Fluid Mechanics and Acoustics Laboratory - UMR 5509

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Home > Research Support > Scientific instrumentation > Techniques > LDV - Laser Doppler Velocimetry

LDV - Laser Doppler Velocimetry

LDV - Laser Doppler Velocimetry

The Laser Doppler Velocimetry, also called LDV, or the laser doppler anemometry when it is specifically about wind velocity measurements, was developed in the sixties with the first lasers. Yep & Cummins (1964) were the first to measure velocities in water, the first LDV application in the air was led by Rolfe & Huffaker (1967). The application range of this technique is wide: liquids, gas and multi-phasis environments. It is possible to use it from really slow velocities to supersonic velocities. Nonetheless, the execution of the LDV requires some technical mastery of the system. Its principle upside is that this velocity measurements technique is a non-intrusive one.

A LDV system is an instrument measuring the Doppler shift of the light diffused by a moving particle that follows perfectly the flow.

Physical principles

  • The LDV principle is based on the measurement of the velocity of thin particles injected (seeded) in a fluid flow.
  • The particles are considered small enough to follow perfectly the flow. The particles velocity then matches the fluid one.
  • The particles are lit in a very small volume by a laser beam and diffuse this light in all the directions. It is a point measurement.
  • The diffused light is measured on a point (out of the flow) by a photosensor.
  • The particle velocity is determined from the Doppler effect.

Concept schematic

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LDV measurements system (Dantec Dynamics)