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

本实验工作将研究一种新的、独特的基于鲨鱼皮的被动边界层分离控制方法，该方法在微观尺度上起作用。鲨鱼的皮肤和牙齿（鳞片）代表了4亿多年来对游泳效率的自然选择。鲨鱼皮肤形态结构的进化适应，以发展独特的边界层控制机制，源于随之而来的阻力减少，鳍性能可能增加（例如推力产生），以及快速游动的鲨鱼转向敏捷性增强。先前的研究得到了pi的证实，表明鲨鱼的小齿能够长出刚毛。PI发现，一个刚毛的微观几何结构导致了一个互锁嵌入腔涡系统的形成。本文假设了三种机制，通过对鲨鱼皮分离的威慑来控制边界层。第一种机制是内嵌微涡的形成，由于外边界层流动导致的局部滑移情况，微涡在非常近壁面区域增加了动量。第二个机制是表面几何形状固有的优先流动方向抑制了全球流动逆转。第三种机制发生在过渡和湍流边界层条件下，涉及与空腔的流动交换，导致湍流增强，或近壁区域和空腔的流动额外激活。这项研究包括工程师和生物学家的合作，以充分了解鲨鱼牙的形态机制。该研究将首次全面表征导致小齿刚毛的形态学机制，并将对刚毛的范围和程度（或角度）进行分类，为建立用于水动力测试的鲨鱼皮模型提供数据。三种被动BLC机制将通过流动可视化和使用时间分辨数字粒子图像测速（TR-DPIV）的测量来评估。需要在BLC领域进行创新，以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），改善控制面性能并增强现代技术（例如潜艇，飞机）的转向敏捷性。结果将在期刊/会议论文集和公共媒体（如加拿大探索频道）上传播。本科生将参与两个NSF REU项目（阿拉巴马大学和莫特海洋实验室），重点关注代表性不足的群体；还将寻求一份REU补编，招收更多人数不足的本科生。最后，这项研究的结果将被纳入教育推广计划/展览，由联合PI在莫特海洋实验室和由PI在阿拉巴马州伯明翰的麦克文科学中心举办。仅通过这两个渠道，每年就可以教育70多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.