Biomimetic bluff body drag reduction by self-adaptive porous flaps

TL;DR

This study introduces a biomimetic, self-adaptive porous flap system on bluff bodies that significantly reduces drag by modifying flow topology and dynamically interacting with vortex shedding across various flow conditions.

Contribution

The paper presents a novel passive, biomimetic control device with self-adaptive porous flaps that effectively reduces drag and alters flow behavior on bluff bodies.

Findings

Achieved up to 22% drag reduction.

Flow topology is significantly modified by the control system.

Flap dynamics are sensitive to Reynolds number and exhibit lock-in with vortex shedding.

Abstract

The performances of an original passive control system based on a biomimetic approach are assessed by investigating the flow over a bluff-body. This control device consists in a couple of flaps made from the combination of a rigid plastic skeleton coated with a porous fabric mimicking the shaft and the vane of the bird's feathers, respectively. The sides of a square cylinder have been fitted with this system so as to enable the flaps to freely rotate around their leading edge. This feature allows the movable flaps to self-adapt to the flow conditions. Comparing both the uncontrolled and the controlled flow, a significant drag reduction (up to 22%) has been obtained over a broad range of Reynolds number. The investigation of the mean flow reveals a noticeable modification of the flow topology at large scale in the vicinity of the controlled cylinder accounting for the increase of the pressure base in comparison with the natural flow. Meanwhile, the study of the relative motion of both flaps points out that their dynamics is sensitive to the Reynolds number. Furthermore, the comparative study of the flow dynamics at large scale suggest a lock-in coupling of the flap motion and the vortex shedding.