Thomas, P. J. (Peter J.), Zoueshtiagh, F., Merlen, A. and Thomy, V. (2008) Micro ripples, sand ripples and their universal wavelength scaling. In: The 7th EUROMECH Fluid Mechanics Conference, University of Manchester, Manchester, U.K., Sep 14-18, 2008. Published in: EFMC7 Book of Abstracts p. 326.

Abstract

Results from experiments investigating oscillatory motion of a fluid carrying suspended micron-sized particles in a capillary tube (diameter: 288Pm) are summarized - the experimental set up is illustrated in Fig. 1. The oscillatory fluid motion is driven by a computer-controlled syringe pump and filmed with two video cameras A and B; for details refer to Ref. 1. The experiments show that initially uniformly distributed particles can segregate and accumulate to form regularly spaced micron-sized particle clusters within the capillary tube (Fig. 2). As far as we are aware these represent the smallest ripple structures that have hitherto been reported. The wavelength of the micro clusters is compared to wavelength data for macroscopic sand-ripple patterns from the literature for studies conducted over a wide range of substantially different experimental conditions. It is found that the wavelength of the micro ripples follows the same universal scaling that was obtained in Ref. 2 for the wavelength of the macroscopic sand-ripple patterns. This agreement of the scaling suggests that relevant local scales on the surface of the granular layer, where the ripples form, govern the ripple-formation mechanism. Hence, all global scales and global flow features are irrelevant. Prompted by this conclusion a dimensional and asymptotic analysis is performed1 yielding a power-law scaling exponent that agrees to within 4% with that found in Ref. 2 from experimental data. This very good agreement theoretically supports the universality of the scaling obtained in Ref. 2 on a purely experimental basis.

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