Open AccessStabilisation of the swirl exiting a Francis runner far from the best efficiency point
Author(s) -
Romeo Susan-Resiga,
Sebastian Muntean,
Alin Bosioc,
Adrian Stuparu
Publication year - 2021
Publication title -
iop conference series. earth and environmental science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.179
H-Index - 26
eISSN - 1755-1307
pISSN - 1755-1315
DOI - 10.1088/1755-1315/774/1/012113
Subject(s) - shroud , mechanics , vortex , draft tube , turbine , physics , rotor (electric) , rope , flow (mathematics) , cone (formal languages) , momentum (technical analysis) , head (geology) , francis turbine , marine engineering , engineering , geology , aerospace engineering , mechanical engineering , computer science , finance , algorithm , geomorphology , economics
The decelerated swirling flow in the discharge cone of Francis turbines operated at partial discharge, far from the best efficiency point, develops self-induced instabilities featuring a precessing helical vortex (so-called vortex rope) which hinders the stable and safe turbine operation. This is an intrinsic characteristic of the swirl exiting the Francis runner, which at part load has a relatively large residual flux of moment of momentum as well as an imbalanced specific hydraulic energy with an excess near the band. We address in this paper the question of how one should alter this swirling flow in order to mitigate further instabilities in the discharge cone. In doing so, we consider an actuator disk located in the upstream part of the discharge cone that model a runaway runner which alter the hub-to-shroud angular momentum and specific head distributions without altering the turbine operating point. However, such a runaway runner provides a swirl stabilisation further downstream thereby effectively mitigating the vortex rope.