Numerical Simulation Of Sluice Gate Regulated Unsteady Flow In Irrigation Canals

Contradiction between water resource's supply and demand in China is more and moresevere, but the agricultural water waste is very serious, one of the reasons which can't beignored is the flow regulation techniques in Chinese irrigation districts is backward. Sluicegate are widely used for flow control in irrigation canals, and its opening variation directlyaffects the flow state of the canal. Therefore, analyzing the transition of flow state and itsinfluence factors due to the gate opening change is of great significance to optimize gateregulation mode, and improve flow regulation techniques of the irrigation districts. Unsteady flow transition process in irrigation canals due to sluice gate regulation wasprimarily analyzed in the thesis, which included the following contents: ⑴Canal operation, gate regulation mode and flow through the sluice gate. Theadvantages and disadvantages of three commonly used operation modes in irrigation canals,namely constant upstream water depth, constant downstream water depth and constant watervolume were compared. The adoption condition of gate regulating modes, namely sequentregulation, simultaneous regulation and selection regulation was also discussed. Theequations of discharge through the gate and discharge coefficient under free or submergedflow conditions were analyzed. The discharge coefficient function of the sluice gate, whichwas fitted by Prabhata, was adopted in the programming for the numerical solution of theSaint-Venant equations. ⑵Numerical simulation of unsteady flow in irrigation canals and its result analyses.Rectangular grid Characteristic method was used in the numerical simulation, and theresearch object is a single canal, the main results are: ①When upstream water depth keeps constant and downstream discharge changes,upstream discharge and downstream water depth reached to a stable state after a certain time,and vice versa. The stable discharge at one end of the canal is the regulation object at theother end of the canal. Under the condition of the same discharge and regulating time, thelarger the discharge variation, the longer the time interval needed for the flow to reach stablestate. ②Under the condition of all other state being the same, canals operating in constantdownstream depth is better than in constant upstream depth. ③During the discharge regulating time interval, gate discharge coefficient basicallyvaries in linear mode with time, after the regulating time interval, the coefficient still varies,and the larger the discharge variation, the more severe of the coefficient variation. With thewater depth of the gate tends to stable state, the variation of the coefficient gradually becomeweak and finally it also tends to a stable state.④Within the regulating time interval, and under the condition of discharge through gatehaving no transition from free flow to submerged flow(or submerged flow to free flow), thelinear variation of discharge with time almost corresponds to variation of gate opening withtime; and under the condition of free flow transiting to submerged flow(of submerged flow tofree flow), gate opening variation with time appears in a zigzag line, which can be fitted asdifferent linear functions in different time period. After the discharge regulation, gate openingappears in a waveform, finally it reaches to a stable opening Go稳定 , which is not same to thegate opening Go调节 when discharge regulating finished, Go稳定 is lower than Go调节 whendischarge regulation is positive, while Go稳定 is larger than Go调节 when dischargeregulation is negative. ⑤Linear regulating function for gate opening was derived from the following threeconditions: The gate opening before regulating, stable gate opening after discharge throughthe gate regulated in a certain linear mode, and gradient k and intercept l of the fitted gateopening regulating curve, the discharge through gate varies basically in linear mode whengate regulated...