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haru007

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[交流] 【求助】求助有关润滑剂的英文翻译[b]（已到期）[/b]

本人硕士期间不是做这个方向的，对此一窍不通，就连文章名我也翻译不明白，可是博士复试需要讲述英文文献
所以请高手帮忙
Drag Reduction on a Patterned Superhydrophobic Surface必有重谢！
截至日期2009.05.02

We present an experimental study of a low-Reynolds number shear flow between two surfaces, one of
which has a regular grooved texture augmented with a superhydrophobic coating. The combination
reduces the effective fluid-surface contact area, thereby appreciably decreasing the drag on the surface and
effectively changing the macroscopic boundary condition on the surface from no slip to limited slip. We
measure the force on the surface and the velocity field in the immediate vicinity on the surface (and thus
the wall shear) simultaneously. The latter facilitates a direct assessment of the effective slip length
associated with the drag reduction.

On the boundary between a viscous fluid and a solid
surface the fluid velocity with respect to the surface is
generally assumed to be zero (no-slip condition), and the
amount of experience verifying this assumption is massive.
From molecular dynamics considerations, while slip may
occur on the boundary, its effects should be confined to the
nanoscale realm. This notion is also well supported by
experimental results [1,2]. Thus it is inevitable that in
any fluid flow, one has to deal with shear caused by the
difference between the free-stream velocity and the zero
boundary velocity. This shear is the reason for the drag
force on any body moving through fluid and for the pressure
drop in any internal flow. The practical motivation to
reduce the drag and the pressure drop is great, but is there
anything that can be done?
In turbulent flows, a large fraction of the drag is produced
by intermittent coherent structures. The energy dissipation
by these structures can be reduced [3,4] by
smoothing (laminarizing) the flow field. The next question
that arises is if the laminar drag can be decreased without
changing the macroscopic flow parameters (free-stream
fluid properties, body size, geometry and surface temperature,
etc.). Recent works [5–7] report evidence of such
drag decrease obtained by reducing the effective contact
area between the solid and the fluid. The fundamental
importance of such flows over soft or patterned surfaces
has been recently emphasized [8].
The contact area minimization was made possible by the
development of superhydrophobic (SH) coatings. These
coatings greatly decrease the energy of the interaction
between the surface and the fluid, leading to unusually
high contact angles for drops resting on SH surfaces [9].
If the solid surface is textured, with a regular or irregular
pattern, a regime may emerge where there is insufficient
energy to deform the fluid interface to bring it in contact
with the entire solid surface [Cassie regime [9] ], resulting
in voids forming in the recessed parts of the pattern. For the
parts of the fluid interface above the voids, the no-slip
boundary condition will be no longer applicable, and the
simplest boundary-condition assumption for these parts
will be free slip (no shear on the interface), although in
reality there still may be some small drag transmitted to the
no-contact patches by the gas filling the voids. For a regular
pattern of recessed grooves (free-slip) and protruding lands
(no-slip), both analytical [10] and numerical [7,10] solutions
show the drag to decrease with the characteristic size
of the recessed surface features. As the feature size becomes
larger, however, the fluid once again will come into
contact with the recessed parts of the pattern, thus limiting
the scale range of surface features that result in sliplike
behavior.
While the feature sizes characteristic of the SH coating
itself are usually on a submicron scale, voids can be greatly
increased in size if the SH coating is applied to a textured
surface [6,7] with features on the scale from microns to
tens of microns, thereby producing a measurable change in
the pressure drop [6] in an internal flow, in the terminal
velocity of a drop rolling down the surface [7], or in the
drag coefficient in an external flow [7]. It has been stipulated
that, while there is no slip on the microscopic scale,
the macroscopic boundary condition for the tangential
velocity component u near a textured SH surface can be
interpreted as Navier slip [11], with the slip velocity at the
wall us proportional to the shear: us b@u=@y. The
direction y is normal to the wall, and the dimensional
coefficient b is the slip length.
In this Letter, we present flow measurements near a
regularly textured SH surface in shear flow showing macroscopic
effective [12] [or apparent [8,12] ] slip leading to
drag reduction on the order of 20%. Moreover, the observed
results cannot be entirely explained by the reduction
of drag due solely to the formation of slip areas above the
grooves in the pattern, suggesting that additional dynamic
effects [e.g., related to nanobubble formation [13] ] may
play a role, as discussed below. In our experiment, reliable
optical measurements are taken simultaneously with
torque measurements. With the former, we measure the
velocity field and extract the liquid-solid interface stress.
The latter provide a direct measurement of the stress.
Knowing the difference between the actual measured stress

特别是涂红的，什么意思啊?

请大家帮忙

[ Last edited by haru007 on 2009-5-15 at 09:51 ]

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