COLLECTIVE LIGHT-SCATTERING AND INSTANTANEOUS FLUID VELOCITY-MEASUREMENT

Collective Light Scattering (CLS) from gas density irregularities is a nalysed using electromagnetic theory and fluid mechanics. The scattere d signal is shown to provide three decisive pieces of information: (1) the signal frequency spectrum gives the Doppler shifted velocity prob ability distribution; (2) new processing of the modulus and phase spec tra of the complex signal provides the velocity fluctuations frequency spectrum; (3) appropriate filtering of the signal phase time derivati ve provides the real time instantaneous convection velocity. This info rmation illustrated and extracted from CLS signals obtained in a turbu lent mixing layer experiment. (C) 1996 Published by Elsevier Science L td.