of Fluid Mechanics 815, 295-332
Porté-Agel, F., Bastankhah, M., Shamsoddin, S. 2020. Wind-Turbine and Wind-Farm Flows: A Review, Boundary-Layer Meteorology 174(1), pp. 1–59