Free nappe over a sharp-crested weir: pressure condition beneath the nappe For a ventilated, freely falling nappe (free nappe case), determine the pressure condition. Choose the correct statement.
Mechanical Engineering
Hydraulics and Fluid Mechanics
Difficulty: Easy
Choose an option
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AThe pressure below the nappe is atmospheric
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BThe pressure below the nappe is negative
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CThe pressure above the nappe is atmospheric
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DThe pressure above the nappe is negative
Answer
Correct Answer: The pressure below the nappe is atmospheric
Explanation
Concept/Approach
- A free nappe is ventilated on its underside, allowing atmospheric air to enter. Hence the pressure beneath the nappe equals atmospheric pressure. If not ventilated, sub-atmospheric (negative gauge) pressure may develop and the nappe can cling to the crest, which is not the free-nappe case.
Final AnswerThe pressure below the nappe is atmospheric