chapter  64
Laser Anemometry
Pages 18

Laser anemometry, or laser velocimetry, refers to any technique that uses lasers to measure velocity. œe most common approach uses the Doppler shi£ principle to measure the velocity of a žowing žuid at a point and is referred to as Laser Doppler Velocimetry (LDV) or Laser Doppler Anemometry (LDA). œis technique (also known as dual beam, di¥erential Doppler, or fringe mode technique), incorporating intersecting (focused) laser beams, is also used tomeasure the motion of surfaces, for example, in industrial applications [1]. In some special žow situations, another approach using two nonintersecting, focused laser beams known as Laser two focus (also known as Laser transit velocimetry or L2F) technique is used tomeasure žow velocity at apoint [2]. Laser illumination by light sheets is used tomake global žow measurements in a plane and is referred to as Particle Image Velocimetry (PIV) [3]. œe strength of PIV (including particle tracking velocimetry) lies in its ability tocapture instantaneous velocity Ÿelds, extract turbulence structures within the žow, observe transient phenomena, and examine unsteady žows. œe development of this technique to obtain both spatial and temporal information about žow Ÿelds is making this apowerful diagnostic tool in žuid mechanics research [4-6]. More recently, using pulsed-laser volume illumination (in place of light sheet illumination), combined with multi-camera capture of particle images in a volumetric region in the žow, has provided the instantaneous velocity vector Ÿeld in the three-dimensional domain [7]. Other approaches to measure global žow velocities come under the category of molecular tagging velocimetry [8] or Doppler global velocimetry [9].