Study On The Hydraulic Characteristics Of The Gradual Change Section Of The Open Channel

The crossing is an important node building in the open channel water transmission project,and the overflow capacity of the crossing itself directly affects the overflow capacity of the whole open channel water transmission project.Therefore,it is of high practical and economic significance to study the influencing factors of the overflow capacity of the gradual change section of the open channel to improve the water transmission efficiency of the water transmission project.In this paper,based on the structural parameters of a typical ferry and the measured water condition data,Flow-3D fluid dynamics calculation software is used to establish the ferry model and study the influence of the structural form of the tapering section on its overflow;the influence of the structural form of the tapering section on its local head loss coefficient;and considering the twisted surface on both sides of the tapering section,the symmetry of its structure is taken into account,and the left and right sides of the tapering section are set as twisted surface when the tail pier is added to the outlet tapering section to select the optimal solution to eliminate the water surface fluctuation to increase the water transmission capacity.The results show that(1)under the condition of free outflow of the open channel gradient section,the overflow flow has a good function relationship with the net width of the overflow at the end of the gradient section and the total upstream head.(2)The smaller the bottom slope of the inlet and outlet gradient section,i.e.,the lower the trough body,the greater the overflow capacity of the trough.When the upstream and downstream water levels are certain,the overall overflow of the ferry has a good quadratic function relationship with the difference in elevation between the bottom of the upstream and downstream of the inlet and outlet gradient section ?Z.(3)In the upstream trapezoidal channel section of the ferry,the Froude number decreases with the increase of the upstream and downstream bottom slopes;the Froude number increases with the increase of the upstream and downstream bottom slopes in the channel body section;the Froude number decreases with the increase of the upstream and downstream bottom slopes in the downstream trapezoidal channel section of the ferry.(4)The local head loss coefficient of the inlet gradient section of the ferry has a good exponential function relationship with the contraction angle of the water surface in the gradient section.(5)By analyzing the simulation results of each tail pier model,the sill-shaped tail pier can not eliminate the Carmen vortex street,and the conical tail pier can eliminate the Carmen vortex street.The water level along the tapered tail pier is smoother and there is no fluctuation of water level in the trough body;the Froude number is also more stable in the trough body;the turbulent kinetic energy dissipation rate near the exit asymptotic section is significantly smaller than that of the prototype ferry;the total head of 15 m long tapered total head decreases the least in the exit asymptotic section;the effect of 15 m long tapered twisted surface tail pier is better.