I recently have been looking at different types of jet engines and came to this thread wherein they talk about how most of the thrust from airline turbofan engines (high bypass) comes from the bypass air and not the combusted air coming out of the internals of the engine.
So my question is, has there ever been a sort of fan engine used that only uses bypass air and the fan is run by a separate engine? Would this even be viable?
Edit:
Basically a turbofan that just uses the power of the increasing speed of the air through the smaller space, no combustion (other than the standard piston engine/electric motor/whatever).