Laser Doppler anemometry measurements in an index of refraction matched column in the presence of dispersed beads - Part I

Laser Doppler anemometry was used to measure axial and radial velocity comp onents in a liquid flow field in the presence of dispersed beads. Index of refraction matching between the fluid (para-cymene) and large, spherical be ads, made of polymethyl methacrylate, was essential to extract the turbulen ce data from the fluid phase because of the high concentration of beads. Th e match allowed measurements without generating noise from the surface of t he beads. The measurements were obtained under transient flow conditions to avoided need for an external solids circulation loop. The resulting data w ere statistical and ensembled averaged for short periods during the transie nt experiments where the concentration could be taken as approximately cons tant. The concentration levels were determined from separate particle track ing velocimetry measurements, to be described in Part II. The bead density was greater than the fluid and thus wakes were created. These local areas o f fluid experienced a lowering of the velocity. The turbulent fluctuation r esults showed that the presence of the beads extracted energy from the mean flow and transferred that energy to the turbulence. The increase of turbul ent intensity was impressive along the centerline of the column where the m easurements were made. The axial turbulent intensity of the fluid without b eads was of the order of 10% and with heads, the level was increased to nea rly 70%. (C) 2000 Elsevier Science Ltd. All rights reserved.