We also need to consider the air that is in front of the train as it moves forward. That air is going into the portal at the rate the train moves forward and therefore coming out the other portal at that rate.

I have android 9.

Here is a relevant video to this subject. https://www.youtube.com/watch?v=IP2EKTCngiM

Id didin’t open source the game. They open sourced the game engine. So you can download gzdoom which is an open source port of the original doom engine, but you still need to own the original game for the game files in order to play it.