• Large frontal area required for a given airflow increases aerodynamic drag. • The practical limitations on the number of stages restrict scaling up for larger and more powerful engines. (compressor section limited to two stages) Disadvantages of Centrifugal Flow Compressors
Unlike a centrifugal compressor, which is capable of compressor pressure ratios of 15:1, a single stage in an axial flow compressor is capable of producing a compressor pressure ratio of only 1.25:1. The only way to achieve high compressor pressure ratios with an axial flow compressor is by adding more compressor stages. Axial Flow Compressor
The TWO MAIN ELEMENTS of an AXIAL FLOW COMPRESSOR: Rotors Blades & Stators Vanes Rotor section increase in pressure Stator section decrease in pressure
The number or stages is determined by the amount of air and total pressure rise required in the design of the engine. Airflow velocity remains nearly constant as air pressure increases while air flows through each stage of compression. The overall result is increased air pressure with relatively constant air velocity from compressor inlet to outlet.
AXIAL FLOW COMPRESSOR The convergence maintains a constant air velocity as air density decreases in each stage of compression.
DISADVANTAGES OF AXIAL FLOW COMPRESSORS: • Relatively high weight • High starting power requirements • Low-pressure raise per stage of 1.25:1 requires many stages to achieve high compressor pressure ratios. • Expensive • Difficult to make
ADVANTAGES OF AXIAL FLOW COMPRESSORS: • Outperform centrifugal flow compressors in several areas. • Straight-through design improves ram efficiency. • By adding stages, higher compressor pressure ratios are possible. • Small frontal area reduces aerodynamic drag.
The airfoil cross-section used in an axial flow compressor has a varied angle of incidence, or twist. The twist compensates for variations in blade velocity caused by relative distance from the rotational axis, the faster it travels. Axial flow compressors typically have 10- 18 compression stages. In turbofan engines, the fan is considered the first stage rotor. Compressor Rotor Blades
COMPRESSOR STATOR VANES Stator vanes are stationary blades located between each row of rotor blades in an axial flow compressor. Stator vanes diffuse air coming off the rotor, which decreases its velocity and increases its pressure. Stators also help prevent swirling by directing the flow of air from one stage and delivering it to the next at an appropriate angle. Like rotor blades, stator vanes have an airfoil shape. The AOA for stator vanes can be fixed or variable.
INLET GUIDE VANES Stator vanes positioned in front of the first stage rotor blades are called inlet guide vanes . These vanes direct airflow to the first stage rotor blades at the best angle while creating a swirling motion in the direction of engine rotation.
Variable Inlet Guide Vanes and Stators Some axial compressors with
You've reached the end of your free preview.
Want to read all 113 pages?
- Spring '14
- Turbofan, Gas turbine, Gas compressor, Axial flow compressor