The problem is you have very messy flow originating from the fan with a ton of swirl, so it is likely not like the top left diagram and more like the bottom two

The problem is you have very messy flow originating from the fan with a ton of swirl, so it is likely not like the top left diagram and more like the bottom two. It's totally unsteady flow, like in this CFD: https://www.automotivetestingtechnologyinternational.com/wp-content/uploads/2021/05/Lead-e1620818346517.jpg https://www.automotivetestingtechnologyinternational.com/wp-... Wind tunnels use honeycomb flow straighteners to take care of this. A full blown analysis might use computational aeroacoustics software that can calculate the noise generated from solid geometry in a given flow. This field has advanced considerably since when the article was published due to newer methods like LBM. It'd be beyond the scope of journalism like this, but it is no doubt done by companies with resources like Apple.