Compressor and Turbine Overview

In this knowledge clip, we explore the constructions of axial and radial compressors and compare the properties of compressors and turbines. Axial Compressors consist of rotating rotors and stationary stators where rotors attached to a shaft carry blades that rotate, while the fixed blades, or stator vanes, aid in converting gas velocity into pressure and temperature gains. As the gas flows through a rotor and stator, total pressure and temperature increase due to energy added by the rotor, while the stator maintains constant conditions.

Key Equations: The combined gas law and Poisson equations indicate pressure and density increase as gas flows through the compressor due to reduced cross-sectional area while keeping velocity constant. The design must accommodate these changes, either by shortening blades, reducing casing diameter, or increasing shaft diameter.

When designing rotors, one must consider drum vs. disc designs; drum rotors are lighter but fragile, and discs handle higher speeds better. Blades can be attached with fir tree or dovetail attachments, with fir tree offering a stronger connection, although being pricier. Blade mounting can be axial or circumferential, with axial preferred at the front for damage resistance.

Centrifugal Compressors: These operate differently from axial compressors, expelling air outward while providing advantages like higher operational speeds, better pressure ratios per stage, and suitability for small engines. However, they also have drawbacks such as lower isentropic efficiency.

Compressors aim for maximum pressure increase, necessitating optimized blade designs. Understanding the airflow, including absolute and relative velocities, is crucial. In axial compressors, air moves with a mix of axial and tangential velocities, whereas radial compressors differ, having air enter axially with a velocity triangle indicating various flow dynamics.

Turbines vs. Compressors: Turbines convert high-pressure, high-temperature gas into work, facilitating engine components' operations. Turbines encounter fewer airflow issues due to their operational principle, allowing them to handle higher pressure ratios more effectively than compressors. Notably, turbine passages are narrower than compressor passages, and the design incorporates cooling measures due to high-temperature conditions. The conversions of energy in turbines and compressors are fundamentally opposite; compressors transform work into pressure, while turbines convert pressure into work.

In summary, distinguishing between compressors and turbines is essential for understanding their propulsion roles in gas turbine engines, with specific designs and properties tailored to their functional differences.