Does anyone know of any methods for designing a bellmouth? Are there certain design constraints? ie. the radius is equal to half the radius of the inlet tube. Thanks for the help.
I remember reading once that, ideally, the "bell" should do more than just curve away from the mouth of the intake, as seen in the photo you referenced. I read that the optimal shape is for the edge of the "bell" to curl back on itself rather than simply stop in mid air. I'll try a (greatly simplified) drawing...
The design of the bellmouth affects its design parameters. One for a jet engine intake is designed differently than one for a ducted fan. There is an inlet section, but ducts with bellmouth entrances also can either have a straight discharge, or can taper inward or outwardly.