Draft Tube calculations

Steady state computations are routinely used by design engineers to evaluate and compare losses in hydraulic components. In the case of the draft tube diffuser, however, experiments have shown that while a number of operating conditions can adequately be evaluated using steady state computations, some operating conditions require unsteady simulations to accurately evaluate losses. This paper presents a study that assesses the predictive combination of steady and unsteady RANS numerical computations to predict draft tube losses over the complete range of operation of a Francis turbine. For the prediction of the draft tube performance, a systematic methodology has been propose different turbulence models for steady and unsteady computations. The proposed methodology consists to average global performance indicators of steady flow computations such as the pressure recovery factor over an ade those obtained using unsteady flow computations. OpenFOAM flow solver, through comparison with experimental results obtained on the FLINDT model draft tube. Previous work using CFX and OpenFOAM can be found in [1].