Effect of aspect ratio on the propulsive performance of tandem flapping foils

TL;DR

This study investigates how the aspect ratio of tandem flapping foils affects thrust, efficiency, and wake interactions, revealing that higher aspect ratios improve thrust but have limited impact on efficiency, informing biomimetic propulsion design.

Contribution

The paper provides new insights into the influence of aspect ratio on tandem flapping foils through 3D simulations, highlighting the effects on thrust and wake dynamics.

Findings

Higher aspect ratio improves thrust coefficients.

Thrust augmentation benefits level off at high AR.

Propulsive efficiency remains largely unaffected by AR.

Abstract

In this work, we describe the impact of aspect ratio (AR) on the performance of optimally phased, identical flapping flippers in a tandem configuration. Three-dimensional simulations are performed for seven sets of single and tandem finite foils at a moderate Reynolds number, with thrust producing, heave-to-pitch coupled kinematics. Increasing slenderness (or aspect ratio - AR) is found to improve thrust coefficients and thrust augmentation but the benefits level off towards higher values of AR. On the other hand, the propulsive efficiency shows no significant change with increasing AR, while the hind foil outperforms the single by a small margin. Further analysis of the spanwise development and propagation of vortical structures allows us to gain some insights on the mechanisms of these wake interactions and provide valuable information for the design of novel biomimetic propulsion systems.