Abstract
Fluctuating bottom-pressures on stepped chutes are relevant for the spillway design. An abrupt slope reduction causes a local alteration of the bottom-pressure development. Little information is available regarding the air–water flow properties near an abrupt slope reduction on stepped chutes, particularly on the local pressure evolution. Nevertheless, the option of providing a chute slope reduction may be of interest in spillway layout. The experiments presented herein include pressure distributions on both vertical and horizontal step faces, subsequent to an abrupt slope reduction on stepped chutes. A relatively large-scale physical model including abrupt slope reductions from 50° to 18.6° and from 50° to 30° was used, operated with skimming flow. The data indicate a substantial influence of the tested slope reductions on the bottom-pressure development. In the vicinity of the slope reduction, the mean pressure head near the edge of the horizontal step face reached 0.4 to 0.6 times the velocity head upstream of the slope reduction, for critical flow depths normalized by the step height ranging between 2.6 and 4.6.
Highlights
Academic Editor: Marco FranchiniThe knowledge of the fluctuating bottom-pressure distribution is important to ensure the structural integrity of smooth and stepped chutes, especially under negative pressures.For stepped chutes with a constant bottom slope, the mean or fluctuating pressures acting on the steps were assessed by several laboratory studies (e.g., [1,2,3,4,5,6,7,8,9,10,11,12,13])
On the horizontal face of the step, a typical S-shape pressure distribution was observed, with maximum pressures occurring at the so-called impact flow region, near the outer edge of the step, whereas minimum pressures were noticed on the upstream half of the step face, due to the boundary separation of the recirculating flow (e.g., [3,4,7,8,11,12,13])
On the vertical face of the step, distinct pressure profiles were obtained in function of the pressure percentile, generally with negative pressures near the upper edge of the vertical face, for the mean and lower pressure percentiles, and positive pressures near the step corner (e.g., [3])
Summary
Academic Editor: Marco FranchiniThe knowledge of the fluctuating bottom-pressure distribution is important to ensure the structural integrity of smooth and stepped chutes, especially under negative pressures.For stepped chutes with a constant bottom slope, the mean or fluctuating pressures acting on the steps were assessed by several laboratory studies (e.g., [1,2,3,4,5,6,7,8,9,10,11,12,13]). The knowledge of the fluctuating bottom-pressure distribution is important to ensure the structural integrity of smooth and stepped chutes, especially under negative pressures. On the horizontal face of the step, a typical S-shape pressure distribution was observed, with maximum pressures occurring at the so-called impact flow region, near the outer edge of the step, whereas minimum pressures were noticed on the upstream half of the step face, due to the boundary separation of the recirculating flow (e.g., [3,4,7,8,11,12,13]). Empirical dimensionless formulae were developed to estimate the mean and extreme pressure profiles on the horizontal and vertical step faces of a steeply sloping stepped chute (e.g., [3])
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