Does flutter prevent drag reduction by reconfiguration?

Area of Science:

• Fluid dynamics
• Structural mechanics
• Aeroelasticity

Background:

• Static reconfiguration of flexible beams in transverse flows reduces drag.
• Flexible beams in axial flows can experience flutter instability, increasing drag.
• The net effect of flexibility and flapping on drag in reconfiguring structures is unclear.

Purpose of the Study:

• To investigate the impact of flapping motion on the drag of reconfiguring flexible beams in axial flows.
• To determine if flexibility enhances or alleviates drag when flapping occurs.
• To quantify the drag reduction benefits of reconfiguration versus drag increase from flapping.

Main Methods:

• Numerical simulations using reduced-order models.
• Analysis of drag forces on flexible beams undergoing static reconfiguration and dynamic flapping.
• Comparison of drag on flexible structures with a rigid structure reference.

Main Results:

• The additional drag from flapping motion is generally not significant enough to negate drag reduction from reconfiguration.
• Isolated, brief snapping events can transiently increase drag above that of a rigid structure for heavy, moderately slender beams.
• Drag force remains significantly reduced compared to a rigid structure, except for these short peak events.

Conclusions:

• Flexibility in reconfiguring beams primarily leads to drag reduction, even with flapping.
• The drag-increasing effect of flutter instability is typically outweighed by the drag-reducing effect of reconfiguration.
• Reconfiguring flexible structures offer a net drag reduction benefit in axial flows.