Bartol Ian K, Gharib Morteza, Webb Paul W, Weihs Daniel, Gordon Malcolm S
Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529-0266, USA.
J Exp Biol. 2005 Jan;208(Pt 2):327-44. doi: 10.1242/jeb.01356.
Boxfishes (Teleostei: Ostraciidae) are marine fishes having rigid carapaces that vary significantly among taxa in their shapes and structural ornamentation. We showed previously that the keels of the carapace of one species of tropical boxfish, the smooth trunkfish, produce leading edge vortices (LEVs) capable of generating self-correcting trimming forces during swimming. In this paper we show that other tropical boxfishes with different carapace shapes have similar capabilities. We conducted a quantitative study of flows around the carapaces of three morphologically distinct boxfishes (spotted boxfish, scrawled cowfish and buffalo trunkfish) using stereolithographic models and three separate but interrelated analytical approaches: digital particle image velocimetry (DPIV), pressure distribution measurements, and force balance measurements. The ventral keels of all three forms produced LEVs that grew in circulation along the bodies, resembling the LEVs produced around delta-winged aircraft. These spiral vortices formed above the keels and increased in circulation as pitch angle became more positive, and formed below the keels and increased in circulation as pitch angle became more negative. Vortices also formed along the eye ridges of all boxfishes. In the spotted boxfish, which is largely trapezoidal in cross section, consistent dorsal vortex growth posterior to the eye ridge was also present. When all three boxfishes were positioned at various yaw angles, regions of strongest concentrated vorticity formed in far-field locations of the carapace compared with near-field areas, and vortex circulation was greatest posterior to the center of mass. In general, regions of localized low pressure correlated well with regions of attached, concentrated vorticity, especially around the ventral keels. Although other features of the carapace also affect flow patterns and pressure distributions in different ways, the integrated effects of the flows were consistent for all forms: they produce trimming self-correcting forces, which we measured directly using the force balance. These data together with previous work on smooth trunkfish indicate that body-induced vortical flows are a common mechanism that is probably significant for trim control in all species of tropical boxfishes.
箱鲀（硬骨鱼纲：箱鲀科）是一种海洋鱼类，其坚硬的甲壳在不同分类单元中的形状和结构装饰差异很大。我们之前表明，一种热带箱鲀——光滑多板盾尾鱼的甲壳龙骨会产生前缘涡流（LEV），在游泳时能够产生自我修正的平衡力。在本文中，我们表明其他具有不同甲壳形状的热带箱鲀也有类似的能力。我们使用立体光刻模型和三种独立但相互关联的分析方法，对三种形态不同的箱鲀（花斑箱鲀、瘤背鼻鱼和水牛多板盾尾鱼）的甲壳周围流动进行了定量研究：数字粒子图像测速技术（DPIV）、压力分布测量和力平衡测量。所有这三种形态的腹侧龙骨都产生了前缘涡流，这些涡流沿着身体循环增长，类似于三角翼飞机周围产生的前缘涡流。这些螺旋涡流在龙骨上方形成，并随着俯仰角变得更正而循环增加，在龙骨下方形成，并随着俯仰角变得更负而循环增加。所有箱鲀的眼嵴周围也形成了涡流。在横截面大致为梯形的花斑箱鲀中，眼嵴后方还存在持续的背侧涡流增长。当所有三种箱鲀处于不同的偏航角时，与近场区域相比，甲壳远场位置形成了最强的集中涡度区域，并且涡旋循环在质心后方最大。一般来说，局部低压区域与附着的集中涡度区域相关性良好，尤其是在腹侧龙骨周围。尽管甲壳的其他特征也以不同方式影响流动模式和压力分布，但所有形态的流动综合效应是一致的：它们产生平衡自我修正力，我们使用力平衡直接测量了这些力。这些数据以及之前关于光滑多板盾尾鱼的研究表明，身体诱导的涡旋流动是一种常见机制，可能对所有热带箱鲀物种的平衡控制都很重要。
