Final answer:
The propellers of a free-spool turboprop are driven by the flow of air or gas. The power turbine, which is not directly connected to the rest of the engine, rotates freely and is driven by the flow of exhaust gases. This rotation drives the propellers and generates thrust.
Step-by-step explanation:
The flow of gas or air powers the propellers of a free-spool (free turbine) turboprop. The power turbine in a free-spool turboprop is free to rotate since it is not directly connected to the rest of the engine. Exhaust gas flow powers the power turbine, whose rotation powers the propellers.
For instance, the turbine and propeller system are linked in an airplane. The propeller blades are turned by the rotating turbine shaft, which creates thrust that propels the aircraft forward.