M15.3 Flashcards
(56 cards)
What does the air intake have to allow for smooth airflow?
A intake nose
What is the shape called when the air inlet duct gets wider?
A divergent duct
What does the divergent duct use to increase static pressure?
Bernoulli principle
What happens with supersonic airflow?
It’s compressible so engine parameters are reversed
What speed should the airflow be at the compressor inlet?
Between Mach 0.4 and 0.7
How do air intakes convert decelerate airflow?
By converting kinetic energy to pressure energy
What happens to velocity and pressure in subsonic inlet ducts?
Velocity decreases
Pressure increases
What is the most efficient inlet configuration for subsonic flight?
The pitot type quasi - circular diffuser
When do you get problems with subsonic inlet ducts?
When a/c on ground with max thrust because of core depression
What does making the inlet lip rounded result in?
A thicker radius
What does having a thicker radius inlet do?
Reduces the risk of flow separation
Why are large inlet lips avoided?
Because it hinders performance at high speeds
What is fitted to an intake to minimise the issues with crosswind?
With cross wind components which are fitted to the intake
What speeds is the pitot type intake good up to?
Mach 1.5
What does the pitot tube do at transonic speeds?
And how is this done?
Keeps shock wave out
By using a normal shock diffuser
What does a normal shock wave do?
Increase temp pressure and decrease velocity
What happens when rpm is reduce?
The pressure in the inlet rise allows less air in.
What must the cross sectional area of a transonic duct allow?
And what is this called?
Max airflow requirements that apply to only 1 Mach number and altitude
Critical condition
What is super critical condition?
When pressure in the diffuser is decreased causing normal shock to be drawn further to the inlet
What is sub critical?
When the normal shock wave is expelled due to an increase of pressure in the diffuser
What is diffuser buzz?
Caused when there is extreme pressure fluctuations
What happens to the shock wave in super critical, sub critical and critical?
Super critical = moves closer to intake
Sub critical = moves further from intake
Critical = perfect position
When does a normal shock wave occur?
When a/c at low supersonic speeds and stands perpendicular to airflow.
What happens to velocity and pressure in a normal shock wave?
Velocity drops from supersonic to sub sonic
Pressure rises
