Tidal energy induced by the gravitation between the earth and moon is the most widespread energy with great development potential by hydraulic machineries. Tip leakage vortex (TLV) has significant influence on the flow pattern and energy performance of hydraulic machineries. In the present work, a C groove method is proposed to suppress the TLV and improve the energy performance of a NACA0009 hydrofoil in tidal energy conversion. The numerical approach with mesh generation and Navior-Stokes equation solution is employed to evaluate the effect of C groove. The geometric and flow parameters including groove width, groove edge rotation, groove position, tip clearance size, and inlet velocity are systematically investigated. The function of the C groove is to suppress the primary TLV by groove jet impingement and weaken the secondary TLV by groove breaking flow, and then improve the flow pattern resulting in a higher energy performance. Results show that the C groove can suppress the vortex area under all conditions, and the maximum decrease of vortex area is 66.55% and 67.94% under tip clearance of 0.2 and 0.4, respectively. The C groove can improve the lift drag ratio of foil under all conditions, and the maximum increase of lift drag ratio is 2.79% and 2.10% under tip clearance of 0.2 and 0.4, respectively. With the C groove, newborn vortexes are induced, which can be classified into three types: newborn groove vortex (NGV) in groove, newborn primary TLV (NPTLV) above suction side downstream groove, and newborn secondary TLV (NSTLV) in tip clearance downstream groove. (C) 2018 Elsevier Ltd. All rights reserved.