Optimal fluid pumping within confinement by a Giant-Larvacean-inspired undulator

Giant Larvaceans are deep-sea filter-feeding invertebrates that are key contributors to ocean material

transport (Robison et al 2005; Kajita et al 2017), but their tail undulation for effective fluid pumping and

locomotion is still understudied. Direct observations have found non-uniform flexibilities along the tail

and a recent computational model suggested an optimal tissue activation location for downstream fluid

transport (Hoover et al 2021). To experimentally investigate the benefit of an anguilliform undulator

with flexible trailing edge attachments, we build a robot to parametrically varied the attachment size,

flexural rigidity, undulation speed, fluid channel depth, etc. Preliminary results have shown that fluid

pumping has strong correlations with the tail property and undulation speed and a rather weak

correlation with the fluid channel depth. To further understand the coupling of active undulation and

passive tail movement, Euler-Bernoulli Beam theory is applied to model the kinematics of the propulsor,

whereas volumetric flux, vorticity, and Lagrangian Coherent Structures are examined to understand the

dynamics of the cyclic fluid motion. Dimensionless numbers including Keulegan-Carpenter number,

Reynolds number, and reduced frequency are computed to identify the optimal kinematic and fluid

regimes for pumping effectiveness. Our results are compared with similar modes of flexible flappers

(Quinn et al 2014; Fernandez-Prats et al 2015) for commonalities and differences.