Active vortex control downstream the turbine runner in the Francis hydro turbine model

This paper presents the development of active control methods for vortex phenomena in hydro turbines. The flow pattern downstream of a simplified turbine runner was studied under conditions typical of a hydro turbine operating at partial load, which are prone to generating large-scale vortex structures and inducing powerful pressure pulsations. Active control was achieved through the injection of additional air jets into the center of the runner cone. The results of experiments covering velocity distributions, velocity pulsations, and pressure pulsations following the injection of jets are presented. Control jets, regardless of their orientation, successfully suppress pressure pulsations. However, jets oriented radially provide the most effective suppression of vortices and reduce the total flow swirl in the draft tube. The pattern of jet supply directly affects the formation of a recirculation zone downstream of the runner. Experimental data on optimal injection align with previous theoretical estimates based on flow linear stability analysis.