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Line, profile and boundary layer sensors

Today's commercially available Laser Doppler Anemometers (LDA, LDV) are of the cross beam type. The cross section of both beams is called measuring volume and has an ellipsoidal shape with a length of typically one millimeter and a diameter of 100 μm. For certain flow regions of interest the measuring volume is not small enough, i. e. regions near a surface or in a vortex where large gradients are present. Since decreasing the measuring volume reaches the limits of this principle, the PTB has developed sensors not to measure only velocity but also the associated location of the tracers seeded in the flow. The mapping of velocity and spatial location allows to measure velocity profiles inside the measuring volume. Different LDA set-ups have been developed with a spatial resolution down to the μm-range, with extended measuring volumes up to 100 mm, with a high sensitivity for the diameter of the scattering particles, and with detection of velocity vector profiles. To illustrate the function of profile, line or boundary layer LDAs animations have been created which are presented on the following pages:

 

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