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Originally Posted by freebeard
I posted that to show how much my thinking has changed since hanging around here (but didn't say so, sorry). Water might make a rooster tail but air not so much.
How much divergence is too much? A trumpet bell runs out to 90° axially. I thought they couple to the ambient air most efficiently.
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For pipes and ducts the optimum angle for a conical diverging section depends on the k-factor (smoothness) of the boundary walls.But the drag minimums are at the 6-8 degrees range.
For a diffuser,there is a overall drag reduction with angles up to 11-degrees,but the minimums are at 2.8-degrees,to 4-degrees,depending on where the up-sweep begins.
Laterally,against the sidewall of the wheel fairing,I suspect that you'd mirror that angle,otherwise you'd have an asymmetrical pressure rise leading to vortice formation.
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On the drive here this morning,the Denton High Marching Band was crossing the street in front of me.I was watching the horn bells.I'm not an acoustics guy,but my thoughts went to a reversed-ear.
Our ears concentrate sound into the ear passage.
The bell on the horns may reverse this to 'broadcast' the sound pressure waves.Purely an acoustic,sonic wave function,rather than aerodynamic function.