Inverted Flags

 A flapping inverted flag has been deflected to the right by incoming flow, which is coming out of the page.

A flapping inverted flag has been deflected to the right by incoming flow, which is coming out of the page.

We have all observed at one point or another in our lives that flags flap behind their pole when there is wind. This phenomenon is an example of the more general problem of flexible plates interacting with fluid flows.

In our group, we are interested in the opposite configuration: that of the "inverted flag." In this case, the leading edge of the plate is free to move while the trailing edge is clamped. This inverted flag configuration presents rich and complex dynamics and is ubiquitous in nature; some examples are the leaves rustling in a tree and flowing hair/fur follicles when animals run.

The inverted flag undergoes large-amplitude flapping under specific flow conditions. This makes it particularly useful for applications such as harvesting energy from the wind. Our focus is understanding the behavior of the inverted flag and how it changes with different parameters, such as wind speed, morphology or flag stiffness. We hope to use this knowledge to be able to design mechanisms that naturally present an inverted flag configuration in a safe and optimal way.