Marine crustaceans with hairy appendages: role of hydrodynamic boundary layers in sensing and feeding

TL;DR

This study investigates how decapod crustaceans use hairy appendages to sense and feed by manipulating flow and boundary layers, revealing a new transitional flow phase and developing a predictive model.

Contribution

The paper introduces a new flow phase called deflection and presents a boundary layer-based model that predicts flow behavior around hairy appendages with no fitting parameters.

Findings

Identification of a third flow phase: deflection.

A boundary layer model accurately predicts flow phases.

Model aligns with experimental data and crustacean measurements.

Abstract

Decapod crustaceans have appendages with an array of rigid hairs covered in chemo-receptors, used to sense and track food. Crustaceans directly influence the flow behavior by changing the speed of flow past the hairy surface, thereby manipulating the Reynolds number (Re). Hairs act either as a rake - diverting flow around the hair array, or as a sieve - filtering flow through the hairs. In our experiments, we uncover a third transitional phase: deflection - where the flow partially penetrates the hair array and is deflected laterally. We develop a reduced order model that predicts the flow phase based on the depth of the boundary layer on a single hair. This model with no fitting parameters agrees very well with our experimental data. Additionally, our model agrees well with measurements of both chemo-sensing and suspension-feeding crustaceans, and can be generalized for many different geometries.