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fluids

My PhD: Vortex Generation and Modeling

My PhD focused on the “Experimental Generation and Modeling of Vortical Gusts and Their Interactions with an Airfoil.” You can see my thesis here.

I was interested in seeing the effect of a vortex interacting with a parallel wing. Most research on the topic has been based on helicopters or propellers, but those have periodically repeated interactions with the generated vortices. Other experiments used a pitching upstream airfoil to create a vortex, but this continuously released an intrusive wake that muddled the results. I figured out a simple way to generate a vortex that would then travel downstream and interact with a wing, and minimize that wake interaction: flapping a plate.

When a plate/airfoil changes its direction of motion or angle of attack, it also changes its bound circulation, and so by conservation of circulation, a corresponding amount is released.  After a lot of particle image velocimetry (PIV) experiments, I was able to show that the strength of the shed vortex is well modeled by the very basic models of thin airfoil theory. This was true for both the flapping plate, and the pitching airfoil.

I performed many PIV experiments to examine the vortex-wing interactions. Comparison with simple inviscid simulations showed good agreement until the vortex passed close to the wing. The viscous effects on the wing were too much in some cases, and the flow sometimes separated or behaved in complex ways. The old method with the pitching airfoil resulted in significant and permanent changes in the forces on the wing. The new method, with my flapping plate, did not. This new system was able to reveal a previously unavailable behavior: the resumption of vortex shedding from the perturbed wing.

For more detail about my thought process through the thesis, have a look at this post.

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