Effects of Tunnel Dam Gate Lip Geometries on Downpull Force Coefficients

Vertical lift tunnel type gates are subjected to hydrostatic and hydrodynamics forces created due to the operation conditions over a large variety of gate openings, flowrates and heads. The impact of the flow over and beneath the gate caused generation of two forces, downward force on the gate within the gate shaft and upward force on the gate bottom surface. The difference between these two forces is termed as downpull force by which the safe performance of gate can be evaluated. The downpull force is influenced mainly by the pressure heads on the top and bottom of the gate surface beside the jet velocity issued below the gate. The gate geometry has also been found as major factor may affect its response against pressures exerted by flow, especially near and around the gate lip. In this research, a random hydraulic model was conducted to examine the effect of many gate lip shapes on the downpull force coefficients. More than 48 experimental runs are made. The result specifies that the behavior and magnitudes of top pressure coefficient is varied uniformly from high to low values as the gate openings increase, and seem to be not much more sensitive to changes in gate lip geometry. Some fluctuation is observed in the values and distribution of the bottom pressure coefficient due the changes in gate geometries and openings, so that the downpull coefficient is accordingly influenced effectively by this coefficient.