Try and show a starting vortex from a foil in water or the hygroscopic fluid.
Dye the tip of the foil and then starting from rest pull the foil through the
water. You could note how the vortex changes strength with how fast you
move the foil through the water, though this will be hard to control without
a lot of apparatus. Does the vortex change size if you pull through the water
more quickly or just rotation rate?
Explore lift as a function of flow speed and angle of attack of an airfoil placed in the wind tunnel. Try and visualize the flow over the airfoil.