Experimental analysis of the swirling flow in a Francis turbine draft tube: Focus on radial velocity component determination

The swirling flow exiting the runner is complex and highly turbulent. The radial velocity is rarely measured because a quite complicated measurement setup is needed. However, this velocity component is greatly needed in order to properly initialize the numerical simulations, and its influence is important in spite of its small magnitude. Velocity measurements downstream of the runner include radial component made at CREMHyG (Grenoble) by LDV, and PIV techniques are presented. An analytical formulation for this velocity component based on the formulation for the conical diffuser and on the three vortices structure is proposed and compared with measurements.