Numerical Forcast And Research On The Design Method For Centrifugal Pumps With Splitter Blades

The low-specific speed centrifugal pump has been used widely in most industrial fields, in order to improve its hydraulic performance and control the inner flow condition, splitter blades were added between two long blades. The former researches show that, the adding of splitter blades does improve the performance of centrifugal pumps. Based on the Foundation of National College Doctoral Program, numerical simulation and performance tests were adopted to study the centrifugal pumps with splitter blades, to explore the relation among the design of splitter blades, the pump inner flow condition and pump performance, and to improve the design method for the centrifugal pumps with splitter blades. The innovative achievements and important conclusions obtained are as followings:(1) The research states of inner flow tests and numerical simulations for centrifugal pumps were reviewed briefly, the principle of performance improvement and efficiency increase for adding splitter blades were discussed, and the research state for splitter blades was analyzed also; meanwhile, the theoretical characteristics, inner flow laws and the viscous losses for centrifugal pumps were introduced comprehensively.(2) The former research achievements in our work group were summarized, which including the impacts of splitter blades to centrifugal pumps performance from the orthogonal tests, and the comparison results between CFD(Computational Fluid Dynamics) and PIV(Particle Image Velocimetry). On these bases, several schemes were designed with different splitter blades inlet diameters and the bias angle in peripheral direction, and the simulations of inner flow in impeller were done, to explore the principle of improving the flow conditions. And the variables of turbulence kinetic energy and blade loading were adopted here for the first time to analysis the relation between the adding of splitter blades and impeller work applied, and to find the principle of improving the "jet-wake" structure. And by the analysis the velocity of the multi-sections of one flow passage, the distribution of velocity and flow rate in two sub-passages were visualized.(3) Blade number was adopted in design, and several improved design schemes were given, and the whole flow field simulations, which including the internal space between the pump volute and impeller, were carried out for the first time. And one of the schemes was picked out to analysis the calculation accuracy, which based on different turbulent models, grid sizes, and iterative residuals, to minimize the human error and provide accurate and stable calculation results for all the schemes. The performance curves for all schemes were forecasted, and the effects of splitter blades were concluded, the curve of H -Q is more flat, the curve ofη-Q move to the larger flow rate, and the district with high efficient broadened, the curve of P-Q is steeper.(4) By comparing the total moments on the surface of impeller blades, and combine the distribution law of turbulence kinetic energy, the principle of "the applied moment on splitter blades should be positive" was presented for the first time, to define the upper limits of the splitter blades inlet diameter; and based on the empirical methods, the calculation formula for the splitter blades inlet diameter was established.(5) The viscous losses on the inner and outer surface of impeller shroud and hub and the disc friction loss, under different operation flow rates, were forecast through the simulation analysis; and by comparing the value on the design point with the results from empirical calculation, they are good consistent with each other; and it is found out that the distribution law of disc friction loss with the varying of flow rate, the loss on the 1.0Q_d point take about 15% of the whole shaft power, while the loss on the 0.4Q_d point take more than 30%.(6) The L₉ (3⁴) orthogonal experiments was adopted, and the tested impellers were manufactured with the craft of FDM(Fused Deposition Modeling). By the orthogonal experiments, the primary and secondary sequence of the design parameters of splitter blades were obtained, and the design principles of them were also presented. In order to verify the former simulation results, several impellers in Chapter 4 were manufactured and performance tests were done; the comparison show that, the distribution law of the performance curves are coordinate well, but the data from simulated head is higher by about 5%, and the simulated efficincy higher by about 10%, which satisfy the engineering requirements.(7) The non-overload characteristics of the centrifugal pumps with splitter blades were analyzed for the first time. For the same impeller designed in the former chapter, a volute, which is the same type and has better shaft power performance, replace the original one, and the whole flow field simulation was done. The study result shows that, the modification of throat area can only change the position of the highest efficiency, while the curve shape is not varied. For another centrifugal pump with splitter blades and has the requirements of high-efficiency and non-overload, three volute schemes with different throat area were designed and numerical simulation and performance tests were done, the impact of the volute throat area on the non-overload requirement of centrifugal pumps with splitter blades, and the improvement of shaft power characteristics were analyzed, and a conclusion was drawn that it is difficult to control the shaft power characteristics through the single change of the volute throat area.(8) The design methods for the geometry parameters of the splitter blades in the low-specific centrifugal pumps were summarized. And for the impeller adding splitter blades, the coefficient of flow rate in the flow-enlarged method was revised based on the tests results analysis and several geometry parameters of impeller was discussed. And a recommendation was given, when design a centrifugal pump with splitter blades, the non-overload characteristic should be considered, especially the blade outlet angleβ₂ should select a smaller one in the recommended value span, and the volute throat area is another key factor, which should be in the span of 0.73～1.90.