Mechanical & Materials Engineering, Department of


Date of this Version

Winter 12-8-2014


Zhou, J., Evaluation of the Mass Transfer Effect of the Stalk Contraction-Relaxation Cycle of Vorticella Convallaria, 2014, University of Nebraska-Lincoln, NE.


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Mechanical Engineering and Applied Mechanics, Under the Supervision of Professor Sangjin Ryu. Lincoln, Nebraska: December 2014

Copyright (c) 2014 Jiazhong Zhou


Vorticella convallaria is a genus of protozoa living in fresh water. It has a bell-shaped zooid equipped with adoral ciliary bands and a contractile stalk tethering the zooid to a substrate. Vorticella is regarded as a biological spring because its contractile stalk can pull the zooid towards the substrate at a remarkably high speed and then relaxes to its extended state much more slowly. However, reasons for Vorticella’s stalk contraction are still unknown. It is presumed that the flow field induced by the contraction-relaxation cycle of Vorticella would augment mass transfer effect near the substrate. We investigated this hypothesis with an experimental Vorticella model with particle tracking velocimetry and a computational fluid dynamics model. In both approaches, Vorticella is modeled as a solid sphere translating perpendicular to a solid surface in water. After having been validated by the experimental model and verified by grid convergence index test, the computational model simulated water flow caused by Vorticella during the cycle, based on the measured time course of stalk length changes of Vorticella. We calculated the trajectory of particles, which were uniformly distributed near Vorticella initially, based on the simulated flow field, and then evaluated the mass transfer effect of Vorticella’s stalk contraction-relaxation by spatial point analysis. The results illustrated that the uniformly distributed particles were transferred to the area away from the Vorticella radially, and became more clustered against a statistical model of purely random point pattern. The results indicate the mass transfer effect has been enhanced in the vicinity of Vorticella.

Advisor: Sangjin Ryu