Prediction and experimental verification of vortex flow in draft tube of Francis turbine based on CFD

The three-dimensional unsteady turbulent flow in the draft tube of a Francis turbine was calculated by using the SIMPLE algorithm with the body-fitted coordinate and tetrahedral grid system with the help of FLUENT software. This calculation was based on the Navier-Stokes equations and LES (large-eddy simulation) model. The flowing situations in the draft tube under three operating conditions of this turbine were successfully calculated. The PIV (particle image velocimetry) was used to measure the distribution of flow field at the draft tube cone section at 4 horizontal sections from the outlet of turbine runner. Specialized image analysis software was used to process the experimental results. Through comparison, the results of numerical simulations were in good coincidence with the experimental results.