Influence of Mechanical System Design on the Response of an Airfoil to Predicted, Coherent Fluid Forcing

How should we design an engineering system to leverage a predicted incoming flow field for improved drag reduction?

Fish swimming in a stream exploit coherent structures generated in their environment to save energy by reducing drag over their bodies. It has even been shown that without active control by the animal, a fish’s body can ‘lock in’ to vortices shed by a cylinder, generate enough thrust to overcome drag entirely, and begin to swim upstream [1]. This passive thrust production, harnessed in an engineering context, offers a potential low-control effort method of reducing drag in environments where coherent structures exist and are predictable. Development of a low-order model to describe the important physical parameters of a prototypical engineering system will facilitate control design to exploit this behaviour, and demonstrate the utility of this phenomenon in an engineering context.

Figure: Airfoil mounted and ready to move. The all-mechanical mounting system allows the hanging airfoil to pitch and heave freely in the NOAH Water Tunnel facility, while measuring the forces and torques applied as well as the linear and angular position of the airfoil. Photo by Morgan Jones.

Morgan Hooper, Beverley McKeon

Funding from an NSERC PGS-D and ARO gratefully acknowledged.

References

1. D. N. Beal et al. “Passive Propulsion in Vortex Wakes". In: Journal of Fluid Mechanics 549 (2006), pp. 385-402.