A quick centrifugal fan design I made. I attempted to make a bell inlet however I did it wrong and it didn't change anything. Decent airflow rate.

Impeller attaches to a generic brushed hobby motor that is mounted to the back of the housing, with the rotor shaft sticking out through the hole in the back of the housing.

Impeller mounting hole may need to be drilled out due to lack of tolerance. Use a 1mm drill bit, or a drill bit appropriate to the size of the shaft of the motor you're using.