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The appearance of boundary layers and drift flows due to high-frequency surface waves

Published online by Cambridge University Press:  20 July 2012

Ofer Manor
Affiliation:
MicroNanophysics Research Laboratory, School of Electrical and Computer Engineering, RMIT University, Melbourne, VIC 3001, Australia The Melbourne Centre for Nanofabrication, Clayton, VIC 3800, Australia
Leslie Y. Yeo
Affiliation:
MicroNanophysics Research Laboratory, School of Electrical and Computer Engineering, RMIT University, Melbourne, VIC 3001, Australia
James R. Friend*
Affiliation:
MicroNanophysics Research Laboratory, School of Electrical and Computer Engineering, RMIT University, Melbourne, VIC 3001, Australia The Melbourne Centre for Nanofabrication, Clayton, VIC 3800, Australia
*
Email address for correspondence: [email protected]

Abstract

The classical Schlichting boundary layer theory is extended to account for the excitation of generalized surface waves in the frequency and velocity amplitude range commonly used in microfluidic applications, including Rayleigh and Sezawa surface waves and Lamb, flexural and surface-skimming bulk waves. These waves possess longitudinal and transverse displacements of similar magnitude along the boundary, often spatiotemporally out of phase, giving rise to a periodic flow shown to consist of a superposition of classical Schlichting streaming and uniaxial flow that have no net influence on the flow over a long period of time. Correcting the velocity field for weak but significant inertial effects results in a non-vanishing steady component, a drift flow, itself sensitive to both the amplitude and phase (prograde or retrograde) of the surface acoustic wave propagating along the boundary. We validate the proposed theory with experimental observations of colloidal pattern assembly in microchannels filled with dilute particle suspensions to show the complexity of the boundary layer, and suggest an asymptotic slip boundary condition for bulk flow in microfluidic applications that are actuated by surface waves.

Type
Papers
Copyright
Copyright © Cambridge University Press 2012

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