Discussion
A vortex flowmeter works on the principle that the Strouhal number of 0.2 is a constant over a wide range of flow rates. If the bluff-body diameter in the flowmeter is 20 mm and the piezo-electric transducer registers the vortex shedding frequency to be 10 Hz, then the velocity of the flow would be measured as
Answer: B
The flow velocity is 1 m/s.
The Strouhal number relates shedding frequency \(f\), body diameter \(d\) and velocity \(V\):
\[ \begin{aligned} St &= \frac{fd}{V} \\ V &= \frac{fd}{St} = \frac{10 \times 0.020}{0.2} \\ &= 1\ \text{m/s} \end{aligned} \]
The other options differ from it by factors of ten, the usual result of a unit slip with the diameter or the frequency. Keeping \(d\) in metres and \(f\) in hertz gives 1 m/s.
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