Assessment of the distributor layout influence on the vortical flow within the hydraulic turbine

Abstract

The study presents analysis of conditions for the onset of vortices in the simplified geometry of the turbine domain. The simplified geometry, used for this analysis, is based on the physical model of the bladeless swirl generator developed by the research group from Brno University of Technology. This swirl generator was previously used for several studies of the spiral vortex structures generated in the diffuser part. In original geometry there are no guide vanes or other driving geometry features, thus the mixing mechanism is realized randomly, is strongly time-dependent and its behavior is linked to the swirl ratio between the axial and tangential inflows. From previous studies, the appearance of vortical structures with columnar-like shape was identified. Thus, the main aim for the current study is to assess the influence of distributor blade cascade on the onset and behavior of such vortical structures which resembles the ones observed in hydraulic turbines at low load conditions. For selected swirl ratio the distributor blades are designed specifically to influence flow with minimal effect. The distributor layouts with different number of blades are tested. The dynamics of vortices, their spatial shape and extend are examined through several post-processing tools. The results are mainly based on the CFD simulation employing a hybrid RANS+LES turbulence model.