How does laser Doppler velocimetry measure fluid flow?

Laser Doppler velocimetry is an optical technique used to measure the velocity of transparent or semi-transparent fluid flows, as well as the motion of opaque reflecting surfaces. It relies on the Doppler shift in a laser beam to provide an absolute and linear measurement that needs no pre-calibration. However, at least one expert source notes that using the term Doppler for standard laser Doppler velocimeters is technically a misnomer since no Doppler shift measurement is actually involved.

What we know

• Laser Doppler velocimetry is an optical method used to measure fluid flow. [1]
• The technique uses the Doppler shift in a laser beam to measure velocity in transparent or semi-transparent fluid flows. [2]
• Measurements taken with laser Doppler anemometry are absolute and linear with velocity, requiring no pre-calibration. [2]
• Laser surface velocimeters use the laser Doppler principle to evaluate back-scattered laser light from a moving object. [3]

Still open

• It is debated whether the term Doppler is appropriate, with J. Cimbala stating that no Doppler shift measurement is actually involved in a laser Doppler velocimeter.

Where to go next

• how it workedHow do laser surface velocimeters work?
• the bigger pictureWhat is bulk fluid movement quantification?
• a case in pointHow do positive-displacement flowmeters operate?
• what followedWhat are the common industrial applications of flowmeters?
• compared withHow do ultrasonic flow meters compare to optical methods?
• an unexpected connectionWhy might calling it a Doppler device be technically incorrect?Although the technique is universally named after the Doppler shift, experts have argued that no actual Doppler shift measurement takes place in the device.

Sources

• [1]laser Doppler velocimetry (Wikidata Q1420475) · CC0 1.0
• [2]Laser Doppler velocimetry · CC BY-SA 4.0
• [3]Laser surface velocimeter · CC BY-SA 4.0
• [4]List of laser articles · CC BY-SA 4.0
• [5]Flow measurement · CC BY-SA 4.0