Flow analysis of the low-Reynolds number swimmer C. elegans

TL;DR

This study combines experimental and numerical methods to analyze the flow fields around the swimming nematode C. elegans at low Reynolds numbers, revealing the importance of three-dimensional effects for accurate flow measurement.

Contribution

The paper introduces a combined experimental and numerical approach to accurately analyze low-Reynolds number flow fields around C. elegans, highlighting the significance of out-of-plane contributions.

Findings

Planar flow measurements underestimate true shear rates.

Numerical simulations agree well with experimental data.

Out-of-plane effects can be inferred from in-plane data using incompressibility.

Abstract

Swimming cells and microorganisms are a critical component of many biological processes. In order to better interpret experimental studies of low Reynolds number swimming, we combine experimental and numerical methods to perform an analysis of the flow-field around the swimming nematode Caenorhabditis elegans. We first use image processing and particle tracking velocimetry to extract the body shape, kinematics, and flow-fields around the nematode. We then construct a three-dimensional model using the experimental swimming kinematics and employ a boundary element method to simulate flow-fields, obtaining very good quantitative agreement with experiment. We use this numerical model to show that calculation of flow shear rates using purely planar data results in significant underestimates of the true three-dimensional value. Applying symmetry arguments, validated against numerics, we demonstrate that the out-of-plane contribution can be accounted for via incompressibility and therefore simply calculated from particle tracking velocimetry. Our results show how fundamental fluid mechanics considerations may be used to improve the accuracy of measurements in biofluiddynamics.