FP2

Through diffusion in the relative frame of reference (rotor) and the external (?) frame of refernece (stator).

w1>w2, c2>c3

• leakage up to 70% less than labyrinth seals

• compensation of moving sealing gaps

• insensitive to shock and pollutant

• damping effect

• simple and fast replacement

With compressor bleed air the position of the turbine casing can be actively adapted.

When thermal expansion occurs, the clearance control helps keep the clearance constant.

• Started supersonic flow

from left to right

• under-expansion

• adapted expansion

• over-expansion

mir fällt es schwer die Frage zu beantworten…

• After a normal shock, you will always land back on the Fanno line

• more entropy production for stronger shocks (stronger deceleration)

• Additional drag is generated at lower flight Mach number

• Single-Stage-To-Orbit (SSTO)

• Two-Stage-To-Orbit (TSTO)

-> increase fuel consumption and therefore higher TET

measured variables:

• rotation speed

• pressure

• Temperature

• Stroke and Angle

• Torsion

• Weight flow

• Vibration

  …

disturbance variables:

• Air inlet condition

• Exhaust ambient condition

• Mechanical power extraction

• Bleed air

• Geometry Alternations

• Fouling process

• friction

  …

climb rate > 0,3 %

Power Reverse

Max Take-Off

Max Continous

Max Climb

Max Cruis

Max Reverse

Flight Idle

Ground Idle

Reverse Idle

1.) No, all shocks are oblique -> Ma > 1

2.) Yes, after the vertical compression shocks

3.) Only in the strong case.

Reference Lecture 4, p.31-32

only for strong solution: point where three shocks meet

Flow goes across two oblique shocks or across the vertical shock.

-> After the shocks there are two flow areas:

• inner path is subsonic

• outer path is still supersonic

• divided by slip line (SL)

Extracting as much energy as possible through the turbine while keeping high enough exhaust velocity to avoid exhaust gas ingestion

Temperature increase in the intake due to ingestion of exhaust gas -> inefficient operation

effect more pronounced at lower power setting due to the lower exhaust gas velocity

half as large

Civil Subsonic Flight:

• Simple convergent core and bypass nozzle, fixed cross-sectional area

• Thrust reverser unit(TRU)

• Often combined with mixer for noise reduction and thrust increase

• Cross-sectional shape: circular or annular

Military Supersonic Flight:

• Laval nozzle for supersonic exit flow

• Massflow/thrust control by variable throat area

• Variable exit area to adapt to ambient conditions

• Often combined with thrust vectoring

• Integrated thrust reverser unit(TRU)

Softwall fan casing:

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

• blade goes through alloy but stopped and contained by the fibers

Hardwall fan casing:

• Made from aluminum alloy -> diameter reduction

• reflects the blade back into the engine -> may still go through engine causing secondary damage

Innovation: for both designs

• ductile carbon-fiber reinforced polymer

• Reinforcement consists of a triaxial braid

• may achieve up to a 40% weight saving over a metal

• Reduces weight down to less than 50% of metal parts

• Lighterblades >> lighter disc and casing

• Process: 3D woven carbon fibre matrix, trimming, forming, moulded resin injection, machining, surface finishing

• Supply engine with sufficient massflow

• Convert velocity to static pressure (kinetic to potential energy) at convenient Mach number at the fan face

• Allow low inner and outer total pressure losses

• Supply (sufficiently) uniform inlet flow profile to the fan (pressure, temperature, velocity)

• 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 distortion to fan and compressor at high incidence or cross-wind (moderate aerodynamic interaction of intake and compression components)

supersonic flight intake:

• sharp edges, long arrangement, potentially variable

• 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, i.e. violent fluctuations in pressure and related shock system

• work coefficient: Ψ=Δh_t/(u^2/2)

• flow coefficient: φ=c_m/u

• throttling: loading (work coefficient) increases for all stages, higher increase in rear stages

• dethrottling: loading decreases for all stages, higher decrease in rear stages

Reason: mass flow is reduced, therefore the specific work and pressure ratios increase

• reduction: front stages are loaded, rear stages are unloaded

• increase: front stages are unloaded, rear stages are loaded

Reason: check ich nicht

• Specific thrust, thrust-to-weight ratio

• Specific fuel consumption

• Reliability

• Noise

• BPR and fan diameter increasing

• Bypass PR reducing

• Core size reducing

• Jet velocity reducing

• 1% fan efficiency -> 0.7 – 0.8% SFC !!

• Gear

• Noise reduction

-> requirements rather than pure scaling

• Performance cycle

• Aerodynamics

• Structural strength

• Noise

Coefficient for the maximum possible deflection

• low internal and external flow losses

• uniform flow, pressure and temperature distribution for the fan

• noise reduction

• yaw

• pitch

• crosswinds

• extreme flight maneuvers

• passive Helmholtz-resonance liner of the casing

• compromise between acoustically optimised (inlet longer at the bottom) and aerodynamically optimised (longer on top) inlet shape

• icing: debris can enter the engine and cause surging, flame-out and damage

• foreign object damage

• for M<=1.5: vertical shock concepts

• for M>1.5: multi-shock concepts: one or more oblique and one vertical shock

• Increase the number of shocks as much as possible

• all shocks should have a similar pressure ratio

subsonic:

• rounded edges, short

• low static pressure rise and total pressure loss

supersonic:

• sharp edges, long, potentially variable geometry

• high static pressure increase and total pressure loss

• supersonic flow at blade tips (Buzz saw noise BSN)

• Interaction of rotor wake with front edge of stator (Rotor stator interaction RSI)

They shift the operating line towards the surge limit

-slow flight: thick profile with large nose radius allows the stagnation point to move and reduces risk of flow separation -> reduced internal losses

-fast flight: large radius increases local overspeed due to deflecion -> external losses from shocks

-compromise:

• retract lower inlet edge

• thicker profile on underside

• slim profile on upper lip

Mass flow through the blade cascade can’t increase further because Ma=1 is reached in the smallest cross-section

• supplying the engine with air mass flow at all operating conditions

• lossless conversion of kinetic energy to static pressure

  (Ma at fan: 0.4 to 0.6)

Coefficient for the maximum feasible diffusion

• rotor: w2/w1>0.7

• stator: c3/c2>0.7

self-excited high amplitude vibration

• can lead to blade loss

• changes pressure field -> shocks are pushed inside the blade passage and outwards

Flutter guidelines:

• 4-6% flutter margin (to cover threats)

• no flutter after FOD / bird strike

• 3-5% residual stall margin

Fan:

• Fan Blade-Off Simulation

• Fan Blade-Off Containment Model

Bird strike

• Fan Bird Impact Simulation

Pre-swirl reduces the difference in circumferential speeds and therefore it reduces the work done

1. Temperature increase in the intake caused by condensation heat released:

→ Degradation of the thermodynamic cycle and temperature distortion

2. Temperature drop in the compressor caused by binding evaporation heat:

→ Improvement of the thermodynamic cycle (isothermal compression)

-> only small changes in thermodynamic efficiency. if pos or neg depends on other parameters aswell

1.)

2.)

• Take-off, rotation and climb

• landing

• Cross-Wind at take-off

  
  

3.)

• High Yaw angle

• internal compression (complicated shock systems and regulation, low external resistance)

• external compression (easier shock configuration and control, higher external air resistance)

• mixed compression (efficiient option at Ma>3.5)

Ratio between mass flow absorbed by engine and the maximum possible mass flow of the inlet channel

• laval nozzle for supersonic exit flow

• massflow / thrust control by variable throat area

• variable exit area to adapt to ambient conditions

• often with thrust vectoring

• integrated thrust reverser unit

• cross section shape: optimised for low IR radiation, rectangular + flaps, axisymetrix + variable segments, axisymetric + moving central cone or axisymetric + injector system

2-3% with moderate bypass ratios, max thrust gain at BPR=2

Significant reduction of noise

nozzle

Fixed conical nozzles

• simple, no moving parts, converging exhaust

  -> For subsonic aircraft

Variable nozzles: mostly con-di type

• mostly used in combination with afterburner

  -> Area increase of 50-150%

  -> High jet exit velocity for Ma ~ 2,5

A_min must decrease, or A_9 must increase to maintain efficiency

• discharge coefficient: due to friction and inertial forces, the effective cross section is reduced

• thrust coefficient: leakage, friction and non-axial flow reduce effective thrust

• bucket doors -> hot stream

• cascades -> cold stream

• clam shells -> hot stream

• µ=1: oblique shock on inlet lip -> no overflow

• critical: vertical shock in smallest cross-section

• sub-critical: vertical shock is in front of narrowest cross-section, µ<µ_crit

• super critical: vertical shock behind narrowest cross-section, µ=µ_crit and overflow, should be avoided vbecause engine performance drops

Oscillating movement of the vertical shock in the supersonic inlet from supercritical to subcritical position

-> can damage the engine, especially the compressor

• achieve desired conversion of static pressure to velocity for thrust

• satisfy customer life cycle demand (cooling required)

• minimise length and complexity of ducting and variable geometry mechanism

• simple convergent core and bypass nozzle, fixed crossectional areas

• often with mixers: noise reduction, thrust increase

• thrust reverser unit

• shape: annular or circular

• work coefficient ψ increases

• c and mass flow: decrease

• blade AoA: increases

• load: increases

• surge/stall risk: increases (backpressure increaes)

• pressure ratio: increases

at constant rpms, the compressor is throttled (decreae of mass flow) and de-throttled (increase of mass flow) while measuring the performance

• Fan on LPC shaft -> LPC is efficient at high speeds

• engine is more efficient at high BPR- > large fan area

• => large fan radius and high speed -> supersonic flow at tips

• deceleration through shocks instead of deflection ->small profile curve

• over-acceleration should be moderate to reduce shock strength -> low relative profile thickness ~2%

• highly staggered blades to avoid premature blocking

• crit. mach number: Ma_1,rel,crit: Ma=1 can occur locally

• blockage mach number: Ma_1,rel,sperr: vertical shock in blade cascade reaches the pressure side of the next blade, reduced mass flow cant increase

• unique incidence condition

• prevents ingeestion of boundary layer

• helps position and stabilize shocks

It used the forward speed of the aircraft to compress the air without a compressor

Combination of ramjet and turbo jet engine:

• MA<2.5: operates like a normal jet engine

• Ma>2.5: operates like a ramjet

Allows higher flight mach numbers where decelerating the flow subsonic speeds in the combustion chamber would exceed practical temperature limits due to dissociation effects

• wall injection

• step injection

• cavitiy injection

• swept ramp injection

• “hyper mixer“ ram injector

• central injector

• Ramjet: convergent-divergent nozzle (flow from subsonic to supersonic)

• SCRamjet: pure divergent nozzle->single expansion ramp nozzle (SERN)

advantages:

• open jet boundary -> self-adapting to ambient pressure

  • weight saving

  • large scale integration

disadvantages:

• gross thrust angle not fixed to 0°

  • ->dangerous in off-design conditions

…

• high total enthalpy and pressure

• intake geometry must allow wide range of mach numbers

• “unstart“ of engine must be avoided

• materials must withstand high temperatures

• injector system should allow self-ignition

• minimize total pressure loss

• thrust vector deviation (SERN) must be compensated

• fluid state out of component is fluid state into next component

• mass flow balance

• energy/ power balance

• mechanical coupling: rotational speeds are the same on the same shaft

• automatic start procedure

• steady state power control

• acceleration and deceleration (power modification)

• monitoring and control of operating limits

• prevention of compressor flow instability (surge monitoring)

• termination of surge and return to stable operation

• prevention of flame out

  thrust reversal

• fuel flow

• bleed air

• variable stator vane angle

• nozzle area

• afterburner fuel flow

• thrust reverser setting

since thrust cant be measured directly:

• N1C

  • always available

  • - N1C vs thrust is nonlinear and changes with degradation->need to be adjusted

• EPR (engine pressure ratio=, IEPR (integrated (?) engine pressure ratio)

  • direct correlation between nozzle pressure and thrust

  • - additional reliable and precise pressure measurement is required

  • - for EPR only the bypass flow is considered

• sealing the bearing chamber against air leakage

• provide cabin and de-icing pressure

• cool the combustion chamber

• active gap control and housing cooling of LPT

• sealing against hot gas injection, bearing load control and cooling of the blades and disk of HPT

• sealing and cooling of LPT

• ventilation of cavities to prevent oil accumulation

• minimum air usage for maximum effect

• use of “cheap“ air

• minimization of leakage flow

• reduction of temperature gradient (+10K -> turbine disk service life is halved)

• security against failure

They are sacrifical material and allow the gap to be tighter because brushing up wont damage the turbine components

Behaviour of the engine components in stationary operation, without acceleration or deceleration

Interaction between compressor and combustion chamber -> thermal throttling

1. extraction at housing

   • direction of air through external pipes

   • effects on compressor aerodynamics must be taken into account

   • danger: pipe breakdown

2. extraction at hub

   • usage of vortex reducer to impose a solid vortex to avoid pressure drop due to reduction of the radius

3. extraction at the outlet of the HPC

   • only possible extraction point for cooling the combustion chamber and first turbine stage (only here the pressure is high enough “thanks“ to the pressure loss over the combustion chamber)

• hot gas stream from combustion chamber

• heat is conducted through the blade into the disk

• friction between sealing air and disk

• intake of hot gas from the gas path

-HPC has a higher compression ratio than HPT

->HPC pulls more strongly on the shaft than the HPT

->bearing load balancing required

because otherwise the relative total temperature of the cooling air would be too high. Preswirl reduces the difference in circumferential velocity of the air and the disk and therefore reduces the relative total temperature

• heat shields protect external systems from heat radiation

• cooling air prevents hot gas from entering cavities

• stationary seals are used against leakage flows between stationary components

• straight

• stepped (with honeycombs)

• crocodile (with honeycombs)

1. acceleration of flow via sealing fin

2. diffusion due to flow seperation and isobaric trubulence behind fin

   ->targeted static pressure reduction through turbulence behind fin

   ->slow pressure reduction -> mass flow remains low

CS-25:

• acceleration from low idle to MTO in less than 8 seconds

• deceleration from MTO to 10% thrust in less than 3.5 seconds

• without fuel control: adjustment of HP speed is not fast enough compared to the thermal pressurization (due to the inertia of the high pressure components) -> HPC migrates alon a constant N line towards the surge limit

• with fuel control: controlled injection of fuel allows the HP shaft to adapt and prevent the surge margin from decreasing too much

• load decreases due to the reduced back pressure at still high speeds

• HPC delivers too much mass flow to the combustion chamber, FAR reduces to a point where a flameout is possible

• HPC is significantly more agile than MPC and drains the MPC

• -> MPC is unloaded

• HPC is significantly more agile than MPC

• rapid decrease in HP shaft speed compared to LP shaft

• -> back pressure of MPC increases, MPC is throttled and moves towards surge

• This is particulary risky at low speeds because the MPC working line is flatter than that of the HPC

• Solution: bleeding air behind MPC (Booster blow-off valves) to relieve the MPC

• acceleration: HPC

• deceleration: MPC and combustion chamber

• ICAO: International civil aviation organization

• JAA: joint aviation authorities (europe)

• EASA: European aviation safety agency (EU)

• LBA: Luftfahrtbundesamt

• non-containment of high-energy debris

• concentration of toxic products in the cabin bleed air sufficient to incapacitate crew or passengers

• significant thrust in the opposite direction to that commanded by pilot

• uncontrolled fire

• failure of the engine mount system leading to inadvertent engine seperation

• release of the propeller by the engine, if applicable

• complete inability to shut the engine down

• low temperature starting test

• ingestion of rain and hail

• bird strike and ingestion

• compressor and turbine blade failure

• methane

• methanol

• sustainable aviation fuels (SAF)

• hydrogen (gas turbine or fuel cell)

• boundary layer ingesting engines (reduces drag)

• WET (water enhanced turbofan)

• electric propulsion

Because engines must work in a wide range of conditions

• fluid state at exit equals fluid state at entry

• mass flow balance

• energy/power balance

• mechanical equality (same rot. speed on same shaft)

• Max. takeoff (MTO)

  • highest power and thrust

    • low flight speed <0.2 Ma

    • high ambient pressure and density

• Max. Climb (MCL)

  • highest aerodynamical load on components

    • Ma ~0.75

    • cruise altitude

• Max. Cruise (MCR)

  • beginn of cruise with max. cruise thrust (no weight reduction yet)

    • Ma~ 0.75

    • cruise altitude

  • state with highest thermal efficiency

• Idle

  • Ground Idle: 25-50 % max RPM

    • Ma=0

    • low altitude

  • Flight Idle: higher rpm due to lower density

    • Ma~ 0.75

    • cruise altitude

  • lowest states in which safe operation is possible

Ca. 37%