Experimental Investigation of the Effect of Passive Flap Configuration on the Performance of the Darrieus Hydrokinetic Turbine at Low TSR

The finite supply of fossil fuels has forced scientists to explore sustainable energy alternatives. One of the alternatives is using a hydrokinetic turbine to generate energy from the water current. Vertical axis hydrokinetic turbine Darrieus type has a range operation in medium to high TSR. In this study, a Darrieus hydrokinetic turbine was tested experimentally in lower TSR to observe the behavior of the attached passive flap on the turbine's blade with different placement configurations, i.e., inner flap, outer flap, and combined flap. The passive flap movements were limited to a maximum opening angle of 45° and 90° for each flap position compared to NACA 0018 (Clean) without a flap. The test was demonstrated inside the racetrack flume under Re 14500. All the tests were recorded using a video camera to give clear information regarding the flap's behavior. The turbine torque was measured using a rope brake dynamometer by gradually adding weights to create resistance between the rope and the turbine's rotation. As a result, the inner flap configuration with a maximum opening angle of 90° positively affects the turbine performance compared to all configurations. Attaching a passive flap outside the blade rotation will reduce the turbine performance. The smaller the opening angle of the outer flap, the higher the turbine performance and vice versa. It indicates that the outer flap for Darrieus hydrokinetic turbine is not recommended. Furthermore, the inner flap improves the operation range in lower TSR than the original NACA 0018.