Double-suction centrifugal pumps form an integral part of power plant systems in maintaining operational stability. However, there has been a common problem of achieving a better cavitation performance over a wider operating range because the traditional approach for impeller design often leads to the design effect not meeting the operational needs at off-design conditions. In addressing the problem, an optimization scheme was designed with the hub and shroud inlet angles of the double-suction impeller to minimize the suction performance at non-design flow conditions. A practical approach that speeds up the cavitation simulation process was applied to solve the experimental design, and a multi-layer feed forward artificial neural network (ANN) was combined with the non-dominated sorting genetic algorithm II to solve the multi-objective problem into three-dimensional (3D) Pareto optimal solutions that meet the optimization objective. At the design point, the suction performance was improved by 6.9%. At non-design flow conditions, the cavitation performance was improved by 3.5% at 1.2Qd overload condition, 4% at 0.8Qd, and 5% at 0.6Qd. Additionally, there was significant reduction in the attached cavity distribution in the impeller and suction domains when the optimized model was compared to the original model at off-design points. Finally, the optimization established a faster method for a three-objective optimization of cavitation performance using ANN and 3D Pareto solutions.

Compared with the traditional reverse multistage pump as hydraulic turbine, hydraulic turbine in turbine mode (T‐type turbine) with low specific speed has higher single‐stage energy head, which can effectively reduce stages and increase the stability when it is used to recycle high residual pressure liquid. Blade number of runner is an important design parameter, which has great influence on the performance of T‐type hydraulic turbine and need to be further studied. Therefore, two‐stage T‐type turbine models with different blade numbers are established through numerical simulation. Then, the accuracy of numerical simulation is verified by test. Finally, the performance and pressure fluctuating characteristics of turbine with different blade numbers are obtained. The results show that: (a) Taking same blade numbers in both stages (traditional design method), the turbine efficiency can be higher with the blade number of primary runner and secondary runner are 14, but resulting the superposition of pulsation in secondary runner; (b) Taking different blade numbers in both stages, respectively, the superposition of pulsation can be effectively avoided, which also leads to the increase in efficiency, and up to 81.169%; (c) The method of using different number of blades in different stages can replace the traditional design method and effectively improve the hydraulic performance of T‐type hydraulic turbine.

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To study the influence of rotational speed on the performance of hydraulic turbine in turbine mode (T-type turbine), the performance of turbine at different rotational speed was predicted through theoretical analysis, based on the Navier-Stokes equation and standard k-ε turbulence model, numerical simulation was used to study the performance of turbine at different rotational speed. The head loss, pressure distribution, turbulence kinetic energy, and unsteady pressure pulsation were also clarified. The results shows that with the increase of rotational speed, the high efficiency area of turbine gradually becomes wider, and there is little difference of the maximum efficiency at different rotational speeds. Under the optimal working condition, the pressure difference between inlet and outlet increase gradually, and turbulent kinetic energy of runner also increase. The inlet circulation increases with the increase of rotational speed, the outlet circulation increases with the increase of speed under small flow conditions, and decreases with the increase of rotational speed under large flow conditions. The study of pressure pulsation shows that the increase of rotating speed can effectively reduce the pressure pulsation in the runner. When the rotating speed is 2100 r/min, the amplitude of pressure pulsation at P7 is 10.39% lower than that at 900 r/min. Considering the hydraulic characteristics and the pulsation characteristics, it is recommended that the hydraulic turbine operates at or above the rated speed as far as possible.