MULTIPLE LIGHT-SCATTERING IN TAYLOR-COUETTE FLOW

Authors
Citation
D. Bicout et G. Maret, MULTIPLE LIGHT-SCATTERING IN TAYLOR-COUETTE FLOW, Physica. A, 210(1-2), 1994, pp. 87-112
Citations number
29
Categorie Soggetti
Physics
Journal title
ISSN journal
03784371
Volume
210
Issue
1-2
Year of publication
1994
Pages
87 - 112
Database
ISI
SICI code
0378-4371(1994)210:1-2<87:MLITF>2.0.ZU;2-E
Abstract
We report dynamic light scattering experiments on turbid colloidal sus pension under stationary and laminar flow, as well as in the regime of flow instabilities. It is shown that the time autocorrelation functio n C1(t) = [E(0)E(t)]/[\ E(0)\ 2] of the scattered light field E(t) is not sensitive to the mean velocity flow but rather to the root mean s quare of velocity gradient. C1(t) is characterised on the level of eac h scattering event by the correlation time required by a pair of scatt erers initially separated by a transport mean free path to move a rela tive distance of optical wavelength due to the velocity gradient. We v erified this theoretical analysis using planar Couette flow as an exam ple for homogeneous velocity gradients, and planar Poiseuille flow for inhomogeneous velocity gradients. Agreement between experiment and th eory is excellent. Finally, this technique is applied to spatially var ying velocity gradient fields for measuring the threshold and wave num ber of the Taylor-Couette instability. This illustrates the possibilit y of studying hydrodynamic instabilities and quasi-local velocity grad ients even under conditions of strong multiple scattering.