Compressors Flashcards
What is the primary purpose of a compressor?
to increase pressure by guiding the flow of air through a series of carefully shaped channels
How are the channels in a compressor obtained?
as a consequence of the arrangement of the stationary stator and rotary rotor
Does the compressor do work on the fluid?
no, so it requires a power supply
Where is the work exchanged between?
the fluid and machine only in the rotor
What is one pair rotor/stator called?
a stage
What is happening to the pressure inside the compressor channels?
pressure is increasing to avoid flow separation
What does absolute velocity do?
increases across the rotor and diminishes across the stator, pressure increases
What does relative velocity do?
decreases across the rotor, pressure increases
What are axial compressors?
machines where air enters and leaves in a direction parallel to the axis of rotation
What can be said about the pressure increase in the compressor?
it is gradual
What is the pressure rise typically between?
1.1 and 1.6
What is necessary to maintain constant axial velocity?
a gradual decrease in the area between the rotor shaft and the stator casing
What does the last row of stators do in a compressor?
they ensure that any residual swirl within the flow is removed before the flow passes into the combustion chamber
What do centrifugal compressors do?
they realise a pressure increase by means of a combination of channel shape and centrifugal effect which establishes a radial flow
What are some benefits of the centrifugal compressor?
more robust than the axial type
easier to develop and manufacture
What happens in a centrifugal compressor?
> the impeller rotates at high speeds and is continually induced into the centre of the impeller
centrifugal action causes it to flow radially outwards along the vanes on the surface of the impeller disc
this accelerates the air causing a slight increase in pressure
air leaving the impeller passes into the diffuser section where the vanes from divergent passages
What can be said about each single stage of the centrifugal compressor?
each stage has a higher compression ratio than a single axial stage
r between 4-6
What should the combustion chamber be capable of?
*complete combustion of large quantities of fuel
*small volume and minimum pressure loss
*deliver uniform temperature
*exit temperature low enough for turbine blades
*expected life of the order is 10,000 hours
*produce low nitrous oxide and hydrocarbon emissions
*operate over the whole range if engine speed, flight speed and altitude
What does the typical configuration of a combustion chamber include?
*injection zone
*ignition zone
*primary combustion zone
*seconday combustion zone
*tertiary combustion zone
