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haru007木虫 (著名写手)
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【求助】求助有关润滑剂的英文翻译[b]（已到期）[/b]
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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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wangzhuo9736
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2楼2009-06-12 14:30:50
guangguang_1983
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haru007(金币+1,VIP+0):谢谢！！谢谢支持！ 6-12 14:33
haru007(金币+9,VIP+0): 6-12 14:36
haru007(金币+1,VIP+0):谢谢！！谢谢支持！ 6-12 14:33
haru007(金币+9,VIP+0): 6-12 14:36
同意楼上的翻译！ |
3楼2009-06-12 14:32:24
