Unsteady Aerodynamic Flow Visualizations

Research Abstract:
Taking inspiration from bird and insect flight, researchers have been able to design micro air vehicles, ornithopers, and oscillating wing energy harvesters. To visualize the fluid flow around these structures a soap film tunnel is used.

Fluids are experimentally hard to study because of difficulty to observe fluids motions. The soap film tunnel is a quite simple and cost efficient way to visualize two-dimensional flows. This apparatus works by mixing a soap solution that falls by gravity from a top reservoir to a bottom reservoir between two wires. The wires are pulled apart, which creates the soap film. Various objects can be placed within the film that will create a wake that can be photographed. This is possible by light hitting the film and causing interference. With the correct lighting the interference can be captured with the use of a high-speed camera. The soap film tunnel will be used to analyze the wake behind different objects. Each object creates vortices in the wake that allow us to study the flow.

The current research investigated the effect of waveform on the development, timing, and shedding of leading edge vortices. The videos below show different flow regimes for simple sinusoidal heaving and pitching (a) and sinusoidal heaving with almost square wave pitching (b).

(b)