1
Q
What are the 4 purposes of an intake?
A
- Guide air
- Set the right velocity & pressure of inlet air
- Minimize pressure loss, low distortion
- Static pressure rise by flow deceleration
2
Q
What are 3 challenges of intakes?
A
- Separation (high-pressure gradient)
- Non-uniform or distorted flow may cause compressor surge
- Create drag as low as possible
3
Q
What are the 2 intake types?
A
- Subsonic flight
- Supersonic flight
4
Q
What are 4 properties of subsonic intakes?
A
- Rounded edges, relatively short arrangement
- Low static pressure rise
- Low total pressure loss
- Causes distortion to fan and compressor at high incidence or cross-wind (moderate aerodynamic interaction of intake and compression components)
5
Q
What are 5 properties of supersonic intakes?
A
- Sharp edges, long and potentially variable arrangement
- High static pressure rise
- High total pressure loss
- Causes distortion to fan and compressor at any flight
condition (strong aerodynamic interaction between
intake and compression components) - Can develop intake buzz
6
Q
What are the 2 purposes of a fan?
A
- Efficient thrust generation
- High Bypass Ratio
7
Q
What are the 6 purposes and properties of a propeller?
A
- Convert Shaft torque to thrust
- Turbine provides shaft power to the gas generator
- Very large BPR between 30-100
- Higher propulsive efficiency
- Cruise Ma 0.4-0.6 and 0.7-0.8 for advanced configurations
- Reduction gearbox required (increase engine weight)
8
Q
What is the primary and secondary purpose of a compressor?
A
- Primary: Increase pressure of air mass, delivery at
correct velocity, temperature, and pressure - Secondary: Supply engine with bleed air
9
Q
How does a compressor work?
A
- Acceleration of working fluid
followed by diffusion - Transforms kinetic energy to pressure
10
Q
What are the 3 design targets for a compressor?
A
- Increase stage pressure ratio (PR)
- Increase efficiency
- Maintain trouble free function (surge)
11
Q
What are the 2 types of compressors?
A
- Radial compressor
- Axial compressor
12
Q
What are the advantages and disadvantages of radial compressors?
A
+ Robust
+ Easier to develop / manufacture
+ High PR per stage
+ Good efficiency for a wide RPM range
+ Low weight
- Large frontal area for given mass flow
- More than two stages are not practical
13
Q
What are the advantages and disadvantages of axial compressors?
A
+ More Air for same frontal area → Higher
thrust
+ More stages → higher PR and lower drag
+ High peak efficiencies
- High cost
- High weight
- Lower PR per stage
14
Q
What are the 2 purposes of multi-spool design?
A
- Increases design operation flexibility
- Varying LPC output provides the HPC with the best inlet conditions within the limits of its design
15
Q
What are the 4 purposes of a combustion chamber?
A
- Prepare and burn air-fuel mixture to facilitate the addition of heat
- Increase total temperature via intensive heat input to flow
- Serve the engine cycle: Add heat in the core between
compression and expansion - Large working range: 0,3 to 45 bar, -30 to 1750 °C
16
Q
What are the main parts of a combustion chamber?
A
- Outer casing
- Inlet diffuser (HPC interface)
- Inner casing (protect HP shaft)
- Fuel nozzles
- Igniters
17
Q
What are 4 important design details of a CC?
A
- Low Mach Number entry flow
- Fuel injection
- Fuel/air mixing
- Multi-zone combustion to achieve low
emissions
18
Q
How is efficient combustion achieved?
A
- Proper mixing
- Stable burning
- Cooling of hot combustion products down to an adequate level for HP turbine parts (TET limit, HPT interface)
19
Q
What are 10 design criteria for a CC?
A
- Stable combustion process over a wide range of pressures
and temperatures under all conditions (e.g., humidity, rain,
hail, birds …) - Adequate re-light capability on the ground and at altitude
- Low noise and avoidance of acoustic phenomena such as
„Buzz“ and „Rumble“ - Complete combustion (>99 %)
- Low total pressure loss
- Rapid quenching (rapid air addition), low pollutant emissions (NOx, Soot,
CO, UHC) - Reasonable wall temperature, long parts life (controlled crack formation and
propagation) - Optimum temperature distribution at the exit to permit turbine life
- Minimum volume, length, and weight (aero engines)
- Low design and maintenance cost
20
Q
What are 4 design goals of a CC?
A
- Maximize heat release
- Minimize size
requirements - Reduce fuel emission
- Emissions
21
Q
What are 3 purposes of a turbine?
A
- Satisfy thermodynamic cycle requirements across flight envelope (altitude and Manumber)
- Facilitate the transformation of fluidic energy to mechanical/rotational energy
- Provide work to compressor/shaft
22
Q
What are 7 characteristics of a turbine?
A
- Located at the back of the engine
- Significant LPT Reynolds number effects
- Working with extreme temperatures and pressures
- High aerodynamic loading at the highest efficiencies
- Complex cooling systems
- Complex part-life requirements
- Continued strong demand for new high-temperature materials
23
Q
What is the turbine assembly of a 2-Shaft arrangement?
A
- Low BPR engine hence little mean radius change
through the turbine - 2-stage HPT (shrouded, cooled)
- 3-stage LPT
(shrouded, no blade cooling) - HPT stage 2 is similar to IPT in a modern 3-shaft
engine - LPT stator vane 1 is a special design:
- in a transition duct, including structural struts
- to lead through oil supply
- to allow borescope access
- to accommodate temperature measurement
24
Q
What are 9 general design requirements of a turbine?
A
- Design structure to form the inner and outer main gas path
- Lead occurring forces into the rotor and the casing
- Have sealing against hot gas entry and cooling flow leakage
- Quantify turbine flow capacity: fix annulus and throat areas
- Structural integrity of components
- Meet Creep, Oxidation, and Fatigue requirements
- Minimize weight
- Allow cost-oriented manufacturing
- Allow cost-oriented repair and overhaul schemes
25
What are the 6 properties that describe a nozzle?
- The sensitivity of engine net thrust to nozzle performance is
higher than to any other engine components performance
- Therefore, maximize nozzle performance with consideration
of cost, weight, complexity, reliability, and maintainability
- The type of nozzle is largely determined by the combination
of engine aircraft and mission requirements
- Fixed conical nozzles are the simplest variant (no moving
parts, purely converging exhaust duct)
- They are used for subsonic transport aircraft in common or
separate nozzle arrangement
- Variable nozzles are applied on engines, which require a
large variety of nozzle exit areas, mainly as a consequence
of afterburning (area increase of 50-150% )
26
What are the 3 types of nozzles?
- Nozzle + Mixing
- Separate Jets / Nozzles
- Variable Vector Nozzle
27
What are 4 properties of Nozzle + Mixing?
- Used for low/medium BPR
engines to reduce hot jet noise
- Improved overall nozzle
efficiency
- Long nacelle + bypass duct
- Moderate impact of the nozzle
on fan and core throttling
28
What are 4 properties of Separate Jets / Nozzles?
- Used for high BPR engines as
the hot jet stream is low
- Bypass nozzle efficiency
improved using chevron edge
- Short nacelle + bypass duct
- Moderate impact of the nozzle
on fan and core throttling
29
What are 4 properties of Variable Vector Nozzles?
- Used for afterburner
supersonic flight engines
- Variable mechanism to control
throat area and thrust vector
- External arrangement
- Strong impact of the nozzle on
fan and core throttling
