Unsteady Flow Effects on Surging Hydrokinetic Turbines*

Wave surging and tidal currents are two common factors that contribute to the unsteady flows experienced by hydrokinetic turbines. The effects of these unsteady motions on turbine performance and operation, however, are not fully understood. Theoretical calculations suggest that greater energy conversion efficiencies could be gained by taking advantage of unsteady fluid dynamics. In order to repeatably study unsteady effects on hydrokinetic turbines in a controlled laboratory environment, an axial flow turbine was designed to execute periodic streamwise surging motions in a free surface water tunnel. A control scheme for angular velocity of the rotor was implemented in order to optimize the angle of attack over the varying rotor speeds exhibited throughout the surge. This provides an experimental framework through which these unsteady fluid dynamic effects can be investigated.