Summary of Compressor and Turbine Characteristics

Axial and Radial Compressor Construction
Large gas turbines utilize axial compressors made up of rotating rotors and stationary stators. The rotor blades carry rows attached to a shaft, while stators, fixed within the casing, feature stator vanes. Each rotating rotor and fixed stator combination creates a stage, causing a rise in gas velocity as energy is added. This leads to conversions from velocity to pressure and temperature gains throughout the compression process, with total pressure and temperature increasing through the rotor but remaining constant in the stator due to its lack of energy input.

Pressure and Density Dynamics
A cross-section of a compressor shows increased pressure and density as outlined by the conservation of mass. To manage higher density gas flow, compressor blades need to be shortened, which can be achieved by reducing casing diameter or increasing shaft diameter. A smaller casing maintains airflow, while a larger shaft ensures even rotor diameter, reducing airflow disruptions and aligning better with turbine designs.

Rotor Design Choices
Designing a rotor involves choosing between a drum or disc style, impacting weight and speed capabilities. Blade attachment methods include fir tree and dovetail, with the former offering a stronger connection. Additionally, axial mounting provides better protection against foreign object damage compared to circumferential mounting.

Blisk and Bling Designs
To minimize engine weight, blades may be combined with discs into a blisk or a ring-shaped bling design. However, a failure in one blade of a blisk necessitates replacing the entire unit. The compressor aims for maximum pressure increase per stage, resulting in optimized blade designs dependent on airflow characteristics.

Airflow Dynamics
Understanding airflow around blades is complex due to the interaction between absolute velocity (observed externally) and relative velocity (as perceived on a rotor blade).

Centrifugal vs. Axial Compressors
While axial compressors feature air whirling around, centrifugal compressors fling air outward. The impeller mimics the axial rotor while a diffuser acts like the axial stator, leading to distinct advantages like higher rotational speeds and shorter designs. However, centrifugal compressors have lower isentropic efficiency and can be cumbersome on larger scales.

Applications of Centrifugal Compressors
These compressors are effective in small engines, especially in auxiliary power units for non-propulsion purposes, due to their space-efficient design and pressure ratios.

Velocity Triangles and Turbine Comparison
In radial compressors, airflow enters axially with distinct velocity triangle components, but turbines differ significantly as they operate on high pressure and temperature airflow. Turbines convert pressure into work, leading to higher handling capability compared to compressors. Effective cooling in turbines is crucial, as high temperatures pose risks of leakage and inefficiency, requiring strict design considerations for blade and casing relationships.

Energy Conversion Dynamics
The operational dynamic contrasts between compressors and turbines: in compressors, rotors convert work into velocity and then pressure, whereas in turbines, the stator and rotor first convert pressure into velocity, followed by work extraction. This fundamental difference is essential in understanding gas turbine applications where compressor passages are widened and turbine passages narrowed to manage pressure and velocity appropriately for optimal performance in various operational contexts, whether in industrial setups or aero engines.