Temperature Measurement · Glossary

What is Wake Frequency?

thermowell vortex sheddingTemperature Measurement

Wake frequency is the frequency of vortices shed by flow past a thermowell; if it approaches the well natural frequency, the well can fail.

Wake Frequency Explained

Flow past a cylinder sheds vortices alternately, pushing the thermowell sideways (and in line at half the force). Resonance with the natural frequency causes large stresses and fatigue.

ASME PTC 19.3 TW checks frequency limits, steady and dynamic stress, and pressure rating. Shorter or thicker wells, or wells with helical strakes, raise the margin.

Wake Frequency Formula

f_s = St × V ÷ B

f_s	shedding frequency (Hz)
St	Strouhal number, depends on Reynolds number
V	flow velocity (m/s)
B	well tip diameter (m)

Calculators for Wake Frequency

CalculatorVortex Flow Meter CalculatorFree online calculator with formula and worked example.CalculatorPipe Flow Velocity CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is Wake Frequency?

Wake frequency is the frequency of vortices shed by flow past a thermowell; if it approaches the well natural frequency, the well can fail.

Which standard covers wake frequency?

ASME PTC 19.3 TW, the 2010 and later editions, replaced the older simple frequency ratio method.

Does the sensor inside matter?

Its mass is included in the natural frequency calculation, but the well dominates.

Learn more on the blog

Thermocouple and RTD installation precautions

A practical guide on instrumentationblog.in with more detail on wake frequency and how it is applied on real plants.

Read Full Article

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