Modelling tidal stream turbines

Abstract

The transient behaviour of the sea and the rotation of a turbine rotor can result in high asymmetric loadings, which are transmitted to the drive shaft. A turbine mounted on a circular stanchion has been used to highlight the effects of introducing more realistic boundary conditions, over a rotational cycle of the turbine. The consequences on the turbine's performance characteristics and crucial structural loading are shown. The position of the turbine relative to the support structure and its alignment to the flow direction can have significant temporal hydrodynamic and structural effects. Depending on their wavelength, waves can also have a significant effect on the overall design decisions and placement of devices. Thrust loading and bending moments applied to the drive shaft can be of the order of hundreds of kN and kNm, respectively. This leads to the need to not only size the drive shaft and bearings to account for axisymmetric thrust but also consider large asymmetric loads. Knowledge of the flow regime can allow the designers to evaluate material selection for components (i.e. for blades, etc.) and incorporate some deformation capability of the turbine blades to increase the power output and potentially alleviate some of the stress distribution through key structural points, that is, drive shaft, bearing connectors, etc. The resulting data can then be used to estimate component life via fatigue prediction. This chapter includes a multi-physics approach to modelling tidal energy devices and the potential for modelling to inform device condition monitoring.