Approach‐Flow Effects on Downpull of Gates

The effects of various approach‐flow conditions upon the down‐pull, the local pressures, and the discharge characteristics have been investigated for intake gates. Laser‐Doppler‐Anemometry measurements near the separation point of the gate bottom permit detailed specification of turbulence conditions. The partly strong variation of down‐pull and discharge coefficient for the different approach flows considered is traced to the sensitivity of the separated‐flow pattern near bluff bodies to freestream turbulence, and to changes in the mean‐flow incidence. For the particular gate studied, local flow separation from a protruding bottom girder and the placement of a trash‐rack‐like grid at a short distance upstream from the gate are shown to yield opposite effects on the downpull coefficient as compared to mere freestream turbulence. In analogy to the observations of flows around prisms, two separated‐flow regimes with and without reattachment are identified in the flow around the gate bottom, and the observed effects of turbulence on the downpull and discharge are interpreted in terms of changes in the separation patterns. The results can be generalized and applied to geometrical configurations other than those studied.