In turboprop and turbo shaft engines, what does 'free turbine' signify?

The term 'free turbine' in the context of turboprop and turbo shaft engines indicates that the turbine wheel is not physically connected to the turbine wheel. In a free turbine system, there are two sections: one is connected to the power-producing turbine that drives the compressor, and the other is the free turbine that converts energy to drive the propeller or rotor.

This design allows the free turbine to operate independently of the engine's power section, providing flexibility in power delivery to the propeller or rotor while optimizing engine performance and efficiency. The separation between the turbine sections enables the engine to produce power at varying speeds for different operational demands. Thus, the concept of a 'free turbine' fundamentally highlights the independence of this turbine within the overall engine architecture, distinguishing it from mechanically coupled turbine systems where all components would operate in sync.