Characterization of no-load conditions for a high head Francis turbine based on the swirl level

Abstract

This paper compares the average flow topology in the draft tube cone of a high head Francis turbine operated at full-gate opening no-load (runaway) and speed-no-load (SNL). The comparison is based on the swirl level in the turbine quantified with the angular momentum parameter (RCu11) and the Swirl number. This study shows that RCu11 only depends on the flow angle at the guide vane outlet, the distributor height and the runner outlet diameter. The Swirl number has strong limitations in characterizing the flow at runaway and SNL and is unsuitable for no-load conditions.