Introduction to airbreathing propulsion systems Integrated project: AIAA aircraft design competition 1er master Aerospace 2020 Koen Hillewaert, Université de Liège Design of Turbomachines, A&M [email protected] Remy Princivalle, Principal Engineer, Safran Aero Boosters [email protected] 1. Balances, thrust and performance Drag / thrust definition 1. Balances, thrust and performance Airbreathing engines: acceleration of (clean) air mass flow ● Thrust = acceleration force of engine mass flow from flight vf to jet velocity vj ● Powers – Propulsive power → airplane acceleration : – Mechanical power → fluid acceleration : – Lost power ● Propulsive efficiency: ● Increasing propulsive efficiency for constant thrust – increase mass flow, decrease jet velocity – Ingest flow at speed lower than flight speed 1. Balances, thrust and performance Airbreathing engines: Boundary Layer Ingestion ● ● 1. Balances, thrust and performance Airbreathing engines: classical performance parameters ● Thermal energy ! = mf Δhf – Fuel mass flow rate: – Fuel to air ratio: – Fuel lower heating value: ● "verall efficiency propulsive power Pp versus thermal energy ! – Propulsive efficiency: – Thermal efficiency: ● Efficiency $ Thrust specific fuel consumption (TSFC) ● Compacity $ Specific thrust 2. Jet engines Generation of high” speed "et through e#pansion over no%%le Snecma/'' (lympus 593 Afterburning ,urbo"et -./ Leap -i$il ,urbofan Snecma /88 Afterburning Turbofan 2. Jet engines Generation of high” speed "et through e#pansion over no%%le ● Ingestion of ma air at flight speed in nacelle – Ram effect: increased total T and p due to relative Mach num!er Mf ● Increase total pressure and temperature – Mechanical : fan – Thermal : gas generator " #rayton – $fter!urning ● #(pansion over e(haust noz)le to ambient pressure – %ho&ed – $dapted 2. Jet engines -ore flow: Brayton thermodynamic cycle ● Thermodynamic cycle – $dia!atic compression ' → ( : – %om!ustion ( → ) : – $dia!atic e*pansion )+, : 2. Jet engines -ore flow : effiency of the non1ideal Brayton cycle ● Parameters affecting efficiency – -veral pressure ratio .-P / : – Tur!ine Inlet Temperature .TIT/" Tur!ine 0ntry Temperature .T0T/ or -veral Temperature ratio: – %ompressor efficiency – Tur!ine efficiency 2. Jet engines -ore flow : effiency of the non1ideal Brayton cycle ● TiT – 1etermines specific wor& – Limited !y material resistance – 2 '345 K 77 ',55 6 .fusion/ – Re8uires film cooling ● ● "P* – 1etermines efficiency – -ptimum 2 TiT 9 efficiencies – )5 : ,5 2. Jet engines -ore flow : Increasing TiT / Te, 2. Jet engines ,urbo"et : high subsonic through supersonic flow ● %ore flow – $M effect : '’ + ' – %ompressor : ' < ( – %om!ustion : ( < ) – Tur!ine e*pansion : ) – , – 0*haust nozzle jet : , < 4 ● +igh specific thrust 2. Jet engines 23) Afterburning turbo"et: dry and wet operation ● Core flow – Ram effect : '’ - ' – %ompressor : ' < ( – %om!ustion : ( < ) – 0*pansion in tur!ine : ) < , – ,et - afterburning : , < ,; – 0*haust !y adjusta!le nozzle : ,; – 4 ● .early double thrust in /wet0 operation 2. Jet engines -ivil turbofan : high subsonic/transonic ● Core mc and bypass mb flow rate – #ypass ratio .#P /: α > m!".m!?mc/ ● Core / primary mech. power – Fan ? compressor : ' - ( – %om!ustion : ( + ) – Tur!ine → fan 9 compressor ) - , – 0*haust jet : , < 4 ● Bypass - secondary flow thrust – %ompression !y fan ' < (; – 0*haust no==le (; - 4 ● +igh propulsive efficiency: small acceleration of high mass flow rate 2. Jet engines -i$il turbofan: multispool turbofans ● "ptimal rotation speed = slightly supersonic at the tip ● 1ifferent spools / shafts $ optimise rotation speed ● LP spool drives fan $ large LP turbine 2. Jet engines -ivil turbofan : geared turbofan (G,.) PW''55A #PR = '(B4 %FM Leap #PR = C B. '' 2. Jet engines Afterburning turbofan: subsonic to supersonic flight ● *am effect 1’ - 1 ● %ore - primary flow – LP + DP %ompressor : 1 – ( – %om!ustion : ( – ) – 0xpansion in tur!ine : ) – , ● Bypass - secondary flow 5below 16 – LP compression – %ooling of core ● 7i(er-Afterburner – Mantle cooled !y perspiration secondary flow – Mixing of primary and secondary flow – .$fter!urning/ ● #(haust by adjustable no))le 93 – ; 2. Jet engines 234 'AM/&cram5et: supersonic flight M > + ● Cycle without machines – %onvert &inetic energy va in pressure Pt !y E $MF effect : ' - ( – %om!ustion : (+) ● *87'ET : subsonic com!ustion ● <upersonic %om!ustion *87'ET – 0*pand in no==le to form jet : ) < , 2. Jet engines -ombined afterburning turbo"et 7 ram"et 2. Jet engines 8o%%le ● 'et engine no))le = de 2aval no))le – Go==le pressure ratio – %ritical pressure ratio 2 cho&ing – %ho&ing mass flow rate ● Thrust for imperfect e(pansion ● 7a(imal thrust if adapted (pj = pa6 ● #ngine operating point = match >> and no))le – AA determines pH and TH upstream of no==le – Go==le limits ma*imum mass flow rate – Thrust can !e optimi=ed !y varying throat .and e*pansion ratio/ – $rea needs to !e varia!le to accommodate large variations in TH 2. Jet engines 8o%%le ● %onverging – Ionic jet (wrt exhaust T/ → lower speeds – %hoked if GP 7 NP J – $dapted if NP < GP J – Fixed for civil tur!ofan .this could change .BB/ – Lariable throat for military/after!urning tur!ofan ● %onverging4diverging – Digher speed range – Lariable throat and e*pansion area to adapt to AA and flight – .thrust vectoring/ – $fter!urning tur!ojet"tur!ofan 3. Propellers Mechanical acceleration by lift forces on propeller blades 3. Propellers Global operation: 'an9ine-Froude theorem ● 8ccelerating / contracting stream tube ● Thrust ● Propeller = actuator dis@ : pressure jump ● .o losses up-down - Bernoulli 3. Propellers Global operation: 'an9ine-Froude theorem : induced velocity ● Induction factor a ● Thrust computed two ways – stream tu!e control volume – pressure difference 3. Propellers Global operation: thrust, power and propulsive efficiency ● Thrust ● Power ● Propulsive efficiency 3. Propellers 2ift and drag forces on an airfoil Blades : airfoil lift/drag polars 2 w 1 β 2 w 1 β 3. Propellers Blades – layout and operating parameters ● >eometry – Tip radius t – . adial distri!ution of/ !lade profile – Radial distri!ution of chord %.r/ " Iolidity σ(r) = N C(r)/2 r) =NC(r)/2)C(r))/2 ● "perating parameters ξ – &tagger or pitch angle ξ – Rotation speed Ω → local blade speed u = Ω r) =NC(r)/2 – Advance ratio M > va"ut > va"Ω r) =NC(r)/2t u v 3. Propellers Propeller forces 5Blade Element 7ethod6 Blades : forces on blade element section ● Induction factor a $ v51Aa) ● *elative velocity w, flow angle β C 2 ● 2ift/drag forces 2 B 1 as a function of T ξ – elative velocity w 1 – Incidence i = ξ - - β ● %ompute thrust T and tangential force C w u β ● *ecompute induction factor a from T v v(1+a) 3. Propellers (peration: performance parameters ● Thrust coefficient ● Power coefficient 3. Propellers Propeller: force balance (perating point % 2 T 1 ξ w u β v(1+a) 3. Propellers (peration point: variation of advance ratio (flight speed or rotation speed) % 2 T 1 ξ w u β v(1+a) 3. Propellers (peration: pitch control % 2 T 1 ξ w u β v(1+a) 3. Propellers -ontrol ● 7eans of control – 0ngine power " rotation speed : T 2 n(, P 2 n) – $dvance speed vs rotation speed : Egear bo*F ● Fine pitch 2 low gear : – high thrust at low advance speed : take+off, taxi, BBB – limited flight speed ● %oarse pitch 2 high gear : – low thrust at ta&e-off – higher air speeds ● Propeller types – Fi*ed pitch " ground adjustable 2 single gear – Lariable pitch propellers ● Inflight adjusta!le: change throttle and pitch angle independently 2 manual gear !ox ● Fixed velocity: governor adjusts pitch to keep constant rotation speed 2 automatic gear!o* 33 3. Propellers =ower generators ● Internal combustion engine ● >as turbine turboprop B %*"* ● Duture of propulsion systems electric or hybrid, distributed ... 34 4. %hoosing the propulsion system ● Typical cruise speed – Propeller : 5B' K Ma K 5BN – Digh #P tur!ofan : 5BN K Ma K ' – Low BP tur!ofan " tur!ojet : Ma 7 ' – $MM0T : Ma 7 ( – I% $MM0T : Ma 7 4 ● #(tension of operating range of propellers to transonic – .Laria!le pitch tur!ofans/ – Transonic open rotors .% - / – 1ucted fan for hy!rid propulsion 4. %hoosing the propulsion system Future: integrated / hybrid / distributed propulsion systems > Nasa .?(.