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flow pattern, dye injection and a digital camera (model; Olympus c-5050z)
with a strong light were used.
4. Results and Discussions
Flow regimes of nappe and skimming flow are shown in Figs. 4 and 5,
respectively. Nappe flow occurs at low flow rates and for relatively large
step height. Dominant flow features include an enclosed air pocket, a free-
falling nappe impact and subsequent hydraulic jump on the downstream
step. Air inception occurs from the step edge, but most air is entrained
through a free-falling nappe impact and hydraulic jump. Air pocket also
has an important role to the air entrainment. The flow accelerated in the
downstream direction until a deflected nappe took place. At take-off, free
surface aeration was observed at both upper and lower nappes with addi-
tional air entrainment at the impact followed by jet breakup.
Fig. 4. Nappe flow.
Fig. 5. Skimming flow.
