Yu.N. Dubnishchev
Institute of Thermophysics, Siberisn Branch, Russian Academy of Sciences, Russia

Multiparticle sckattering problem in laser doppler anemometry

The effect of multiparticle scattering and possibility to minimize it in the basic schemes Laser Doppler Anemometry (LDA) and Doppler Global Velocimetry (DGV) are discussed. It is shown that this effect takes place in heterodyne and differential schemes LDA. It is minimized when the medium has no velocity gradients of scattering particles. In the Rayleigh scheme the multiparticle scattering effect on the result of measurements of the Doppler frequency shift can be neglected, since it is reduced to the amplitude noice in a narrowband signal. In DGV the effect of multiparticle scattering is eliminated by obtining differential combinations of frequency–demodulated images of the laser sheet in different regions of the angular spectrum of scattered light. In case of DGV for 3D velocity vector may be used single CCD–camera. The coordinate measuring basis is formed due to switching of the directions and the frequency of spatially combined laser sheets, the frequency being synchronized with the CCD–camera operation. The field of the velocity vectors without the contribution from the multiparticle scattering is produced from the linear combinations of normalized laser sheet images detected with a CCD–camera in a frequency–demodulated scattered light.
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