To 3d print this model, I suggest 3 or 4 perimeters, no support, infill at your discretion and at least 300 microns of precisions.
Here is another version of my previous 4 inches duct. This one is for a 5 inches blower fan. Personnally, I do not own one this size, but I decided to publish this version for those of you who needs a 5 inches fitting. It is a fan duct dedicated to various application, but it's main purpose is to replace and/or extend a traditionnal 120mmx120mmx38mm fan to a 5 inches piping, such as a 5 inches blower fan, etc. It is designed to fit with the same screws used with the original fan, you won't need to replace them for a shorter or longer version. Can be used to replace the stock fan ( exit end) of a Antminer (s9 by exemple) with this duct and fix at the end of it a 5 inches industrial blower to lower noise and also greatly increase cooling. I hope this will help you, if you wish to 3d print it, share it or modify it for your personnal use, feel free to do so. If you like it, give it a like, this will be my reward! I apologise for the bad english by the way!
Happy 3D printing AND mining!