Numerical Simulation And Experimental Study On The Increase Of Flow Capacity In Typical Aqueduct Section

As an important water conveyance structure for crossing obstacles,aqueducts are widely used in large-scale water transfer projects.In the middle route of the South-to-North Water Transfer Project,27 aqueducts play an important role in crossing canals,roads,and other obstacles.As a major water conservancy project for the allocation of water resources in China,the South-to-North Water Transfer Project is of strategic significance in optimizing the temporal and spatial allocation of water resources in China.With the successful completion of the design of the middle route project to increase the flow of water,during the period of large flow water transfer,the aqueduct section appeared to have the phenomenon of waves alternately surging and even slapping the top beam of the aqueduct.This complex wave flow pattern will not only interfere with the normal operation of water conveyance but also affect the safety of the aqueduct structure to a certain extent.Therefore,the mechanism of the complex wave flow pattern of the aqueduct is studied,and then a wave reduction scheme is put forward.It is of great value in enhancing the overcurrent capacity and stability of the aqueduct.As a throat structure to limit the improvement of overcurrent capacity of the south-to-north water transfer project,the aqueduct adopts the method of numerical simulation and hydraulic experiment to study the scheme of complex fluctuation reduction and overcurrent capacity improvement under the condition of large flow water transfer.The main research contents include:(1)A three-dimensional numerical simulation model of a typical aqueduct section is established in Flow-3D fluid calculation software through field investigation and data collection.The hydraulic model test is used to verify and analyze the numerical simulation results.Based on the measured data to calibrate the model parameters,the results show that the relative error between the numerical simulation results and the field measured velocity and water depth data is less than 5%,and the data are in good agreement with the data.The phenomenon of wave alternating surge in the trough body is successfully repeated,which is consistent with the field observation,ensuring the accuracy of the numerical model in simulating the complex wave flow pattern of the aqueduct building.(2)The numerical simulation and hydraulic model experiment are used to study the cause of wave alternating surge in the trough body under the condition of large flow.The results show that both numerical simulation and hydraulic model experiments successfully reproduce the phenomenon of "Karman vortex street" and wave surge at the outlet of a typical double-hole aqueduct.Through the comparative observation of the velocity field and streamline at the outlet of the aqueduct,it is found that the Karman vortex street has a local water blocking effect on the upstream flow.It is determined that the Karman vortex street at the outlet of the aqueduct is the source of alternating surge waves according to the comparison between the shedding lift coefficient of the vortex street and the alternating wave resurgence frequency.(3)According to the mechanism of complex flow pattern in the groove body,the scheme of "spindle type" diversion pier is put forward,and experiments are carried out on four different diversion pier lengths under three flow levels.The results show that the "spindle type" diversion pier can improve the inlet and outlet flow pattern of the aqueduct,greatly reduce the water blocking effect of the vortex street on the upstream flow,and the maximum amplitude reduction of the aqueduct body is more than 80%.After the comparative test of the combination of diversion piers of different length,the best performance-to-price ratio combination is put forward that the aspect ratio of inlet and outlet diversion piers is AR=L/W 1.5,2.0 respectively.(4)From the point of view of wave suppression and overcurrent capacity improvement,a "closed" scheme is proposed to simulate 8 different upstream and downstream water level differences,and the feasibility of the "closed" scheme is verified on four aqueducts of different forms.The results show that the "closed" scheme has a good inhibition effect on wave alternating backwelling phenomenon.When the upstream water level reaches the top of the channel,the "closed" scheme can increase the flow capacity of the aqueduct by 31.0%.After the application of the "closed" scheme,the overcurrent capacity of the four different forms of aqueducts has been improved in varying degrees,which confirms the feasibility of the "closed" scheme.