How shape and flapping rate affect the distribution of fluid forces on flexible hydrofoils

TL;DR

This study explores how the shape and flapping rate of flexible hydrofoils influence the distribution of fluid forces, using advanced pressure measurement and flow visualization techniques to understand propulsion and internal stresses.

Contribution

It introduces a high-resolution method to map fluid forces on deforming hydrofoils and analyzes the effects of geometry and flapping frequency on propulsion efficiency.

Findings

Force distribution varies significantly with fin shape and flapping rate.

Hydrodynamic forces correlate with propulsive thrust and internal tension.

Advanced pressure and flow measurement techniques enable detailed force mapping.

Abstract

We address the fluid-structure interaction of flexible fin models oscillated in a water flow. Here, we investigate in particular the dependence of hydrodynamic force distributions on fin geometry and flapping frequency. For this purpose, we employ state-of-the-art techniques in pressure evaluation to describe fluid force maps with high temporal and spatial resolution on the deforming surfaces of the hydrofoils. Particle tracking velocimetry (PTV) is used to measure the 3D fluid velocity field, and the hydrodynamic stress tensor is subsequently calculated based on the Navier-Stokes equation. The shape and kinematics of the fin-like foils are linked to their ability to generate propulsive thrust efficiently, as well as the accumulation of external contact forces and the resulting internal tension throughout a flapping cycle.