This research aimed to systematically maximize hydraulic efficiency and suction specific speed for mixed-flow pump using a commercial CFD packages and optimization tool. First, mixed-flow pump was initially designed according to the traditional design method, and then the blade shape was re-designed by focusing on the hydraulic efficiency. Second, the efficiency-oriented optimum design was selected as the reference model. The objective was to improve the suction specific speed under the specific condition of the mixed-flow pump through the multi-objective optimization technique. The incidence angles and meridional plane were optimized through a systematic optimization process, namely, central composite method and response surface approximation. The optimization results indicated that the suction specific speed values of the reference and optimum model were 88.13 and 289.65, respectively. Furthermore, the hydraulic efficiency was kept within ± 1% compared to the reference model as the constraint condition. The hydraulic efficiency of the reference and optimum model were 91.44% and 90.40%, respectively. The reasons for the improved efficiency and suction performance were investigated through internal flow field analysis. Finally, the reliability of the optimization was demonstrated by comparing the numerical and experimental results.

In this article, design optimization was carried out to improve the suction performance and efficiency of a mixed-flow pump impeller. Commercial computational fluid dynamics code and a response surface method were used in the optimization to design a mixed-flow pump impeller. When it comes to a mixed-flow pump, the two main research objectives namely efficiency and suction performance tend to contradict. It is very important that the design technology improves the suction performance while maintaining high efficiency. Meridional plane and vane plane development variables were defined in the design of the impeller. The meridional plane expresses the shapes and sizes of the blades, while the vane plane development describes the impeller inlet and outlet angles as well as the blade angle distribution. The blade angle distribution of the impeller was designed using the traditional method by which inlet and outlet angles are connected smoothly. The surface response method was applied to the design variables of the impeller inlet part in this design optimization because they influence the performance of the mixed-flow pump. Objective functions were set to satisfy the total head at the design flow rate as well as to improve efficiency and suction performance. Design variables of the impeller inlet part of the mixed-flow pump and the changes in performance were analyzed in order to produce the optimal shape. The performance of the optimally designed shape was verified by numerical analysis, and the reliability of the test result was checked by comparative analysis against the reference model.

The blade leading edge is a design variable that can affect the local flow patterns and pressure peaks, implying a direct effect on the cavitation performance. This study was conducted to analyze the effect of the blade leading edge shape on the cavitation and noncavitation states. A total of four sets, including the square shape, were selected under the definition of ellipse ratio, and the main focus was on the cavitation state rather than the noncavitation state. In the noncavitation state, the square set denoted a remarkable negative influence, while the other three sets obtained almost the same performance despite different ellipse ratios. In the cavitation state, the square set obtained a relatively low net positive suction head required, related to the inlet flow pattern with the cloud cavity. The other three sets contained the sheet cavity, and their suction performance tended to improve as the cavity blockage decreased. As a parallel focus, an in-depth analysis of cavitation surge and pressure gain was presented with the head drop slope for the other three ellipse sets. The numerical results included the off-design flow rate points and were validated through an experimental test.

An axial fan in the general industry needs to secure stable characteristics in a wide operating range through an antistalling process, concerning its high demands, energy consumption, safety, and lifetime. As a “simple” and “original” method to control the stall of an axial fan, two-dimensional plates so-named anti-stall fin (ASF) were attached inside the casing and toward the shaft. The sensitivity analysis for design variables was conducted through the $2k$ full factorial design method, and the optimization was performed using the response surface method (RSM). In the case of an axial fan without the ASF, the backflow gradually increased in the spanwise direction toward the hub and the streamwise direction to the inlet passage (upstream), as the flowrate decreased, and the rotating stall was developed through the quickening-growing-setting period. However, an ASF-attached axial fan stably recovered performance degradation in the stalling flow rates and allowed to form a negative slope to 0.5 $Φd$⁠. This study was mainly based on numerical simulations, while the performance before/after application of the ASF was validated through experimental tests.