Tainter gates become dynamically stable at large gate openings, even though they usually exhibit intense dynamic instability at small gate openings. To assess which factors govern this stability at large openings, model investigations were conducted. The present study focuses on discharge characteristics and hydrodynamic pressures at large gate openings. The model tests were conducted using a 1/27-scaled 2-dimensional model of the Folsom Dam Tainter gate. The instantaneous flow-rate coefficient was obtained from LDV measurements of flow velocity accompanying periodic changes in the gate opening. Measurements of the hydrodynamic pressure associated with the flow-rate variation were also used to determine instantaneous flow-rate coefficients. Comparison of the directly measured instantaneous flow-rate coefficient form LDV measurements with that obtained from pressure measurements suggests that the flow field is less receptive to disturbances due to gate motion at larger gate openings. With increased gate openings, the fluctuating fluid force acting on the gate decreases, making the gate dynamically stable.

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