Effect of blade perforation on Francis hydro-turbine cavitation characteristics

摘要

A new approach, blade perforation, is presented to prevent flow cavitation on the blades' suction side in Francis hydro-turbines. The blades are perforated at the sites of cavitation so that the pressure and suction sides are connected by the through-hole to increase the pressure at the suction side. The detailed characteristics of flow, performance, cavitation in the runner and vortex rope, and pressure fluctuations in the draft tube of the perforated and unperforated turbines are investigated numerically and experimentally. Under the conditions of this study, the blade perforations do not change the energy extraction performance and the critical cavitation number, but do influence the flow characteristics and ameliorate the turbine instability problems: change the shape of vortex rope; eliminate high-frequency bubbles and reduce the amplitude of pressure fluctuations in the draft tube. This indicates that blade perforation can be used as a novel method to improve the stability of hydro-turbines.