This experimental investigation discusses the effectiveness of shortfin mako shark skin to passively control turbulent boundary layer separation. Experiments were conducted in a water tunnel facility with the shark skin specimens mounted on a smooth flat plate subjected to an adverse pressure gradient. The two skin specimens have shark scales with different sizes, shapes, and bristling angles. The flank region scales (B2) are slender, tall, and can bristle at 50°, while the scales in the region between flank and dorsal fin (B1) are wide, short, and can bristle at 30°. The adverse pressure gradient on the plate was generated by a rotating cylinder. DPIV measurements indicate that unpainted scales B2 can fully control or delay boundary layer separation and reduce the fraction of time the flow is reversed. The bristling of the scales caused fluctuation in the skin friction curve and the single spike intensity of the normal stress very close to the wall. These capabilities are directly related to the scale bristling angle. In contrast, the low bristling angle of the scales from region B1 did not impede the reversing flow, and therefore separation was enhanced. The increase in Reynold’s stress fluctuations away from the wall indicated that the separation region increased in size due to vortex structures further from the wall. Once the bristling mechanism of the B2 scales was eliminated by painting over the skin, the scales functioned as a rough surface but still promoted separation delay. In addition, the streamwise Reynolds stress profile for the flow over the painted scales measured after separation occurred, along with the high intensity of the normal stress near the surface are both characteristics of a flow over a rough surface. In summary, the shark skin surface showed an ability to both delay and increase flow separation depending on the capabilities of the scale bristling to inhibit reversing flow.

这项实验研究讨论了短鳍真鲨鲨鱼皮被动控制湍流边界层分离的有效性。实验是在水隧道设施中进行的，将鲨鱼皮标本安装在承受不利压力梯度的光滑平板上。这两个皮肤样本的鲨鱼鳞片大小，形状和刷毛角度都不同。侧面的鳞片（B2）细长，高，并且在50°处可以刷毛，而在侧面和背鳍之间的区域（B1）的鳞片宽，短并且可以在30°处刷毛。板上的不利压力梯度是由旋转的圆柱体产生的。DPIV测量表明，未上漆的水垢B2可以完全控制或延迟边界层的分离，并减少流动逆转的时间。鳞片的刺毛引起皮肤摩擦曲线的波动，并且正应力的单尖峰强度非常靠近壁。这些功能与刻度尺的硬毛角度直接相关。相反，来自区域B1的水垢的低刷毛角没有阻碍反向流动，因此分离得到增强。远离壁的雷诺应力波动的增加表明，分离区域的尺寸由于远离壁的涡旋结构而增大。通过在皮肤上涂漆消除了B2鳞片的刚毛机理，这些鳞片起着粗糙的表面的作用，但仍促进了分离的延迟。此外，在分离发生后，在涂漆鳞片上测量的水流的流向雷诺应力分布图，以及表面附近法向应力的高强度都是在粗糙表面上流动的特征。总之，鲨鱼皮表面显示出延迟和增加水流分离的能力，这取决于水垢硬毛抑制逆流的能力。