Turbulence Characteristics Through the Water Column in an Open Channel for Hydrokinetic Turbine Deployment

Flow characteristics in a river or open channel, including mean flow velocities and turbulence intensity profiles, are essential information for the marine and hydrokinetic energy industry in site selection, engineering design, commissioning, and operation phases. Using an acoustic Doppler velocimeter (ADV), a precise velocity measurement from the free surface to the boundary layer region of a rapid current channel is performed for the first time. In this paper, we introduce a novel technique to deploy and control an ADV from the free surface to the boundary layer of a fast-current channel to improve the accuracy of the flow data obtained from traditional techniques such as acoustic Doppler current profiler (ADCP) or single point ADV (e.g., near-surface or near channel bed). The knowledge of true flow characteristics and turbulence properties at different depths in a fast-current river or channel can lead to better performance evaluation, lifetime estimation, and power output prediction. This investigation is conducted at the Canadian Hydro Kinetic Turbine Test Centre (CHTTC) on Winnipeg River. Results indicate that the maximum mean velocity occurs at about 3 m below the free surface, independent of channel depth and mean velocity, and drops by 34 % at 0.8 m above the channel bed, in the boundary layer region. Therefore, flow in this region carries only 29 % of the energy that the flow has in the maximum velocity point. Turbulence intensity has a reversed pattern and increases near the channel bed. The free surface to half depth changes is gradual, both in mean velocity and turbulence intensity. After mid-depth, the mean velocity drops rapidly while the turbulence intensity increases quickly.