Abstract
Flow over bottom racks is highly turbulent, three-dimensional and spatially varied. The design of bottom intake systems has mainly been studied in the laboratory. The comparison of existing experimental studies shows large deviations in the definition of design parameters such as wetted rack length. Each experimental study is limited to a single bar type or to a low range of void ratios, which makes it difficult to generalize the observed data. A combination of empirical, dimensional and inspectional analysis is presented as a useful tool to reduce the number of variables with influence in the design parameters, such as the wetted rack length or the mean discharge coefficient. This work includes a broad experimental campaign in which wetted rack length and mean discharge coefficient are characterized using five different bottom racks with different void ratios (area between bars divided by total area). T-shaped flat and circular bars are considered as well as five different longitudinal slopes. Empirical and inspectional analyses have allowed us to verify, in two different ways, the relation between wetted rack length and incoming flow through potential functions. The influence of the viscous forces has been studied as a function of the incoming flow. Similar results may be obtained when analysing the Froude number at the beginning of the rack, depending on the wetted rack length. A new formulation for calculating the mean discharge coefficient and wetted rack length is proposed.
Highlights
The design of bottom intakes to derive flow at stepped rivers has been broadly studied by hydraulic engineers
Are discharge coefficient, characterized usingoffive different bottom racks with different void ratios, m
Comparing values of wetted rack lengths proposed by different authors, this length may differ by up to double in some cases [4,5,6]
Summary
The design of bottom intakes to derive flow at stepped rivers has been broadly studied by hydraulic engineers. Dimensional, empirical and inspectional analyses are taken to define variables such as wetted rack length and discharge coefficient, which influence the design parameters of bottom rack systems. Comparing values of wetted rack lengths proposed by different authors, this length may differ by up to double in some cases [4,5,6] This is principally due to the variation of the experimental conditions used to adjust the discharge coefficient, such as the shape and width of the bars, the spacing between them, the void ratio, the approximation flow conditions, the initial flow depth h0 , or the longitudinal rack slope, tanθ, [4,5,6,7]
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