Analysis of head losses in a turbine draft tube by means of 3D unsteady simulations

URANS simulations and LES in the draft tube of a bulb turbine are presented with the objective to understand the head losses in this turbine component. Numerical results are compared with experimental velocity measurements. The velocity profiles prediction is slightly better with LES than with URANS simulations but the mesh for LES has to be refined to improve the accuracy of the results. Thanks to a detailed analysis of the energy balance in the draft tube, head losses were located in the central vortex structure and next to the walls.