Performance optimization of axial-flow hydraulic turbine using artificial bee colony (ABC) algorithm

This paper presents the numerical optimization of axial-flow hydraulic turbine performance. The turbine was designed to operate at a net head of 0.9 meters, a rotational speed of 500 rpm, and maximum flow rates are 0.12 m³/s. The initial turbine design was optimized by using shock-free inflow criterion to minimize the hydrofoil losses at the turbine cascades. Potential flow of the hydrofoil was analyzed using surface vorticity model with modified coupling coefficient to deal with turbomachinery blade cascades. The ABC algorithm was used to arrange the geometry of guide vane's and runner blade's cascades to meet the shock-free inflow criterion. In the present study, the cascade geometry optimization of the axial-flow hydraulic turbine is divided into two main steps. Firstly, cascade at each section of guide vane was optimized by arranging two design variables, i.e. stagger angle and chamber line of the hydrodynamic profile. Secondly, cascade at each section of runner blade was optimized by arranging one design variable, i.e., stagger angle. Both steps have the same objective function that minimizes the difference between the design of inlet flow angles and shock-free inflow angles. The optimization results showed that the ABC algorithm performed very well, the average of best values at each section was an order of magnitude of -14. The performance of turbines was predicted using computational fluid dynamics (CFD) approach based on finite volume method. The numerical results showed that the optimization of two-dimensional cascades geometries by using shock-free inflow criterion successfully improved the performance of initial design of axial-flow hydraulic turbine.