15.4* Flashcards
Why are mid-span shrouds used on fan blades?
They keep blade deflection within safe limits when the blades are subject to heavy loads
Why are mid span shrouds coated with a special coating?
To allow shrouds to slide against each other
What is the purpose of the Kevlar wrap and what other method is available for this task?
To provide blade containment in case of failure, the other method is an extra thick casing
Where would you find the moment weight for a fan blade?
On the root of the blade
Where are abradable shrouds found on a fan module?
On the inner wall of the fan case
What effect do stator vanes have on the air flowing through the compressor?
They guide the air onto the next stage and slow the air to increase pressure
What effect does the last set of stator vanes on the airflow to the combustion chamber have?
They straighten the airflow and cause it to slow down
What effect will increasing the airflow velocity have on the angle of attack of a blade?
The angle of attack reduces
What is a compressor stall?
Airflow separation from the compressor aerofoils causing turbulent flow across the stage, the engine rpm drops and the engine can run roughly
What is a compressor surge?
A strong stall that affects all compressor stages.
Generated by rapid decrease or airflow-causes stall
Leads to airflow blockage-creates stronger stalls
Causes low pressure areas where airflow can stop and reverse in movement
What methods can be employed to reduce or prevent stall or surge?
Variable stator vanes, variable bleed valves and multi spool compressors
What is the maximum amount of stages allowed on a centrifugal compressor engine?
Two
What is the make up of a compressor stage?
Rotor followed by stator
How are modern compressors built up?
They are built up of welded discs forming drums, multiple drums then make up the compressor
What limits the effectiveness of a multistage centrifugal compressor?
The loss of air pressure due to the changes of direction within the system
What is the purpose of an actuation ring?
To ensure that all VSV’s on one stage move at the same time
Why is the forward potion of the rear compressor case located inside the rear of the forward compressor?
It allows closer clearances between the blade tips and the compressor case as the forward case takes the load
What are the three different methods of securing rotor blades?
Axial dovetail slots, circumferential dovetail slots and bolts/pins
What is the purpose of the CDP seal?
Prevents compressor discharge air escaping into bearing area below the combustion chamber
What determines the compressor bleed positions?
The manufacturer selects the position depending on the pressure achieved at each stage
