Hydraulic Performance And Optimizations Of The Curled Up Type Of Siphon Outlet Conduit Pump Device

Outlet conduit of pumping station is an important part of the pumping station engineering hydraulic structures.For low-lift vertical axial flow pump system,siphon outlet conduit has the features of simple cut-out way and low head loss.Therefore,in engineering design of vertical axial flow pump devices,siphon outlet conduit is often used.In this paper,the original pump model is based on a large pumping station pump model as the prototype.It adopts curled up type of siphon outlet conduit,which can better adapt to the local terrain conditions and shorten the longitudinal length of pump stations,thus saving the construction investment and having a good stability of pump station.At present,the domestic and overseas research on curled up type of siphon outlet conduit is not much.Therefore,the hydraulic characteristics of this type of outlet conduit remain to be further understand.In this paper,CFX software is conducted to perform numerical simulations of the original pump model.The calculation results show that the inflow pattern of the original pump model has a relatively high uniformity in flow rate and a smooth streamline,but the streamline of outlet conduit,which has many vortexes,is overall chaotic.The head loss of outlet conduit mainly comes from the bending section.When water flows through the outlet conduit,due to the recovery of eddy kinetic energy,the vorticity decreases gradually.Whereas when water flows through the exit section,the vorticity increases,mainly because there are vortexes near the export of outlet conduit.The external characteristic of the original pump model is predicted,and the comparison between the predicting outcome with the test data shows that the two trends are basically consistent.In working conditions of small flow rate,the predicting outcome had a slightly smaller data head and higher efficiency compared with the test date,and the differences are very small.Besides,in the design conditions and heavy traffic working conditions,they are highly consistent,which shows that the calculation results are trusted.Aiming at optimizing the existing problem of the outlet conduit,through the analysis of distribution relationships of the distance between section center and cross section area,it is found that the exit section of the original pump model's outlet conduit is significantly large.To solve this problem,we can raise the elevation of bottom part of the outlet conduit exit,thus reducing the area of exit section,optimizing the flow pattern,improving the efficiency of the pump station and reducing engineering volume at the same time.After optimizing the decline period of the outlet conduit of the original pump model,the optimized decline period(scheme 1)got obvious improvements:the average vorticity of each typical sections got decreased;the head loss of outlet conduit got reduced;the axial velocity distribution uniformity on the outlet section increased by more than 13%;and in various conditions,the pump efficiency increased by 0.19%to 2.05%than that of the original pump model,and high efficient area widened obviously.To further optimize overall outlet,the area of the cross section of hump section of the original pump model was changed,which can ensure that the distributions of the distances between the outlet cross section center and cross section areas are approximately linear.The optimized outlet(scheme 2)can greatly eliminate the vortexes of the original pump model's outlet conduit:the average vorticity of each typical sections got further decreased;in various conditions,the head loss of outlet conduit reduced by more than 0.03m;the axial velocity distribution uniformity on the outlet section increased by approximately 18%,reaching about 88%;in various conditions,pump efficiency increased by 0.23%to 3.64%than that of the original pump model,and in the heavy traffic condition,the improvement of efficiency is most obvious.The influence of incoming flow disturbance to the performance of the pump was studied.Due to the asymmetric operation,water cannot flow smoothly into inlet conduit.By comparing the hydraulic characteristics,it is found that in condition of incoming flow disturbance,the flow pattern of inlet conduit's inlet section got worse,and the axial velocity uniformity of inlet conduit's outlet section decreased to some degree.Consequently,under various conditions,the efficiency of the original pump decreased by 0.26%to 1.24%.Bedsides,the flow pattern of outlet conduit was also influenced.Compared to the original pump model,it is more turbulent:the range of vortexes expanded;the vorticity of each typical sections and the head loss of outlet conduit got decreased;the axial velocity uniformity of inlet conduit's outlet section got decreased.In actual operation of pump station,the income flow disturbance,such as the asymmetric operation and side inlet,should be avoided.