Which direction do the gas generator turbine and the power turbine module spin?

• A. Gas Generator Turbine: Clockwise; Power Turbine: Counter Clockwise
• B. Gas Generator Turbine: Clockwise; Power Turbine: Clockwise
• C. Gas Generator Turbine: Counter Clockwise; Power Turbine: Clockwise
• D. Gas Generator Turbine: Counter Clockwise; Power Turbine: Counter Clockwise

Answer: (C)

In a two-shaft gas turbine setup, the gas generator drives the compressor on one shaft while the power turbine drives the output load on a separate shaft. The mechanical path from the power turbine to the generator (usually through a gearbox or coupling) is arranged so that the two shafts rotate in opposite senses. This opposite rotation helps fit the gear train geometry and ensures the external load, like the generator, receives rotation in the desired direction while keeping the internal turbine components properly balanced and aligned. So the gas generator turbine turns in one direction (for example, counter clockwise) while the power turbine turns in the opposite direction (clockwise).