Author
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Robinson, Kerry |
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Cook, Kevin |
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Hanson, Gregory |
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Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Proceedings Publication Acceptance Date: 8/1/1998 Publication Date: N/A Citation: N/A Interpretive Summary: As water approaches and drops over an overfall the flow velocity exerts forces on the overfall boundary. Little information exists about the direction and velocity in the circulating water. This study measured the magnitude and direction of these flow velocities with an acoustic probe. The highly turbulent water below an overfall causes some erroneous readings. The results clearly show the circulation patterns at an overfall and they provide insight into the forces that cause headcut erosion. This information should be of interest to researchers and those interested in erosion prediction. Technical Abstract: The velocities and circulation patterns were measured and characterized for flows in the vicinity of an aerated straight drop overfall. The velocity vectors were determined for multiple tailwater levels at a constant flow rate and for multiple flow rates at a constant tailwater level. An acoustic Doppler velocimeter (ADV) was used to acquire three-dimensional component flow velocities along the channel centerline. The ADV probe performed well in areas of relatively low flow velocity and low air entrainment, but the probe did not perform well in areas with high flow velocity and high air entrainment. The velocity measurements are presented, and the near boundary flow velocities agreed well with previously measured boundary stresses. The velocities near the vertical wall and horizontal floor were observed to be similar in magnitude for a range of tailwater elevations and discharges. These velocity field measurements enhance our understanding of headcut erosion processes. |
