Abstract：
This smooth flat experimental study investigates the capability of mako shark scales to control flow separation when placed downstream of the onset of turbulent boundary layer separation and within the reattachment region. The objective of the study is to validate the hypothesis that the shark scales\' bristling and recoiling would prevent the flow separation on the flank region (the fastest flow region) of the shark. A rotating cylinder was used to induce an adverse pressure gradient over a flat plate to produce a region of separated flow where the shark skin specimen was mounted. Two types of mako shark scales (flank (B2) and between flank and dorsal fin (B1)) were positioned in the preferred flow direction on a flat plate. The B2 scales are slender, 200μm tall, and can bristle up to 50°. In contrast, B1 scales are wider, shorter, and can bristle at 30°. The bristling angle and shape are the main mechanisms by which the scales act to inhibit flow from moving upstream near the wall. Thus, the difference in the bristling angles and structures of the scales is attributed to the fact that the B2 scales function in a thicker boundary layer (behind the shark\'s gills) where they must bristle sufficiently high into the boundary layer to control the flow separation, and because the adverse pressure gradient in this region is higher where flow separation is more likely. The scales are placed in the reattachment region to elucidate their ability to control and reattach an already separated turbulent flow. The results show that B2 scales placed in the reattachment region reduce the size of the turbulent separation bubble and decrease the turbulent kinetic energy, while B1 scales have the opposite effect.
摘要：
这项光滑平坦的实验研究研究了当放置在湍流边界层分离开始的下游和再附着区域内时，马科鲨鱼鳞片控制流动分离的能力。该研究的目的是验证以下假设：鲨鱼鳞片的刚毛和反冲会阻止鲨鱼侧翼区域（最快流动区域）上的流动分离。使用旋转圆柱体在平板上引起不利的压力梯度，以产生分离的流动区域，其中安装了鲨鱼皮样本。两种类型的mako鲨鱼鳞片（侧翼（B2）以及侧翼和背鳍之间（B1））沿优选的流动方向放置在平板上。B2的刻度是细长的，200μm高,并且可以刷毛高达50°。相比之下,B1尺度更宽，更短，并且可以在30º处硬毛。刷毛的角度和形状是主要机制，通过这些机制，鳞片可以阻止水流在壁附近向上游移动。因此，鳞片的刷毛角度和结构的差异归因于以下事实：B2鳞片在较厚的边界层（鲨鱼g后面）起作用，它们必须在足够高的位置进入边界层以控制流动分离，并且因为该区域中的不利压力梯度较高，其中流动分离更可能。将鳞片放置在重新附着区域中，以阐明其控制和重新附着已经分离的湍流的能力。结果表明，B2鳞片放置在再附着区减小了湍流分离气泡的尺寸，降低了湍流动能，而B1量表则有相反的效果。
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