Large-amplitude undulatory swimming near a wall

TL;DR

This experimental study investigates how a flexible undulating foil's swimming performance near a wall is affected, revealing that walls can significantly enhance speed and thrust through vorticity dynamics and flow energy modes.

Contribution

The paper provides new experimental insights into the effects of walls on undulatory swimming, including detailed flow analysis using PIV and POD techniques.

Findings

Wall presence increases cruising velocity up to 25%

Thrust can be enhanced by 45% near a wall

Vorticity dynamics explain the propulsion enhancement

Abstract

The propulsive dynamics of a flexible undulating foil in a self-propelled swimming configuration near a wall is studied experimentally. Measurements of the swimming speed and the propulsive force are presented, together with image acquisition of the kinematics of the foil and particle image velocimetry (PIV) in its wake. The presence of the wall enhances the cruising velocity in some cases up to 25% and the thrust by a 45%, for swept angles of 160 and 240 degrees. The physical mechanisms underlying this effect are discussed by studying the vorticity dynamics in the wake of the foil. Proper Orthogonal Decomposition (POD) is applied to the PIV measurements in order to analyse the kinetic energy modal distribution in the flow and to relate it to the propulsion generated by the foil.