Vortex Knots in Non-Ideal Fluids

In ideal fluid flows, vortex lines tied into knots may never untie, resulting in a conserved quantity known as helicity. Although the conservation of helicity in `perfect' fluids has a long history, far less is known about the behavior of knotted structures in non-ideal fluids, e.g. those with viscosity. I will discuss the first experiments to generate vortex knot in viscous fluids, as well as our more recent efforts to study knots in simulated superfluids.