Analysis Of Characteristics Of Multi-outlet Siphonic Drainage System

The siphonic roof drainage system is characterized by the features such as its strong drainage capacity,no need for slopes in suspension pipes,a small number of vertical pipes and self-cleaning ability,which is particularly suitable for public buildings or industrial buildings with large roofs that have been built in recent years.However,the multi-outlet siphonic roof drainage system is designed on the basis of designed rainfall event and the rated discharge flow rate of the outlet,actually discharge flow rate of each outlet in a same system is not the same.And the pipeline of drainage system is designed according to the form of a roof gutter without considering the effect of pipeline layout on the discharge flow.In order to solve these problems,this paper mainly studied the flow characteristics of double-outlet siphonic drainage system and the effect of pipeline parameters on the drainage capacity of the system through experiments and numerical simulations.Based on the rules of double-outlet flow,the theoretical calculation formula of maximum discharge of multi-outlet system was derived.Firstly,the siphonic drainage system is introduced from several aspects such as system configuration and working principle,and four factors that affect the drainage performance of the siphon system are analyzed.Then,by setting up a double-outlet siphonic drainage system experimental bench,analyzed the perspective of experimental phenomena and experimental results under different inflow rates of three experimental models,including the outlets in the double-outlet siphonic drainage system,the single-outlet siphonic drainage system with the double-outlet siphonic drainage system,and blocking an outlet.Getting the following conclusions,under the design criteria rainfall event in the double-outlet system,the discharge rate of the outlet which is corresponding to the single-outlet system is smaller than the discharge rate of the single-outlet,and there is a larger discharge rate of the outlet which near the vertical drainage pipe in the double-outlet system;and the blocking of the outlet can cause abrupt changes in the negative pressure,which may cause serious malfunction.Secondly,the influence of the length of the suspension pipe of the double-outlet siphonic drainage system on the system performance was analyzed by numerical simulation.Using the same numerical calculation model as the experimental model and comparing the flow patterns and parameters of the two models,the correctness of the numerical calculation method is proved.Two numerical calculation models were established,including changing the distance from the outlet which is near vertical drainage pipe to the vertical drainage pipe and changing the spacing of the rainwater outlets.Comparing the calculation results of the discharge capacities of the two model systems,it is found that the larger the distance from the outlet near the vertical drainage pipe to the vertical drainage pipe is,the smaller the discharge flow is,and the larger the spacing between the outlets is,the smaller the discharge flow is.The sensitivity analysis to the discharge of the two models is also made,found that compared to the distance between the outlets,the distance between the near vertical drainage pipe outlet and the vertical drainage pipe has a greater impact on the system discharge flow.The rainwater outlet should be placed as close to the rainwater riser as possible to increase the system discharge flow.Finally,the calculation formula of double-outlet is deduced by using the Fluid Mechanics energy equation and the flow law in the pipeline,and verified by the double-outlet experimental under large flow rate conditions,which has a good consistency.Then the double-outlet drainage system is subsequently analyzed the influence of the drag coefficient on the system discharge flow by this formula.The double-outlet discharge flow calculation formula is extended to multi-outlet,and the multi-outlet system discharge flow calculation formula is used to obtain theoretical calculations,as the number of rainwater outlets increases,the average unit discharge flow rate of outlets shows a downward trend,and when the number of rainwater outlets by one side exceeds 6,the rate of leakage of traffic was less than 10%.In order to simplify the calculation of multi-outlet system discharge flow,a simplified calculation formula for the number of rainwater outlets is fitted.Applying this method to an actual project,it is found that the system drainage capacity is much smaller than the design rainwater flow rate,and optimization methods for system design are proposed,providing a reference for engineering design.