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Flow separation over a hydrofoil affects its hydrodynamic performance and ultimately reduces the power production of a turbine. Therefore, the different flow control methods have been proposed by the researchers to overcome these challenges. In this study, the combined effects of circular trailing edge with dimple have been investigated numerically on NACA S1210 hydrofoil to control the flow separation of the hydrofoil. The results showed that the coupled effects of the dimple and circular trailing edge modification appeared effective compared to baseline hydrofoil at a wide range of angles of attack. Maximum lift coefficient increments are 9 and 12% at an angle of attack of 10° and 12°, respectively, for circular trailing edge hydrofoil. The maximum increase of glide ratio for the coupled effect (circular trailing edge with outward dimple) is approximately 114% at an angle of attack of 12°. The outcome will be advantageous to design a proper blade profile for horizontal axis current turbines.

The annual power output of a current turbine is affected by flow separation followed by the stall condition in an environment of varying current speed. Flow separation appears as the fluid in the boundary layer over the blade surface loses its kinetic energy. Delaying this separation process is essential to extract more power throughout the year considering the variation in the current speed. Several active and passive means are available in the literature today to achieve a delay in the flow separation process. Inserting tubes in an aero/hydrofoil at a constant spacing, connecting the fluid near the leading edge and a downstream location on the suction side is a novel approach that has been numerically investigated here. The baseline profile chosen here is S1210, which is used in the current turbine blades. The hydrodynamic performance of the profile with tubes has been compared with the baseline profile in terms of the force coefficients, lift to drag ratio, and stall angle. The maximum lift has been noticed to be increased by 18% and the stall is delayed by 2 deg (from 10 deg to 12 deg). The maximum lift to drag ratio is increased by 130% at 12 deg (beyond the stall of the baseline profile). The results show that the insertion of tubes can make the existing profile more efficient for the stated application.