Leveraging three-dimensionality for navigation in bluff-body wakes

TL;DR

This paper demonstrates that autonomous swimmers can efficiently navigate complex unsteady wakes by exploiting three-dimensional flow structures, even with limited sensing, using model-predictive control.

Contribution

It shows that three-dimensional flow features can be leveraged for energy-efficient navigation in unsteady wakes with limited flow information, advancing autonomous vehicle control.

Findings

3D flow structures improve navigation speed.

Navigation feasible with limited flowfield data.

Leveraging secondary vortices enhances efficiency.

Abstract

Biological flyers and swimmers navigate in unsteady wake flows using limited sensory abilities and actuation energies. Understanding how vortical structures can be leveraged for energy-efficient navigation in unsteady flows is beneficial in developing autonomous navigation for small-scale aerial and marine vehicles. Such vehicles are typically operated with constrained onboard actuation and sensing capabilities, making energy-efficient trajectory planning critically important. This study finds that trajectory planners can leverage three-dimensionality appearing in a complex unsteady wake for efficient navigation using limited flowfield information. This is revealed with comprehensive investigations by finite-horizon model-predictive control for trajectory planning of a swimmer behind a cylinder wake at Re=300. The navigation performance of three-dimensional (3D) cases is compared to scenarios in a two-dimensional (2D) wake. The underactuated swimmer is able to reach the target by leveraging the background flow when the prediction horizon exceeds one-tenth of the wake-shedding period, demonstrating that navigation is feasible with limited information about the flowfield. Further, we identify that the swimmer can leverage the secondary transverse vortical structures to reach the target faster than is achievable navigating in a 2D wake.