How can one make a fluid eddy?

To create a fluid eddy, you can introduce an obstruction or a change in flow direction in a moving fluid, such as water or air. This disturbance causes the fluid to swirl around the obstacle, forming a rotating motion. The velocity and viscosity of the fluid, along with the size and shape of the obstruction, will influence the strength and size of the resulting eddy. Techniques such as stirring or using barriers can also enhance the formation of eddies in a fluid.