Multi-objective optimization design for broadening the high efficiency region of hydrodynamic turbine with forward-curved impeller and energy loss analysis

The energy recovery hydrodynamic turbine is characterized by convenience and high efficiency, has become the core energy conversion device in energy-saving and emission reduction systems in the world. The forward-curved impeller pump as turbine (FCI-PAT) exhibits advantages such as wide high efficiency region and strong operational stability, but its hydraulic design method is still immature. In this study, a multi-objective optimization design for the FCI-PAT is carried out based on numerical simulations and experimental test, aiming to broaden the high efficiency region. The blade inlet setting angle β1, blade outlet setting angle β2, blade wrap angle φ, blade inlet width b1 and blade number z of the forward curved impeller are optimized by combining artificial neural network and intelligent optimization algorithm. The energy loss mechanism in the FCI-PAT is investigated based on the entropy production theory, and the reasons for the performance improvement are analyzed in depth. The research results show that the weighted average hydraulic efficiency of FCI-PAT is increased by 2.06 % after optimization. The hydraulic efficiency of the FCI-PAT increased by 0.95 %, 3.04 % and 1.65 % under 0.8Qd, 1.0Qd and 1.2Qd, respectively. The hydraulic loss in the impeller and draft tube of the optimized model is reduced significantly, with a more uniform distribution of streamlines and a narrowed low-velocity region. The entropy production rate at the suction surface side of the impeller inlet and draft tube inlet of the optimized model is significantly decreased under three conditions, and the reduction is the most significant under 1.0Qd. The inlet and outlet design parameters of the forward-curved impeller have a significant impact on the energy recovery efficiency of FCI-PAT and should be focused on at the design stage.