Experimental investigation of wake and thrust characteristics of a small-scale tidal stream turbine array

Tidal stream turbines (TSTs) are usually organized into an array to extract energy from tidal stream efficiently. A deep understanding of wake structures and thrust characteristics of tidal stream turbine array (TSTA) can contribute to its layout optimization. The wake and thrust characteristics of two arrangement types of TSTAs were experimentally investigated and compared. Influences of the spacing distance between turbines were accordingly analyzed and discussed. Through comparison of velocity distribution between two TSTAs, it was found that the wake deficit area of the turbine array significantly increased with an additional upstream turbine. A larger distance was in need for the downstream turbine to recover its wake velocity to free velocity magnitude. Adding a turbine upstream, reduces the flow velocity difference between the downstream turbines, resulting in a better wake merge. The spacing change between arrays is directly related to the position and range of the array wake merge. Moreover, reducing the lateral spacing could potentially facilitate quicker wake merging, while increasing the longitudinal spacing may result in the wake merge area shifting upstream. Additionally, the monopile support structure was found to significantly decrease velocity magnitude and increase turbulence intensity, particularly in the near wake region.