Research On Three-dimensional Flow Field Characteristics Of Bifurcation Area In Canal System

Bifurcation area is strategic passage in canal system,which is important to flow and sediment diversion.The flow structure of this area is complex because of the boundary.On basis of previous research,this paper is based on a scheduling pumping water project in South Asia,using model test combined with numerical simulation,the flow elements and flow field characteristics of bifurcation area in different working conditions was studied.The main achievements of this thesis are listed as following:1.The significance of studying the bifurcated flow has been indicated.The complexity of bifurcated flow has been pointed out.Reviews of the related research on this stream and the flow movement law of bifurcation area have been given as well as the progress of the numerical modeling and its application in the current calculation of this flow.2.In different working conditions,the three-dimensional flow field characteristics of upstream and downstream of main canal,dilution zone and branch canal in bifurcation area have been researched,the laws as following: the velocity of water flow of upstream and downstream main canal in transverse declined from right bank to the entrance.The right bank was the mainstream zone.Taking water from canal had little influence on upstream and downstream of main canal.There were a obvious phenomenon of intense turbulence and mixture in dilution zone.The velocity gradient reached to the maximum at the interface.Water near the entrance presented conspicuous 3D characteristic.After water entering branch canal,the phenomenon of plane circulation was outstanding in left bank.Section shrinkage take place in branch canal,while hydrodynamic axis focused on the right bank,forming obvious spiral flow.By the turbulent mixture in front of the branch canal,flow pattern gradually transits to one-dimensional conventional motion along the canal.3.Based on the observation of water movement of indoor model test,the calculation model was established to analyze the hydraulic characteristics of bifurcation area where the division angle was 73°,using RNGk-? turbulence model and by means of FLOW-3D.By contrasting calculation results and model test,the accuracy and reliability of the calculation model was verified.Through the mathematical model,several hydraulic factors of bifurcation area in canal system and cross section of entrance in different conditions was analyzed.The variation of three dimensional flow velocity along depth was the key inquiry: the plane circulation in front of branch canal reduced with the increase of depth.There was a conspicuous 3D characteristic in entrance section,while the velocity distribution was different to conventional motion along the canal.4.Introducing ratio of unit width discharge,the change law of length and width of recirculation zone of bifurcation area in canal system and the variation of contraction coefficient of branch canal inlet section in different ratio of unit width discharge was emphatically introduced and the fitting formula was pushed out.The results show that the range of recirculation zone of bifurcation area increases and the contraction coefficient of branch canal inlet section decreases with the increase of ratio of unit width discharge.