TY - JOUR

T1 - Measurement and computation of hydrodynamic coupling at an air/water interface with an insoluble monolayer

AU - Hirsa, Amir H.

AU - Lopez, Juan

AU - Miraghaie, Reza

N1 - Copyright:
Copyright 2007 Elsevier B.V., All rights reserved.

PY - 2001/9/25

Y1 - 2001/9/25

N2 - The coupling between a bulk vortical flow and a surfactant-influenced air/water interface has been examined in a canonical flow geometry through experiments and computations. The flow in an annular region bounded by stationary inner and outer cylinders is driven by the constant rotation of the floor and the free surface is initially covered by a uniformly distributed insoluble monolayer. When driven slowly, this geometry is referred to as the deep-channel surface viscometer and the flow is essentially azimuthal. The only interfacial property that affects the flow in this regime is the surface shear viscosity, μs, which is uniform on the surface due to the vanishingly small concentration gradient. However, when operated at higher Reynolds number, secondary flow drives the surfactant film towards the inner cylinder until the Marangoni stress balances the shear stress on the bulk fluid. In general, the flow can be influenced by the surface tension, δ, and the surface dilatational viscosity, Ks, as well as μs. However, because of the small capillary number of the present flow, the effects of surface tension gradients dominate the surface viscosities in the radial stress balance, and the effect of μs can only come through the azimuthal stress. Vitamin K1 was chosen for this study since it forms a well-behaved insoluble monolayer on water and μs is essentially zero in the range of concentration on the surface, c, encountered. Thus the effect of Marangoni elasticity on the interfacial stress could be isolated. The flow near the inteface was measured in an optical channel using digital particle image velocimetry. Steady axisymmetric flow was observed at the nominal Reynolds number of 8500. A numerical model has developed usiong the axisymmetric Navier-Strokes equations to examine the details of the coupling between the bulk and interface. The nonlinear equation of state, δ(c), for the vitamins K1 monolayer between the measurements and in thecomputations. Agreement was demonstrated between the measurements and computations, but the flow is critically dependent on the nonlinear equation of state.

AB - The coupling between a bulk vortical flow and a surfactant-influenced air/water interface has been examined in a canonical flow geometry through experiments and computations. The flow in an annular region bounded by stationary inner and outer cylinders is driven by the constant rotation of the floor and the free surface is initially covered by a uniformly distributed insoluble monolayer. When driven slowly, this geometry is referred to as the deep-channel surface viscometer and the flow is essentially azimuthal. The only interfacial property that affects the flow in this regime is the surface shear viscosity, μs, which is uniform on the surface due to the vanishingly small concentration gradient. However, when operated at higher Reynolds number, secondary flow drives the surfactant film towards the inner cylinder until the Marangoni stress balances the shear stress on the bulk fluid. In general, the flow can be influenced by the surface tension, δ, and the surface dilatational viscosity, Ks, as well as μs. However, because of the small capillary number of the present flow, the effects of surface tension gradients dominate the surface viscosities in the radial stress balance, and the effect of μs can only come through the azimuthal stress. Vitamin K1 was chosen for this study since it forms a well-behaved insoluble monolayer on water and μs is essentially zero in the range of concentration on the surface, c, encountered. Thus the effect of Marangoni elasticity on the interfacial stress could be isolated. The flow near the inteface was measured in an optical channel using digital particle image velocimetry. Steady axisymmetric flow was observed at the nominal Reynolds number of 8500. A numerical model has developed usiong the axisymmetric Navier-Strokes equations to examine the details of the coupling between the bulk and interface. The nonlinear equation of state, δ(c), for the vitamins K1 monolayer between the measurements and in thecomputations. Agreement was demonstrated between the measurements and computations, but the flow is critically dependent on the nonlinear equation of state.

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U2 - 10.1017/S0022112001005262

DO - 10.1017/S0022112001005262

M3 - Article

AN - SCOPUS:0035949771

VL - 443

SP - 271

EP - 292

JO - Journal of Fluid Mechanics

JF - Journal of Fluid Mechanics

SN - 0022-1120

ER -