Influence of interaction between the diffuser and rotor on energy harvesting performance of a micro-diffuser-augmented hydrokinetic turbine

Abstract A way to quantified diffuser-rotor interaction is presented for a micro-diffuser-augmented hydrokinetic turbine (MDAHT) base on the actuator disc theory (Jamieson, 2011). The large eddy simulation/Reynolds-averaged Navier–Stokes model (DES) for computational fluid dynamics were employed to simulate for bare turbine, bare diffuser and diffuser-augmented turbine, respectively. The axial induction factor of bare diffuser was obtained via the average speed of the turbine center plane, and that of both bare turbine and diffuser-augmented turbine were obtained based on the computational CP and CT. The result shows that the interaction between the diffuser and rotor are corresponding to equivalent axial induction factor ai and ai+ ad, which is tightly relative to diffuser shape parameters and the operational parameters. Bigger angle of attack and camber of diffusers contributes to higher positive ai and higher negative ai+ ad, and more energy harvesting performance on MDAHT is acquired. Besides, angle of attack and camber of diffuser also affected the variation of the CP and CT curve. The maximum TSR point was shifted to higher TSR position with the increase of angle of attack and camber of diffuser, and the angle of attack has a larger influence on the energy harvesting performance for MDAHT comparing with the camber of diffuser. Moreover, the influences of the tip clearances and diffuser contraction ratios on energy harvesting performance versus TSRs were also investigated.