It tries to resemble a traditional recorder flute by having 7 "holes" over it and one under it. The holes are actually covered by thin copper pieces which work as capacitive sensors. I recommend using cut copper nails of good size, even though the photos at the moment have only bare wires in a spiral shape. The mouth piece has no acoustic properties and simply directs the air flow to a air flow sensor component MPXV7002DP. The outward facing tip has tray where Arduino Nano can be slided in after the wires have been soldered. The cap keeps it in place and USB cable can be connected through it. There is also extra room to take out a thin cable if you want the serial TX to also work with real MIDI port.
The firmware is on Github which acts as a serial midi device and sends notes for a synthesizer when a proper finger combination is detected along some noticeable air flow. The "power" of the air flow adjusts the velocity.
Assembling and printing tips:
There is an extra hole for passing through the air flow sensor wires and it would be a good idea to apply some hot glue to it after passing the wires so that it is air tight.
The upward positioned model is good for printing but cabling can be tricky. For that purpose I made horizontally modelled model of two halves which makes that a lot easier, but I have not yet tried to print it and it needs glueing after cabling. I recommend using the upwards positioned model.