交换水流研究

Understanding how the hydrodynamics of feeding, nutrient and gas exchange is affected by the morphology and orientation of jellyfish is important to distinguish their individual mechanisms of foraging. The differences between the currents generated by oblate medusa that rest on the ocean floor and the more commonly observed free-swimming medusa have previously not been explored. The pulsing kinematics and fluid flow around the upside-down jellyfish, Cassiopea spp., contained in laboratory aquaria is experimentally investigated using a combination of videography and digital particle image velocimetry measurements. The phase-averaged flow generated by bell pulsations is similar to a vertical jet, with induced flow velocities on the order of 1-10 mm/s. The bell margin is pushed downward during full contraction in a manner not previously observed in free-swimming medusae kinematics, due to the fact that the Cassiopea bell rests against a solid surface. This introduces a strong near-horizontal entrainment of the fluid toward the oral arms unlike the mostly upstream entrainment observed in free-swimming medusae. There is no evidence of the formation of a train of vortex rings as observed in oblate medusae exhibiting rowing propulsion. This is primarily due to the difference in the morphology of Cassiopea in which the oral arms extend to radial lengths greater than the maximum bell diameter. The resulting net fluid motion is not dominated by flow-reversal regions, suggesting that Cassiopea brings in new fluid with each bell pulse for the purposes of filter feeding, oxygen exchange and excretion.

注射磷脂后，表面张力随时间缓慢下降；磷脂吸附在界面上。交换水相会停止磷脂的吸附，只有液滴表面积的变化才能改变磷脂单层的表面浓度和表面压力。

本文介绍了浅水流动表面的大尺度PIV测量方法，详细介绍了实验设备和不用激光照明进行PIV测量的技术途径。特别研究了在表面流动分析时示踪粒子的选择和播撒方法。