Comparison of the effects of leakage flow from guide vanes of different hydrofoils using alternative clearance gap approach

Sediments flowing along with water through guide vanes induces abrasive and erosive wear in the GV surface. The effect of these wears differs with the shape of GV profiles. This study presents an alternative clearance gap method to compare the effects of clearance gap (CG) in the GV of Francis turbine with different hydrofoils. Numerical prediction of the performance of Francis turbine with symmetrical and asymmetrical hydrofoils is studied with the CG of 0 mm, 2 mm, and 4 mm thickness. Increase in the size of the gap deteriorates the performance of the runner. In case of asymmetrical GV profile, the effects in the runner is found to be less than the symmetrical profile. It is due to lesser pressure difference between the adjacent sides of the GV profile. With the alternative clearance gap approach, it distinguishes the effect of CG and the pressure pulsation due to rotor-stator interaction for a single numerical model.