Simulating tidal turbines with multi-scale mesh optimisation techniques

Mohammad Amin Abolghasemi,Matthew D Piggott,Johannes Spinneken,Axelle Viré,Colin J Cotter,Sarah Crammond

doi:10.1016/j.jfluidstructs.2016.07.007

Mohammad Amin Abolghasemi, Matthew D Piggott + Show 4 more

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https://doi.org/10.1016/j.jfluidstructs.2016.07.007

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Abstract

Embedding tidal turbines within simulations of realistic large-scale tidal flows is a highly multi-scale problem that poses significant computational challenges. Here this problem is tackled using actuator disc momentum (ADM) theory and Reynolds-averaged Navier–Stokes (RANS) with, for the first time, dynamically adaptive mesh optimisation techniques. Both k−ω and k−ω SST RANS models have been developed within the Fluidity framework, an adaptive mesh CFD solver, and the model is validated against two sets of experimental flume test results. A brief comparison against a similar OpenFOAM model is presented to portray the benefits of the finite element discretisation scheme employed in the Fluidity ADM model. This model has been developed with the aim that it will be seamlessly combined with larger numerical models simulating tidal flows in realistic domains. This is where the mesh optimisation capability is a major advantage as it enables the mesh to be refined dynamically in time and only in the locations required, thus making optimal use of limited computational resources.

Highlights

This study focuses on the extraction of tidal stream energy from coastal waters via horizontal axis tidal turbines which are currently the favoured approach to efficiently harness the vast and reliably predictable tidal resource
Having said that, based on the results presented, there is no disadvantage to using the k − ω Reynolds-averaged Navier– Stokes (RANS) model, as long as appropriate correction terms are introduced to account for the short circuiting of the turbulence cascade
An actuator disc momentum (ADM) model incorporating a momentum sink term and RANS models which can simulate flow past horizontal axis tidal turbines and account for turbulence characteristics has been developed within an adaptive mesh CFD solver

Summary

Introduction

This study focuses on the extraction of tidal stream energy from coastal waters via horizontal axis tidal turbines which are currently the favoured approach to efficiently harness the vast and reliably predictable tidal resource. Maximising the power output of arrays of turbines is essential, but the environmental impacts must be studied and modelled in depth as it is vital to ensure that the efforts to reduce carbon emissions do not result in new environmental concerns. Previous studies have shown that in order to correctly assess the power extraction from tidal turbine arrays, an undisturbed flow approach, termed the flux method (BLACK & VEATCH, 2012), does not suffice and the hydrodynamic influences of the turbines and their wake interactions must be accounted for (Garrett and Cummins, 2007; Whelan et al, 2009; Vennell, 2010; Nishino and Willden, 2012). A numerical model that aims to examine the power output and environmental impacts of tidal turbine arrays must be able to capture these features.

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