The optimization of j-groove shape in the draft tube of a francis turbine to suppress the draft surge

Suppression of draft surge caused by vortex and cavitation surge in the draft tube is very important to improve the turbine performance when the turbine is operated in the range of partial load condition. In present work, a series of CFD analysis have been conducted in the range of partial load, design condition and over load of a Francis turbine model with a kind of J-Grooves. The pressure contours, circumferential velocity vectors and vortex core regions in the draft tube are compared by the conditions with or without J-Grooves. Study results show that the J-Grooves can suppress the abnormal phenomena to some extents on the condition of maintaining the efficiency. In the second stage, the shape of J-Groove is optimized step by step considering the groove length, depth and width normalized by the diameter of outlet of turbine runner.