There are a few ways to try to achieve this. One good way is to use the “Waterfall” effect, which is the last effect in “Sandbox Effects” at the end of the Effects tab:
– Choose Waterfall
– Change the rotation to 90
– Click about a 1/4 way through the wheel (you can experiment with different positions)
– Increase fade to about 20
– Click the paintbrush icon, click the “Reverse Effect” checkbox on the panel that opens, and paint over just the wheel
– Unclick the paintbrush icon and experiment with clicking on different parts of the wheel