Design And Performance Study Of Micro Hydraulic Turbine Used In The Water Supply System Of High-rise Buildings

In the water supply system(WSS)of high-rise buildings,pressure reducing valves(PRVs)are often used to reduce the inlet pressure of the system in order to minimize leakage and damage to the water supply facilities.However,this water pressure control method results in a large waste of energy.To improve the energy utilization efficiency of the WSS,a micro hydraulic turbine was developed to replace the PRV for reasonable control of water pressure in the pipeline and recovery of excess hydro energy.Based on the analysis of the existing research and the working characteristics of different types of hydraulic turbines,the Francis turbine was selected for the research.Through the combination of theoretical design,numerical simulation,and experimental testing,the application feasibility of the micro Francis turbine was investigated,and the structure design and parameter optimization of the developed micro Francis turbine were systematically carried out.The main contents and conclusions are as follows:(1)According to the two-dimensional design methodology,the runner structure design was conducted,and a prototype was manufactured and tested after the optimization of blade outlet angle and blade shape by the numerical simulation method.Subsequently,the effect of runner inlet width on the performance of the micro Francis turbine was studied by experimental testing.The experimental results show that the micro Francis turbine can effectively control water pressure in the pipeline with a certain energy conversion efficiency under the design flow rate.However,the water head of the turbine fluctuates significantly with the flow rate under offdesign conditions,so a control scheme was designed to ensure the expected pressure level in the pipeline.In addition,the research on the effect of runner inlet width shows that ideal values of runner structure parameters can be obtained through the adopted two-dimensional design methodology.(2)The initial volute was designed based on the equal circumferential average velocity method,and the effects of different volute structures and design methods on the turbine performance were studied systematically by the numerical simulation method.The results show that the volute design with a circular cross-section and equal circumferential average velocity method is beneficial to improving the turbine performance.Among the volute outlet width,inlet height,and inlet diameter,the outlet width has a significant effect on the turbine efficiency,while the inlet height has a significant impact on the water head.The optimized volute outlet width is 6.25 mm,the inlet height is 130 mm,and the inlet diameter is 30 mm.In addition,among the shape parameters of the tongue,a larger tilt angle will lead to a lower water head and output power,while a larger stretch length often corresponds to a higher water head,higher output power,and lower efficiency.The optimized tilt angle is 12°,and the stretch length is 4mm.(3)The surrogate model method was used to optimize the shape of the draft tube.The correlation between different design variables and hydraulic efficiency was analyzed,and the prediction accuracy of the different models established using the standard response surface function,Kriging function,and radial basis function,respectively,was compared.Finally,the optimized result was obtained using the sequential quadratic programming algorithm.Compared with the pre-optimization,the shape optimization of the draft tube resulted in a0.79 m reduction in water head and a 1.75% increase in the hydraulic efficiency of the turbine under the design flow rate.(4)Based on the optimized result,the manufacture and performance testing of the micro Francis turbine were carried out.Compared with the initial prototype,the efficiency of the optimized turbine increases 6.5%,the output power is relatively increased by 50.4% under the design flow rate,and the work capacity of the optimized turbine under the off-design flow rate is also significantly improved.In addition,there is no obvious change in the water head of the turbine before and after optimization under the design flow rate,but the water pressure control ability of the optimized turbine under the off-design flow rate is improved.