Study On Transient Start-up Characteristics Of An In-pipe Spherical Hydraulic Turbine

The in-pipe Spherical hydraulic turbine is a new type of liquid residual pressure energy recovery device,in urban water supply networks and other fields have a broad application prospects,because the pipeline cross-section for the circular cross-section,Spherical type hydraulic turbine effective sweep area is larger,with higher hydraulic performance.Currently the technology has been successfully applied in the water supply network of Riverside and Portland in the United States,such as the application of the device in China will meet the urgent need for the development of urban intelligent water services.And Spherical type hydraulic turbine for vertical axis installation,its generator module installation is simple and convenient,and operation is not affected by the direction of the incoming flow,no adjustment device.However,in practice,due to the uncertainty of the water flow,the hydraulic turbine may repeatedly go through the start-stop process,and if the hydraulic turbine has poor starting performance,the addition of auxiliary start-stop equipment will make the generator module complex.The study of this problem has important engineering application value,so this topic will be based on SDOF solver to investigate the transient start-up characteristics of the ducted Spherical hydro turbine,which are as follows:(1)The object of the study was a pipeline-type Spherical hydraulic turbine with DN50,a chord length to diameter ratio of 0.211,and 5 blade count.A visualization experiment was conducted to investigate the critical start-up characteristics.The results showed that the critical start-up flow rate of the pipeline-type Spherical hydraulic turbine under no-load conditions was4.5m~3/h,the stable operational flow rate was 5m~3/h,and the stable operational flow rate under load conditions was 8m~3/h.Additionally,the reliability of numerical simulation using the SDOF solver was further demonstrated by conducting speed characteristic tests on hydraulic turbines.Numerical simulation revealed that the relationship between flow rate and hydraulic turbine speed was linear under no-load conditions.The start-up time of the turbine was 0.224 s at a flow rate of 5m~3/h,and only 0.128 s for a flow rate of 9m~3/h.(2)The starting characteristics,speed characteristics,and internal flow characteristics of six types of hydro turbines with wing chord length c/d of 0.1;0.12;0.14;0.16;0.18 and 0.2were compared and analyzed by using the SDOF solver.The results show that the hydro turbine with the wing chord length c/d of 0.2 has the highest average rotational speed,the shortest startup time and the best start-up performance.And the airfoil chord length will lead to different attached vortices of the blades,different vortex distribution characteristics and flow separation degree,and on the blades with larger airfoil chord length,the airfoil suction surface shows better attached flow and more regular flow field.(3)Based on the airfoil chord length c/d of 0.2,the starting characteristics and internal flow characteristics of hydro turbines with different number of blades under no-load conditions are studied,and the turbine speed stability of 5-blade turbine under no-load conditions is better than that of 4-blade turbine.The starting characteristics and power characteristics of the hydraulic turbine with 4 and 5 blades under load conditions are studied.The starting performance of the turbine with 5 blades is better than that of the turbine with 4 blades,and the power coefficient of 5 blades Cp=1.106 is slightly higher than that of the turbine with 4 blades Cp=1.079,which shows that the hydraulic turbine with 5 blades is optimal.(4)Using the similar conversion principle of Spherical hydraulic turbine,the relevant parameters of DN50 Spherical hydraulic turbine are converted to DN500 pipeline,and based on the research results,the economic benefits that can be generated by installing Spherical hydraulic turbine in DN500 pipeline in a local area of a city are predicted.It is predicted that a single water supply node using the device can generate an average of 4.17 k W-h per day,and its estimated cost savings of ￥1 3,380 for a single water supply node in five years,with a return on investment of 324%,which has significant economic benefits.This study fills in the theory of transient start-up characteristics of Spherical hydraulic turbine and provides some reference basis for its engineering application.