| A centrifugal pump, especially pumps applied in nuclear powers or naval vessels, often works at off-design conditions due to limitations for operating condition. The hydraulic performance of pump at design condition can be fully guaranteed by means of single-point hydraulic design method, while the hydraulic performance for off-design conditions somehow can not be taken into consideration during the design process. Therefore, the multi-conditions hydraulic design and optimization method is a relatively newly research issue. This method is based on single-condition hydraulic design and can meet performance requirements at off-design conditions. It is of great significance to enhance weighted average efficiency of centrifugal pumps at multi-points, enlarge its high efficiency area and improve the stability of its inner flow field.This research is supported by the national outstanding youth fund (No.50825902) and the special fund project of Jiangsu province for the transformation of scientific and technological achievements (No. BA2010155). Considering multi-conditions hydraulic design and optimization problem, a multi-conditions hydraulic design and optimization method for centrifugal pumps is presented based on theoretical analysis, numerical simulations and experimental study. The main research contents and important conclusions obtained are as followings:1. Energy characteristics computation model of centrifugal pumps for whole flow rate range was given and the model could apply to the whole flow rate scope. By using this model, the multi-conditions hydraulic optimum design of centrifugal pumps can be accomplished. Six centrifugal pumps with different specific speeds were chosen to calculate their hydraulic performance. And calculation results were compared with test. The results show that calculation errors of both efficiency and head are within 5% and can meet the requirements of multi-conditions hydraulic design. In order to improve the accuracy of multi-conditions hydraulic optimum design, a correction method of loss coefficients was proposed. Each loss coefficient of performance calculation model for a centrifugal pump whose specific speed is 92.7 was corrected with the Pointer optimization algorithm. Simultaneously, the comparison between hydraulic performance data and test data had been made for the seven impellers with different blade outlet angle, blade outlet width and blade number. It is showed that all errors are less than 4% and can meet the requirements of multi-conditions hydraulic optimum design. 2. A multi-conditions hydraulic performance optimum design method for centrifugal pumps was proposed. The method used key geometric parameters of single-condition as the initial values, heads at multi-conditions as the constraints condition, and the maximum of weighted average efficiency (or the minimum of weighted average power) at multi-conditions as the objective function. Global optimum algorithm was used to solve the energy performance calculation model and the super-transitive approximation method was applied to fix optimal weight factors of individual objectives. A centrifugal pump with special speed of 129.3 was optimized with the method. The CFD numerical simulations were done for original design and multi-conditions hydraulic optimization design respectively. It can be concluded that weighted average efficiency of optimization at 0.6Qd, 1.0Qd and 1.2Qd has increased by 0.46 percentage points than that of original design.3. Multi-conditions automatic CFD optimization of impeller meridional shape for centrifugal pumps was realized by means of Isight software integrated Pro/E, Gambit and Fluent software. The shroud arc radius R0 and R1, shroud angle T1, hub arc radius R2 and hub angle T2 on the meridional shape were selected as the design variables and the maximum of weighted average hydraulic efficiency at the 0.6Qd, 1.0Qd and 1.2Qd was chosen as the objective function. Data samples were generated by means of Optimal Latin Hypercube Experimental Design Method and optimal weight factors of individual objectives was generated from the super-transitive approximation method. A centrifugal pump with special speed of 84.8 was optimized with this method. The results show that the weighted average hydraulic efficiency at 0.6Qd,1.0Q2d and 1.2Qd increases from 82.68% to 84.10%, which improved 1.42 percentage points.4. Based on the above research results, a multi-conditions hydraulic design and optimization method for centrifugal pumps was developed. A centrifugal pump with guide vanes was designed with the method. The experimental results indicate that head error is 1.95% when flow rate is 19.7m3/h. Head error is 1.06% for flow rate 32.8 m3/h and head error 4.22% for flow rate 45.9 m3/h. And a double blade centrifugal pump was optimized with the method. The experimental results of the double blade centrifugal pump show that efficiency at 0.8Qd has increased by 1.76 percentage points, efficiency at 1.0Qd increased by 1.11 percentage points, and efficiency at 1.2Qd by 1.69 percentage points. And weighted average efficiency of three-conditions optimization has increased by 1.46 percentage points than that of original design.5. PIV technique was applied to measure the flow field of the centrifugal pump with guide vanes at 0.6Qd,0.8Qd, 1.0Qd, 1.2Qd and 1.4Qd. The external trigger synchronization system was made with fiber optic to avoid disturb of electrical signal for frequency converter. Equivalent calibration method was applied to ensure the accuracy of PIV test. Moreover, centrifugal pump PIV velocity process software which was multifunctional was compiled to obtain the relative velocity, axial velocity, dynamic pressure, angular momentum, dimensionless velocity w/u, v/u, vm/u, vu/u, absolute fluid flow angle and relative fluid flow angle. PIV measurement results demonstrate that the flow pattern in the pump is steady from 0.6Qd to 1.4Qd, and there is a low velocity region at blade convexity side of guide vane, but has no any recirculation. In the guide vane passage toward the outlet of annular discharge chamber, velocity values at the outlet area of blade convexity are small, but there is no any apparent vortex.6. To compare with inner flow of double blade centrifugal pump before and after optimization, its inner unsteady flow fields were measured by PIV technology. Research results indicate that the stalls occur in the impeller before and after optimization at 0.2Qd and 0.4Qd while stall areas in the optimized impeller are smaller than that in the original impeller. At 0.6Qd and 0.8Qd, the vortex areas occur in the impeller before and after optimization while vortex areas in the optimized impeller are smaller than that in the original impeller. At 1.0Qd,1.2Qd and 1.4Qd, the optimized impeller had better flow pattern, while there are vortex and recirculation in the original impeller.
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