What function do axial flow turbine nozzles serve?

Axial flow turbine nozzles play a crucial role in directing the mass airflow towards the turbine rotor. Their primary function is to optimize the airflow entering the rotor by converting the thermal and pressure energy of the gas into kinetic energy. This is achieved by shaping the gas flow into a high-velocity stream that effectively strikes the blades of the turbine rotor, inducing rotation and thereby generating mechanical energy.

The design of the nozzles ensures that the gas is directed at the proper angle and at the correct velocity to achieve maximum efficiency in turning the rotor. This efficient airflow is essential for the performance of the turbine in applications such as jet engines, where propulsion relies heavily on the effective conversion of energy in the gases produced from combustion.

The other options, while relevant to turbine operations, do not accurately describe the primary function of axial flow turbine nozzles. For example, preventing backpressure and reducing noise are important operational considerations but are not the main purpose of the nozzle design. Similarly, while nozzles can contribute to overall fuel efficiency by improving the performance of the turbine, their primary function is explicitly focused on directing the mass airflow.