Here's the flame.
Prop makers have known that for a long time. That's why the TCDS for certified airplanes specify which props may be used, and those props are very often designed to satisfy the airframe manufacturer's engineers. They might want more or less pitch in the center area for more or less cooling flow. They might even want more blade area in the center. If you sight down some propellers, especially along the trailing edges, you can see some fairly abrupt changes.
The other problem with the prop: it's travelling upward on one side and down on the other, so the two sides see different airflows, even in level flight. Pretty hard to design a prop to handle both sides well. If the airflow is moving outward and downward around the cowl, for instance, the upgoing blade has a higher AoA than the downgoing blade. At the bottom, the airflow is moving sharply downward, while at the top it's almost straight.
Wind tunnels with smoke streams have been used for a long time to see this. Computers can probably do it much more easily and cheaply now. But the problem of uneven divergent flow is still there unless you're flying a round engine.