The Research On Performance And Inner Flow Of Compound Impeller Of Super-low-specific-speed High Speed Centrifugal Pumps

With the rapid development of most industrial fields such as petrochemical industry, metallurgy and electric power, aviation and aerospace industry, the super-low-specific-speed high speed centrifugal pump gradually develop to the direction of high-speed and high-power. And with diversification of medium transferred by it, especially to transport low-temperature vaporization of liquefied gas and other application areas continues to expand, the centrifugal pump that is high water-head and little discharge, is widely applied. Whether it is designed according to the velocity coefficient method and model conversion method which are based on the traditional similarity theory and the unary theory, than there has some limitations in the design of ultra-low-specific-speed centrifugal pump and restrictions on its own performance and working environment, its efficiency, reliability and stability have further improvement.The CFD numerical simulation are adopted to study internal flow pattern of different impeller types of GS25 super-low-specific speed centrifugal pumps with short blades under the operating point conditions and non-operating points, the whole three-dimensional turbulent flow fields of centrifugal pumps with long and short blades are analyzed, to get the best designing scheme of short blades and find the laws of internal flow and performance of the super-low-specific speed centrifugal pumps with short blades. The main work and achievements are as follows:1. Based on the traditional unary theory for designing and combined with the basic geometric parameters, the complex impeller of the GS25 super-low-specific-speed centrifugal pump are designed by increasing discharge coefficient and the velocity modulus. The initial scheme of the GS25 super-low-specific speed centrifugal pumps had been designed.2. Based on the statistics and orthogonal theory and combined with the four main factors influencing the design of short-blade of complex impeller which contains the number of short-blade, the radial inlet position, the bias angle in peripheral direction and the deflection angle,16 different types of complex impellers with different combinational form of short-blades have been designed. By range analysis of numerical simulation of theL16(44) orthogonal designing scheme, the primary and secondary sequence affecting pump head and efficiency of the four main factors were obtained respectively, and the design principles of them were also presented. Finally, the best design scheme of short-blade was given.3. A three-dimensional solid formation of the blade in spatial cylindrical coordinate system was presented by using Pro/E-based on software for the blade of complex impeller of the GS25 super-low-specific-speed centrifugal pump. The two-dimensional hydraulic model has been transformed into spatial coordinates in this method, and to achieve blade modification by adjusting the coordinates. Compared with the traditional method, this method does not require the various flow line amendments, and it is simple and accurate for blade modification, and laying a reliable basis for improving CFD and performance prediction of inner flow of the centrifugal pump.4. In this paper, the numerical simulation calculation was based on the continuity equation and Reynolds-average Navier-Stokes equation. The control equation was solved by using standard k-εturbulence model and SIMPLEC algorithm. The three-dimensional turbulent flow fields in the ordinary conventional impeller with five blades and the orthogonal design of complex impeller with five blades and five short-blades were analyzed respectively in different working operations, which are 0.5Q,0.8Q,1.0Q,1.2Q,1.5Q.The distribution of velocity and pressure of tow impellers in design operation were emphatically analyzed and compared.Main innovations in this research work:1. The optimization orthogonal design of complex impeller with long and short blades based on the statistics and orthogonal theory were presented, and the best scheme of complex impeller were given.2. A three-dimensional solid formation of the long and short-blade in spatial cylindrical coordinate system was presented. It is solve that the computation for planar profile modification is time-consuming and the operation complex and so on.Due to the limits of time and conditions and my lack of experience, there are a lot of works not done well. It is not satisfied that the Hydraulic model of GS25 super-low-specific-speed high speed centrifugal pump in this paper, and technical performance indicators are not enough advanced too. There has further room for further study.