Laser Doppler velocimetry

Summary

Laser Doppler velocimetry, also known as laser Doppler anemometry, is the technique of using the Doppler shift in a laser beam to measure the velocity in transparent or semi-transparent fluid flows or the linear or vibratory motion of opaque, reflecting surfaces. The measurement with laser Doppler anemometry is absolute and linear with velocity and requires no pre-calibration. Technology origin The development of the helium–neon laser (He-Ne) in 1962 at the Bell Telephone Laboratories provided the optics community with a continuous wave electromagnetic radiation source that was highly concentrated at a wavelength of 632.8 nanometers (nm) in the red portion of the visible spectrum. It was discovered that fluid flow measurements could be made using the Doppler effect on a He-Ne beam scattered by small polystyrene spheres in the fluid. At the Research Laboratories of Brown Engineering Company (later Teledyne Brown Engineering), this phenomenon was used to develop the first las

Official source

https://en.wikipedia.org/wiki/Laser_Doppler_velocimetry

About this result

This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.

Related publications (23)

Related publications

Related people (8)

Related people

Related units (2)

Related units

Related concepts (3)

Particle image velocimetry (PIV) is an optical method of flow visualization used in education and research. It is used to obtain instantaneous velocity measurements and related properties in fluids.

The Doppler effect or Doppler shift (or simply Doppler, when in context) is the apparent change in frequency of a wave in relation to an observer moving relative to the wave source. It is named afte

Velocimetry is the measurement of the velocity of fluids. This is a task often taken for granted, and involves far more complex processes than one might expect. It is often used to solve fluid dynam

Related concepts

Related courses (2)

Related courses

Related lectures (5)

Related lectures

Use of compact Laser Doppler Velocimetry in reduced scale model testing of hydraulic machines

Loïc Andolfatto, François Avellan, Vincent Berruex, Andres Müller, Masashi Sakamoto

Laser based flow survey methods such as Laser Doppler Velocimetry (LDV) or Particle Image Velocimetry (PIV) have long been used for studying the flow in hydraulic machines. Even if the results have crucially improved our understanding of potentially destabilizing flow patterns in the draft tube at off-design conditions and the prediction of the stable operating range, these techniques are not systematically used for reduced scale model measurements in the frame of customer acceptance tests or development projects. In a not too distant past, the price, size and complexity of the necessary equipment and procedures exceeded the acceptable range for these projects. Recent developments however made them more accessible. Furthermore, the collaboration with experienced research institutes provides the necessary know-how as well as an added academic value by providing researchers with realistic test cases. This work reports a case study for which a compact LDV probe was used to measure the velocity field in the draft tube cone of a reduced scale physical model of a Francis turbine. The axial and tangential velocity profiles were established by performing measurements at several radial positions between the turbine centreline and the cone wall. The overall objective was the validation of numerical flow simulations across the entire operating range of the turbine, from partial to full load.

2018

Interaction of a pulsating vortex rope with the local velocity field in a Francis turbine draft tube

François Avellan, Alberto Bullani, Matthieu Dreyer, Arthur Tristan Favrel, Christian Landry, Andres Müller, Steven Roth

Acoustic resonances in Francis turbines often define undesirable limitations to their operating ranges at high load. The knowledge of the mechanisms governing the onset and the sustenance of these instabilities in the swirling flow leaving the runner is essential for the development of a reliable hydroacoustic model for the prediction of system stability. The present work seeks to study experimentally the unstable draft tube flow by conducting a series of measurements on a reduced Francis Turbine model. The key physical parameters and their interaction with the hydraulic and mechanical system are studied and quantified. In particular, the evolution of the axial and tangential velocity components in the draft tube cone is analysed by means of Laser Doppler Anemometry. Combined with the calculation of the instantaneous vortex rope volume based on flow visualization and the measurement of the pressure fluctuations, the nature of the auto-oscillation in the draft tube flow is investigated.

IOP science2013

Assessment of the optic nerve and retinal oxygenation using the techniques of phosphorescence quenching by oxygen and laser doppler flowmetry

Stéphane Chamot

EPFL2002