Research on design and numerical optimization of bowed-twisted-swept cascade of low aspect ratio hydraulic turbine

Abstract

The bowed-twisted-swept modeling technology of three-dimensional blade has been widely used in the gas impeller machinery and achieved good results. This paper introduces the two-dimensional flow theory and the bowed-twisted-swept modeling ideology into hydraulic turbine design. Simultaneously combined with the popular NSGA-II multi-objective optimization algorithm, a complete set of hydraulic turbine cascade design method was proposed. Taking the last-stage low aspect ratio hydraulic cascade of Ф175 type turbine as an example, the parametric model of this cascade was reconstructed by a high-precision automatic bridge coordinate measuring machine. The multi-objective optimization design of three-dimensional modeling of cascade was completed with the single-stage turbine output torque, efficiency and pressure drop as the objective targets. Finally the influence of the bowed-twisted-swept modeling technology on the hydraulic turbine performance was explored in detail by a professional rotating machinery CFD software. Numerical analysis shows that the twisted blade design achieves a 1.5 times increase in torque and 2 to 4 times increase in pressure diff at same working condition. Moreover, when bowing optimization design and sweeping optimization design are applied on the twisted blade individually, the output torque and the stage efficiency of the hydraulic turbine are respectively improved, and when both two methods are simultaneously applied on the twisted blade, it is beneficial to reduce the pressure drop loss. However, it is noticeable that when the bowed-swept modeling technology used in a straight blade using almost have no effect on the turbine performance.