Output of a tidal farm in yawed flow and varying turbulence using GAD-CFD

Tidal stream turbine arrays will be subject to a range of flow conditions throughout the tidal cycle and it is important for developers to have an understanding of the impact of these on array performance when planning site design. A generalised actuator disk-computational fluid dynamics (GAD-CFD) model is used to conduct simulations on a three and fourteen turbine array arranged in two different configurations. Firstly, simulations of both arrays are conducted in straight flow conditions to understand the hydrodynamics around devices and evaluate their performance. Performance predictions for the three turbine array in straight flow conditions are in close agreement with previous studies. In the fourteen turbine array, wake recovery to freestream conditions was better in the modified formation compared to the regular formation and the total power output was increased by over 10%. The influence of yaw angle and upstream TI (turbulence intensity) on both array performance was also studied. Strong sensitivity of overall farm power and thrust was found to exist in small variations in yaw angle. However, the overall wake structures were similar irrespective of the yaw angle. Finally, simulations of different turbulence intensities showed rapid decay shortly downstream of the inlet. In all arrays, turbulence intensity had little effect on the thrust and power of the upstream set of devices for the considered TI range but greatly influenced the individual downstream devices.