What is the purpose of the inlet in an aero-engine?
- Reduce air velocity by a diffuser shaped duct, to a suitable velocity for the compressor
- Capture the exact amount of needed air with minimal distortion of the flow
How do subsonic inlets work and what is the most common type? What is its main requirement?
Pitot-inlet with fixed geometry.
Operate best at design point velocity.
The main requirement:
- Minimize pressure loss
- Ensure that the air enters the compressor with uniform pressure and velocity
How do subsonic inlets ensure stable airflow at slow velocities?
By having thick inlet lips that the flow will stay attached to even at low velocities
What are consequences of the flow being disturbed in subsonic inlets?
Compressor instabilities that may cause flameout or mechanical damage due to blade vibration
How do the inlets in turboprops work?
- Thick inlet lips
- “Reversed” flow
- Air scooped in underneath or beside propeller
- At aft limit, turned 180 degrees and moves back toward front
- Air is reversed again in combustor
What are advantages to the turboprop inlet?
- Allows shorter, compacter engines
- Robust against FOD
- Good for TO and landing on unpaved runways
What are different types of supersonic inlets?
- Pitot types
- Bifurcated systems
- Variable-geometry
- Intake spikes
Engine is normally buried inside fuselage
What are requirements for a supersonic inlet? Why are thick inlet lips unfitting for these airspeeds?
- Ensure stable airflow at a suitable velocity for the compressor
- Low radar cross section
- Flow stability during rapid manoeuvering
- Thick inlet lips are unfitting because of normal shock waves yielding a very sharp static pressure rise without changing flow direction and correspondingly large velocity reduction
How is intake of turbulent BL from the fuselage prevented in supersonic inlets?
- A gap between the inlet and the fuselage
- Bumper in front of inlet to redirect BL and slow down local airspeed
- Inlet positioned below the front section, so when rapid manoeuvering is performed the fuselage helps direct flow into inlet
How does the conditions for a stationary gas turbine engine vary from the aero-engine? What are challenges and importances?
- Relatively constant aerodynamic operation conditions
- Challenges: hot and dusty environments
- Necessary to protect these turbines with filters/coolers
What is a common technique for cooling stationary gas turbine inlets?
Spraying finely atomized water into the inlet
Name the three most common pitot-type intakes
- Podded intakes, common for transport aircraft
- Integrated intakes, common for military aircraft
- Flush intakes, common in missiles
