Here's yet another fan duct for the  Ender 3. The goal of this was to design something simple, clean, and solid that works with the stock fans and hardware and can be printed without supports as long as your printer can handle a 16 mm bridge and 45 degree overhangs.
If you've upgraded or plan to upgrade to a larger 5015 part cooling fan check out my new upgraded design here:
https://www.thingiverse.com/thing:4528533
The V59 file adds a hole behind the fan to access the top mounting screw straight on rather then from the side with a ball end allen wrench as shown in my photos. I haven't bothered to actually print this version myself yet to verify how well it works, since the V52 currently on my machine works fine. So I left the old files here.