An efficient computational framework for hydrofoil characterisation and tidal turbine design

Blade element momentum (BEM) modelling offers a computationally inexpensive means of analysing turbine performance. Lift and drag coefficient data-sets specific to the operating conditions of the turbine must be input into a BEM model. However, such data is not typically available over the wide range of Reynolds number (Re) and angle of attack (α) encountered by vertical axis turbines. This paper presents a computational fluid dynamics (CFD) approach, based on transitional flow turbulence modelling, to determine lift and drag coefficients for a symmetric hydrofoil. Results are validated against published experimental data for a wide range of α and Re. It is demonstrated that BEM models provide improved predictions of vertical axis turbine performance when CFD generated lift and drag coefficients are used as input, rather than coefficients generated by the widely used panel-method. The combined CFD-based BEM methodology achieves a similar level of accuracy to a full CFD turbine model while providing a significant reduction in computational cost. The modelling approach and hydrofoil data-set developed in this study can be directly utilised for the design and optimisation of next-generation non-straight bladed vertical axis turbine designs which operate over a wide range of α and Re.