Vortex Flow Meter Calculator
Check a vortex meter application: velocity in the bore, Reynolds number and the vortex frequency from the meter K factor or from the Strouhal relation.
- v = Q ÷ A = 4.244 m/s
- Re = ρvD ÷ µ = 211,400
- f = St × v ÷ w = 0.2 × 4.244 ÷ 14 mm = 60.63 Hz
Vortex Shedding Equations
f = Q × K (meter K factor)
Re = ρ × v × D ÷ µ
St is the Strouhal number (close to 0.2 and nearly constant over a wide Reynolds range, which makes the meter linear), v the velocity, w the bluff body width, Q the volume flow and K the calibrated pulses per unit volume from the meter datasheet.
Worked example
30 m³/h of water in a 50 mm bore gives v = 4.24 m/s and Re ≈ 211,000. With a 14 mm bluff body and St = 0.2 the vortices shed at about 61 Hz.
Frequently Asked Questions
How does a vortex flow meter work?
A bluff body sheds vortices alternately from each side. Their frequency is proportional to velocity, so counting them gives flow.
What is the Strouhal number?
A dimensionless number relating shedding frequency, velocity and bluff body width. It stays close to 0.2 over a wide range of Reynolds numbers.
Why does a vortex meter cut off at low flow?
Below a minimum Reynolds number or dynamic pressure the vortices become weak and irregular, so the meter forces its output to zero.
Learn more on the blog
Types of flow meters
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
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