Study On Drainage Performance Of Single-Outlet Siphon Drainage System

With the rapid development of urban construction,the number of buildings with large space,capacity and span is increasing,due to the smaller displacement,more drainage pipes,horizontal collection pipework need to set the slope and etc,the traditional gravity drainage cannot fully meet the modern Demand for large construction roof drainage.Many projects have begun to use more excellent siphon rainwater drainage system,but the existing siphonic roof drainage system design and calibration method is based on the full pipe flow,the understanding for the siphon start and the formation process is not enough depth.The length of the horizontal collection pipework in the existing system is designed base on the roof structure,without taking the impact of the siphon drainage performance into account.And there is no relevant restrictions for the horizontal collection pipework length in the existing specifications.Study mainly focus on the dynamic variation law of system parameters and the method of calibrating the length of horizontal collection pipework.Firstly,the siphon drainage system is analyzed theoretically,the forming conditions and judgment criteria of the siphon drainage system are summarized,and the performance index of the siphon drainage is put forward.Then build a single-outlet siphon drainage system test bed,use the indirect method to measure the dynamic variation law of system parameters under different flow rate.Flow pattern and pipe parameters are divided into three types according to the water replenishment(large flow conditions:Q>80%,medium flow conditions:55%<Q<80%,small flow conditions:30%<Q<55%),and use literature test data to verify.Secondly,the numerical calculation model of siphonic roof drainage system is established by STAR-CCM + software and VOF method.The process of siphon formation under large flow conditions is simulated.The accuracy and feasibility of the numerical calculation method are proved by comparing the change of the system flow curve,the trend of the system parameter curve,the siphon start time,the maximum displacement and the experimental results.In addition,select several pipe structure parameters to do sensitivity analysis of the influencing the siphon start-time.Result is that the horizontal pipework length,vertical pipework diameter,horizontal pipework diameter and tail pipe length have great influence on siphon start-time.And propose to use upstream pipe volume to simplify the siphon start-time calculation.Finally,focus on the problem of the long horizontal pipework of the existing siphon drainage system,the thesis put forward a method of calibrating the length of horizontal pipework.The method is based on the Bernoulli equation,the continuity equation and other theoretical formula,and combine the numerical calculation results to obtain the simplified calculation formula of Horizontal pipework-Maximum displacement(Q-L2)、Horizontal pipework-Siphon start-time(T1-L2).Set the two conclusions as the restrictions of horizontal pipe length.And then according to the local weather parameters,roof structure,gutter size and other parameters to further get the maximum horizontal pipework length L2,providing reference for engineering design.