Wake Analysis of a Freewheeling Vertical Axis Hydrokinetic Turbine in Aquatic Environment

Hydrokinetic turbines are a promising form of renewable energy, offering sustainable power generation. The aim of this study is to investigate the behavior of such turbines under real-world conditions, giving insights on flow and turbulence patterns in aquatic environments. Continuous field velocity measurements were performed to examine the behavior and impact of a 25 kW vertical axis hydrokinetic turbine (VAHT) under freewheeling conditions. Flow velocities were measured using acoustic Doppler current profiler (ADCP) and acoustic Doppler velocimeter (ADV) probes. Numerous measurements were taken at different distances behind the turbine, ranging from 1 turbine diameter up to 17 turbine diameters. The focal objective was to investigate turbulence intensity levels at various depths and distances behind the turbine. Results showed that turbulence was most intense in the vicinity of the turbine, peaking at the turbine centerline with 83.98% for the first test and 119% for the second test with ADCP, and 40.82% for the first test and 54.64% for the second test with ADV. Turbulence intensity gradually decreased as the distance behind the turbine increased. Data from both ADCP and ADV were used to further verify the results and compare the findings. Combining the insights from both measurement methods gave a detailed understanding of the flow and turbulence characteristics behind the vertical-axis turbine.