A Pitching Foil with a Flexible flap Creates an Orderly Jet

TL;DR

This study experimentally demonstrates that a pitching foil with an optimally flexible flap generates a coherent, narrow jet and thrust in quiescent fluid, contrasting with the weak, divergent jet from a rigid foil.

Contribution

It introduces the effect of flap flexibility on jet formation in pitching foils, highlighting how proper flexibility creates an orderly jet and enhances thrust.

Findings

Flexible flap produces a coherent, narrow jet

Rigid foil produces a weak, divergent jet

Optimal flexibility is key for orderly jet formation

Abstract

We experimentally studied the effect of flexibility on the flow produced by sinusoidally pitching foil in quiescent fluid. The rigid foil produces a weak, divergent and meandering jet. On the contrary, the foil with a flexible flap produces an orderly, narrow, coherent jet. It has been observed that such orderly jet is produced when the flap has appropriate flexibility. The jet produced in quiescent fluid by the flexible foil is accompanied by a corresponding thrust. In that sense, this is simple and different type of hovering.