CFD (computation fluid dynamics) is essentially a virtual wind tunnel test. In the past, a really powerful computer was needed to crunch the simulation in a timely manner. These days, we can use cloud based software such as Simscale. Best of all, it's completely free for enthusiasts.

In this video, I take you through an example tutorial where a part cooling fan duct is optimised for a 3D printer. I'm not an aeronautical engineer, but what is here should be enough to get you going. There is a lot of documentation, but much of it is out date, incomplete or hard to find. Hopefully this video can help overcome this.

Simscale: https://www.simscale.com
Airflow calculator: https://www.engineering.com/calculators/airflow.htm

Models and simulations shown in this video:
Little jet plane: https://www.thingiverse.com/thing:222309
Petsfang part cooling fan duct: https://www.thingiverse.com/thing:2759439
Thermal analysis by Aravindbaskar: https://www.simscale.com/workbench/?pid=1936080569646282774
Super layer cooler CFD…