Collaborative Research: Experimental Studies to Reveal the Boundary Layer Control Mechanisms of Shark Skin

MOTTA 0932026这项实验工作将研究一种新的、独特的被动边界层分离控制方法，该方法源自鲨鱼皮，在微观水平上发挥作用。鲨鱼的皮肤和牙鳞代表了4亿多年来为提高游泳效率而进行的自然选择。鲨鱼皮肤形态结构的进化适应，以发展独特的边界层控制(BLC)机制，源于随之而来的阻力减少，可能增加鳍性能(如推力产生)和提高快速游泳鲨鱼的转弯敏捷性。之前的研究已经得到了PI的确认，表明鲨鱼的牙齿可以竖起刷毛。PI发现，毛茸茸的微几何形状导致形成了一个相互关联的嵌入腔体的涡系。假设了三种机制，通过阻止鲨鱼皮上的分离来实现边界层控制。第一种机制是形成嵌入的微涡，由于外边界层流动的部分滑移条件，嵌入的微涡增加了非常近壁区的动量。第二种机制是，表面几何结构中固有的优先流动方向抑制了全局流动逆转。第三种机制发生在过渡和湍流边界层条件下，涉及到与空腔的流动交换导致湍流增强，或对近壁区域和空腔中的流动进行额外的激励。这项研究涉及工程师和生物学家共同努力，以全面了解鲨鱼牙齿的形态刷毛机制。这项研究将首次全面描述导致牙齿刷毛的形态机制，并对刷毛的范围和程度(或角度)进行分类，为建立用于水动力测试的鲨鱼皮肤模型提供数据。这三种被动BLC机制将通过流动显示和使用时间分辨数字粒子图像测速仪(tr-DPIV)进行测量来评估。BLC领域的创新需要提供有效的方法来减少阻力(从而增加有效载荷、航程或节省燃料)，改善操纵面的性能，并增强现代技术(如潜艇、飞机)的转弯敏捷性。结果的传播将在期刊/会议记录和公共媒体(如加拿大探索频道)上进行。本科生的参与将通过参与两个NSF REU项目(阿拉巴马大学和Mote海洋实验室)进行，重点是让代表不足的群体参与；REU还将寻求补充，以吸引更多代表不足的本科生。最后，这项研究的结果将由共同的PI纳入Mote海洋实验室关于鲨鱼的教育推广计划/展品，并由PI纳入位于亚利桑那州伯明翰的McWane科学中心的教育推广计划/展览。仅通过这两个渠道的宣传活动，每年就可以教育超过70万人了解鲨鱼皮的减阻特性。

Motta 0932026 This experimental work will study a new and unique passive boundary-layer separation control methodology derived from shark skin, functioning at the micro-scale level. The skin and denticles (scales) of sharks represent over 400 million years of natural selection for swimming efficiency. Evolutionary adaptations in the morphological structure of the shark skin, to develop unique boundary layer control (BLC) mechanisms, stem from the ensuing decrease in drag, probable increase in fin performance (e.g. thrust production) and enhanced turning agility for fast-swimming sharks. Previous work, confirmed by the PIs, has shown the capability for shark denticles to bristle. The PI discovered that a bristled microgeometry results in the formation of a system of interlocking embedded cavity vortices. Three mechanisms are hypothesized which lead to boundary layer control via deterrence of separation over the shark skin. The first mechanism is the formation of embedded micro-vortices that increase momentum in the very near-wall region due to the partial slip condition resulting on the outer boundary layer flow. The second mechanism is that the preferential flow direction inherent in the surface geometry inhibits global flow reversal. The third mechanism, occurring during transitioning and turbulent boundary layer conditions, involves an exchange of flow with the cavities resulting in turbulence augmentation, or an additional energizing of flow in the near-wall region and cavities. The study involves engineers, working together with biologists, to fully comprehend the morphological bristling mechanism of shark denticles. This study will provide the first comprehensive characterization of the morphological mechanism resulting in denticle bristling and will classify the scope and degree (or angle) of bristling, yielding data for the building of shark skin models for hydrodynamic testing. The three passive BLC mechanisms will be evaluated through flow visualization and measurement using Time-Resolved Digital Particle Image Velocimetry (TR-DPIV). Innovations in the field of BLC are needed to provide efficient methodologies to decrease drag (resulting in increased payload, range or fuel savings), improve performance of control surfaces and enhance turning agility of modern technologies (e.g., submarines, aircraft). Dissemination of results will occur in journals/conference proceedings and the public media (e.g. Discovery Channel Canada). Undergraduate student involvement will take place through participation with two NSF REU programs (University of Alabama and Mote Marine Laboratory) with a focus on involving underrepresented groups; an REU supplement will also be sought to involve additional underrepresented undergraduates. Finally, the results from this research will be incorporated into educational outreach programs/exhibits at the Mote Marine Laboratory on sharks by the co-PIs and at the McWane Science Center in Birmingham, AL by the PI. Outreach through these two outlets alone should educate over 700,000 people each year about the drag-reducing properties of shark skin.