Effect of guide vane profile on the hydraulic performance of moderate low-specific-speed Francis turbine

The matching between the guide vane (GV) and runner is essential for the stable and efficient operation of hydraulic turbines. To investigate the compatibility between GV and runner, we have conducted the numerical calculations of a moderate low-specific-speed Francis turbine at 25 operating points within the operating range of 130–190 m head and 3–19° GV outflow angle. The energy characteristics, flow field characteristics, and static pressure variation of turbines with different GV profile types have been comparatively analyzed. The results show that moderate low-specific-speed Francis turbines with symmetrical and negative curvature GV demonstrate higher efficiency under medium to high head, 55–100 % rated output operating conditions. Under small opening and medium head conditions, the static pressure in the blade leading edge is smaller, and the low-pressure area is larger for the Francis turbine with positive curvature GV. When the GV opening increases, the relationship between the comparative values of static-pressure and low-pressure areas reverses. The turbine with positive curvature GV is more favorable for increasing static-pressure and narrow low-pressure areas, which can reduce the cavitation damage. Our study provides guidelines to optimize the design of GVs and runner for hydraulic turbines.