Abstract: Tidal bidirectional tubular turbines, unlike conventional units, need to consider both forward and reverse flow conditions. To balance and improve their performance under these two operating modes, this study investigates the effect of the position and number of different rear guide vanes on the performance and internal flow characteristics, using ANSYS CFX for flow simulations and taking a real project unit as a test case. The results show the position and number of these vanes have a great impact on the generating unit in reverse mode. The overall performance is better at a vane position coefficient of 0.5 and a vane number of eight. In forward mode, with the increase in the vane number, head loss decreases in draft tube but increases in rear vane channels; in reverse mode, the runner has a decreasing head loss and a gradually increasing efficiency. The results are useful for optimization design of the key flow components of tidal bidirectional tubular turbines.

Key words: bidirectional tubular turbine, rear guide vane, CFD, hydraulic loss, design optimization