Flight Prop 2

• Supply engine with sufficient massflow

• Convert velocity to static pressure at convenient Mach number at the fan face

• Allow low inner and outer total pressure losses

• Supply uniform inlet flow profile to the fan

• Provide noise reduction

• Prevent ice accretion

• Achieve low weight at high structural stiffness

• Integration with fuselage/wing

• Low initial and operating cost

Subsonic Flight Intake

• rounded edges, relatively short arrangement

• Low static pressure rise

• Low total pressure loss

• Causes distorsion to fan and compressor at high incidence or cross-wind

Supersonic Flight Intake

• sharp edges, long arrangement, potentially variable

• High static pressure rise

• High total pressure loss

• causes distorsion to fan and compressor at any flight condition

• Can develop intake buzz

• Pressure loss from required particle filter

• Loss and distortion from ducting to engine

• Unsteady impact of rotor blades on filter inflow

• Asymmetric „one- sided“ entry of flow to compressor inlet face

• Total pressure recovery (<1 due to losses) varies with Ma and AoA

• Static pressure rise coefficient

• Static pressure rise efficiency

1. False

2. True

3. True

4. False (There is a suction on the lip however)

   
   

1. Temperature increase in the intake due to condensation:

-> Degradation of the thermodynamic cycle

2. Temperature drop in the compressor due to evaporation:

→ Improvement of the thermodynamic cycle

Combination of both effects give a small change in engine overall thermal efficiency, positive or negative

Compressor surge:

• Ice debris released from surfaces causes compressor surge, hence reduction of rotational speed and massflow

Combustor extinction:

• Pieces of ice cause the flame to quench

Engine damage:

• Pieces of ice damageindividual or full rows of aerofoils

The sum of all operating points

Choking of the compressor

At lower speeds the compressor delivers less pressure ratio, therefore also a lower density ratio.

The gaspath in the engine converges and is too tight for the less dense gas in the back -> Acceleration of the flow in the back

In the front the gas path is too big for the dense gas, therefore the velocity goes down and these stages are prone to stall.

When the compressor reaches the surge line it, the flow detaches from the airfoils. The compressor cant deliver the required pressure and the higher pressure in the back of the engine accelerates to the front. After the gas is expelled out the front, the flow attaches to the airfoils and the compressor can deliver pressure again…

• Incompressible working fluid

• Adiabatic and inviscid flow

• Fully pressurized and rotationally symmetrical impeller (Blade nr. = ∞)

• Gravitational influence is negligible

De-Haller Number:

Max. feasible diffusion → Condition to avoid separation at the hub & shroud:

• DHRotor = w2/w1 ≥ 0.7

• DHStator = c3/c2 ≥ 0.7

Diffusion Factor:

Max possible deflection → Conditions to avoid separation on the profile:

• DFRotor = Δwu/u ≤ 0.5

• DFStator = Δcu/u ≤ 0.5

• Performance cycle (Low PR should be achieved with low speed)

• Aerodynamics (Mach no., loss, stability; all these get non-linearly worse when tip speed goes up)

• Structural strength (High tip speeds cause high weight of drum and casing)

• Noise (Noise emission regulations impose different needs for different fan sizes)

1. False

2. False

3. True

4. False

Softwall fan casing:

• Made from aluminum alloy, over-wound with dry aramid fibers

• Energy-absorbing capability, blade get stuck in the fibers

Hardwall fan casing:

• Made from aluminum alloy only and designed to reflect the blade back into the engine

• Enables building in a smaller radial envelope

• Can cause secondary damage well in excess of softwall design

Innovation:

• Use of ductile carbon-fiber reinforced polymer

1. True

2. False

3. False

4. True

Subsonic Sections (Ma1rel < 1) :

• Static pressure rise is achieved through continuous diffusion in the blade passage

• Strong degree of turning required

Supersonic Sections (Ma1rel > 1) :

• Shocks increase pressure, either a strong normal shock appears or multiple weaker oblique shocks

• Continuous diffusion through the remaining rear part of the blade passage

• Little turning required, shock achieves most of the overall pressure rise

• Lowest losses

• Operation at high altitude (low Re number) changes boundary layer state

• Dominating source of loss and potential flow instability is the interaction between the passage shock and the suction side boundary layer

• Boundary layer instabilities may occur, resulting in poor fan performance or vibrations

1. True

2. True

3. False

Buzz saw noise:

• Supersonic flow allows pressure surges on the fantip

Rotor Stator interaction:

• Interaction of the wakes of the Rotor with the front edges of the stators

Nozzle+Mixing (Civil, Low BPR):

+Reduction in noise

+Thrust improvement

-Long nacelle, bypass duct

Separate Jet/Nozzle (Civil, High BPR):

+Short nacelle, bypass duct

+Lower impact of nozzle on fan and core throttling

-No Thrust improvement

-No noise suppression

Variable Nozzle (Military):

+Thrust vectoring

+Used for afterburner

- Long arrangement

-High impact of nozzle on core throttling

1. False

2. False

3. True

4. False

• Secondary Air = Air mass flow that do not primarily contribute to the thrust generation

• „Build and Forget“- System, i.e. the system is installed and must function without any control or external intervention. However it can and must be controlled via measuring points

Air extraction at the housing:

• Direct air extraction at the casing -> aerodynamic effects on the compressor

Air extraction at the outlet:

• Combustion chamber and first turbine stage can only be cooled by this air (pressure has to greater than at the needed location)

Air extraction at the hub:

• Vortex reducer necessary

Wall Injection:

+Simple manufacturing

+Good penetration in the nearfield

-Mixing in main stream insufficient

-High pressure loss

Step Injector:

+Minimal pressure rise(Area higher)

+Recirculation zone(flame holder)

-No wakes in logitudinal direction

-H2 stay near channel bottom

Cavity Injector:

+cavities can anchor and stabilize flames

-high thermal stress

-in total small exchange with the surrounding area

Swept Ramp Injector:

+better wake prudction -> better mixing

-relatively high total pressure loss

Ramjets:

Convergent-Divergent Nozzle

Subsonic->Supersonic

Scramjet:

Purely Divergent Nozzle (Mostly SERN, due to high expansion ratios)

Supersonic->Supersonic

Advantages:

• Expansion self adapting to ambient pressure

• Weight saving

• Large scale integration

Disadvantages:

• Pitching moment

No direct measurement of thrust, due to complex, heavy & costly designs

N1C:

+N1-Signal is in any case available for the control system

+The Fan-inlet temperature as well

-N1C vs. Thrust is a nonlinear function

-The relation between thrust and fan speed changes by fan degradation

→ New Trim Procedure !

EPR:

+Due to the direct correlation of nozzle pressure and thrust there is no need for additional trim procedures

+N1C is a redundant signal

-An additional reliable and precise pressure measurement is needed

-For EPR instead of IEPR only the bypass flow is considered

Full authority digital engine control

The engine load depends on:

• Rotor Speed

• Pitch Angle

• Air Density

Measurement Value:

• Pitch Angle Signal

Advantages:

• Leakage up to 70% less than labyrinth seal

• Compensation of moving sealing gaps, e.g. rotor movement

• Insensitive to shock and pollutant

• Damping effect

• Simple and fast replacement

Application Limits:

• Max. pressure difference: 1500 [kPa]

• Max. temperature: 700 [° C]

• Max. sliding speed: 400 [m/s]

• Only one rotating direction

Pro:

• Enhanced cycle efficiency

• Potentially lower IR-signature

• In some cases crucial component for new concepts

Con:

• Additional pressure losses

• Additional mass

• Rather big dimensions

• Lifetime considerations

• Additional cost

Advantages:

• Increase effective temperature difference (since (nearly) constant temperature on phase-changing side)

• Reduce the required size of the heat exchanger (due to very high heat transfer on phase-changing side)

• Reduce the fluid content on the phase-changing side (reduce mass)

Disadvantage:

• Complex modeling and operation of two-phase flow

• Potential instabilities

• Pressure loss on phase-changing side tends to be rather high

• Accuracy of available correlations quite low

Danger for the combustion chamber : „flame-out“

Bleed of Valves in the MPC are opened during deccelerataion to avoid surging

• Limited by TET (Tt4)

• High Thermal Stresses and gradients in temperature lead to limited cycles

• Highest aerodynamic loads on the engine

• Engine runs at maximum rpm

• High axial and circumferential velocities within the engine place this flight state at the edge of the components’ operability at the choke boundary

• Usually beginning of cruise (loss of weight results in lower thrust requirement)

• Most time is spent in cruise (engine is optimized for these conditions)

• There are two idle states: Ground Idle & Flight Idle

• Lowest states, in which a safe operation is assured

• Limiting is the aerodynamic stability in the components (safe distance from the surge line) and flame stability in the combustor

• At ground idle, the rpm is usually at 25%-50% of N1 and around 60% N2

• At flight idle, the rpm is even higher than at ground idle due to lower density

Aero-elastic phenomenon resulting from coupled interaction of aerodynamics and a flap or torsional mode of the fan blade

-> self-excited high-amplitude vibration

-> Can lead to HCF

-> increased risk of flutter on blisks, since the mechanical damping is lower

N1:

+N1-Signal is in any case available for the control system

+The Fan-inlet temperature as well

-N1C vs. Thrust is a nonlinear function

-The relation between thrust and fan speed changes by fan degradation

EPR:

+Due to the direct correlation of nozzle pressure and thrust there is no need for additional trim procedures

+N1C is a redundant signal

-An additional reliable and precise pressure measurement is needed

-For EPR instead of IEPR only the bypass flow is considered