The marine environment offers many challenges for accurate performance modelling. Capturing the spatial and temporal variation in the marine flow is vital for the prediction of both performance and loading on tidal stream turbines.
Conventional blade element and momentum theory (BEMT) assumes a uniform flow velocity normal to the horizontal axis rotor. Alterations have been made to allow for non-uniform, three-dimensional flows. This work involved a system to map the rotor blades in a three dimensional global space and resolve flows into blade relative, local vectors. This also allows for yawing, teeter and rotation of the blade system.
An open source code has been employed to model the velocities and accelerations of water due to waves. The BEMT analysis is modified to use this varying velocity regime to calculate rotor performance. However, the acceleration of the fluid is also taken into account in a post-processing routine.
Tidal flow has been modelled as a power law boundary layer. This gives a variation in flow velocity with water depth. The flow velocities of wave action and tide are combined to give a flow velocity field, which may be used in BEMT.
The implementation of these approaches is shown and the results discussed.