| This thesis is supported by the National Key Research and Development Program(2016YFB0200901).It is difficult to improve the hydraulic and acoustic performance of centrifugal pump synergistically from the perspective of traditional design.It is a better solution to solve this problem by using the bionic principle to extract the special biological prototype features in the natural world for drag reduction and noise reduction.Bionic structures are relatively small in size.It often requires hundreds of millions or even billions of units of large-scale grid to study their mechanism by using high-precision numerical methods such as direct numerical simulation,separated eddy simulation or large eddy simulation.Although the rapid development of high-performance supercomputers in China has provided enough hardware support for this purpose,the general centrifugal pump large-scale meshing software is relatively scarce.Therefore,the study of large-scale parallel mesh generation algorithm for distributed supercomputers is of great significance for achieving high-precision numerical simulation of bionic centrifugal pumps and establishing the relationship between key flow parameters and drag reduction and noise reduction.In this thesis,the parallel mesh generation,flow field and sound field characteristics of bionic vane centrifugal pump and multi-objective collaborative optimization of centrifugal pump are studied in depth by combining theoretical mechanism analysis,high-precision numerical simulation and test.The aim is to propose a large-scale parallel mesh generation algorithm to grasp the mechanism of drag reduction and noise reduction of bionic blades of centrifugal pumps,and to achieve the coordinated improvement of hydraulic and acoustic performance of centrifugal pumps.The main work and research results are as follows:1.The basic concepts and ideas of parallel mesh generation are expounded.The application and analysis of drag reduction and noise reduction using bionic ideas are summarized.The ideas and methods of multi-objective optimization of centrifugal pumps are summarized.2.Based on the domain decomposition method,a large-scale parallel mesh generation algorithm for high performance computers is proposed.The algorithm can effectively adapt to the complex surface of centrifugal pump water body and ensure the consistency of interface meshes.The algorithm is numerically tested on Tianhe 2 supercomputer platform,and large-scale parallel network partition and LES numerical calculation of centrifugal pumps are carried out.The results show that: the grid generated by this algorithm is of high quality and can inherit the guarantees of the original serial grid algorithm for grid quality;The parallel mesh generation algorithm proposed in this thesis can effectively break through the limitation of existing serial programs on mesh size and generate 108-order mesh elements in 5 minutes;When the number of parallel cores is not more than 12 cores,the parallel efficiency is more than 75.92%;The results of the large-scale grid can more accurately capture the velocity distribution of the flow field inside the pump,revealing the unstable flow structures such as vortices and twin vortices closer to the PIV results.3.In order to grasp the relationship between the key parameters of internal flow and the effect of drag and noise reduction,the non-smooth structure features of the mantis body surface were extracted and arranged in the outlet area of the centrifugal pump blade working face.Large eddy simulation of internal flow field is carried out based on large scale parallel grids.The noise distribution in centrifugal pump field is simulated based on Proudman semi-empirical model method and direct boundary element method.The relationship between the average shear stress rate,drag reduction rate,increase efficiency and total sound pressure level noise reduction rate of internal flow key parameters is studied,and the mechanism of drag reduction and noise reduction of bionic blades is analyzed.The study found that: The bionic pit structure can effectively increase the thickness of the low-speed boundary layer near the wall and reduce the Reynolds stress on the wall,thus effectively reduce the resistance on the wall and improve the hydraulic efficiency of the centrifugal pump;The mechanism of "reverse vortex" drag reduction at the bionic pit is found and put forward,so the pits arranged on the bionic blade play the role of "micro rolling bearing" and reduce the friction of fluid flow near the blade wall;The bionic blade has certain uniformity for the optimization of the sound field and the flow field of the centrifugal pump.The noise reduction rate of the total sound pressure level of the noise is basically consistent with the change trend of the drag reduction rate,the increase efficiency and the average shear stress change rate in the flow field;The wall average shear stress in the internal flow parameter has the greatest contribution to the drag reduction,synergy and noise reduction effects.The effect of the drag reduction can be predicted and judged by the variation of the average wall shear stress.4.A multi-objective optimization method for hydraulic and acoustic performance of centrifugal pumps based on experimental design and response surface was established.Taking three parameters of bionic pit diameter d,axial pitch e and radial pitch f as design variables,and taking the highest hydraulic efficiency of centrifugal pump and the reduction of total sound pressure level as response objectives,a multiple regression response surface model between design variables and multi-objective functions was constructed;The interaction between multi-objective parameters is analyzed,and the optimal parameter combination for the collaborative optimization of hydraulic performance and noise is determined;method based on response surface method has high prediction accuracy,which can significantly improve the hydraulic and acoustic performance of centrifugal pumps.The optimized external characteristic curve makes the maximum efficiency point shift to the direction of large flow rate and effectively widens the high efficiency working area of centrifugal pump.Under rated conditions,the drag reduction rate can reach 2.13%,the hydraulic efficiency of centrifugal pumps can be increased by 3.03 percentage points,the relative change rate of efficiency can reach 4.21%,the total sound pressure level can be reduced by 4.96 dB,and the noise reduction rate can reach 3.01%. |
