Document
Na tional Aeronautics & Space Adminis tr ation
Dynamic Analysis of the
STARC - ABL Propulsion System
2019 AIAA Propulsion & Energy Forum
Jonathan Kratz and George Thomas
NASA Glenn Research Center
th
August 21 , 2019
8/21/2019 1 2019 AIAA Propulsion & Energy Na tional Aeronautics & Space Adminis tr ation
Outline
Organization
• Background on Electrified Aircraft Propulsion (EAP)
• Background on engine design
• Background on Dynamic System Analysis (DSA)
• Single - aisle Turboelectric AiRCraft with Aft
Boundary Layer propulsor (STARC - ABL)
• Control Development
• Dynamic System Studies
• Energy Storage Consideration
• Conclusion
8/21/2019 2019 AIAA Propulsion & Energy 2 Na tional Aeronautics & Space Adminis tr ation
Electrified Aircraft Propulsion (EAP)
• In recent years there has been an emergence of numerous electrified aircraft --0', concepts, from small to large scale .-- ~ • Leveraging electrification Tilt - Wing Quadrotor Side by Side • Flexibility of where to place propulsors to get an aerodynamic benefit (boundary layer
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~ ingestion, wing tip propulsor ) • Increasing the effective bypass ratio of the propulsion system • Potential to use propulsors for flight control PEGASUS • Adds additional degrees of freedom • Opens up design space • Potential benefits • Improved system efficiency • Reduced noise STARC - ABL • Reduced emissions • Enabling new capabilities for the aircraft *The benefits are only realizable if the concepts are feasible N3 - X 8/21/2019 2019 AIAA Propulsion & Energy 3 Na tional Aeronautics & Space Adminis tr ation
Engine Design
• Engines are designed using system analysis with a focus toward steady - state performance • Steady - state system - level models • Evaluate tradeoffs to optimize the design • Propulsion system design • Objectives: fuel burn, emissions, noise, cost, performance, thrust - to - weight ratio • Constraints: component min/max operating conditions (temperature, pressure, speed, stall margin) • Transients (dynamics) cause the engine to run closer to constraints and the typical solution is to add margin to the steady - state design System • Performance System • Weight Propulsion Propulsion • Cost • Thrust • Fuel - burn Component Component • Weight • Stress • Surge margin
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• Temperature, etc 8/21/2019 2019 AIAA Propulsion & Energy 4 Na tional Aeronautics & Space Adminis tr ation
Dynamic Operation
• Less margin when transitioning • Ideal closed - loop design… ( ) between operating points • Meets 5 second acceleration
*
requirement (takeoff/go - around) • Operability constraints • Has minimal excess margin • Uncertainty stack (off - nominal margin debits) • Controls cannot improve efficiency • Transient stack (how much is needed for a given engine, but can reduce for transients) need for design margin • FAA Requirement is to be able to • Engine designs with extra margin tend accelerate from 15% to 95% thrust to be less efficient within 5 s.
Uncertainty T.O.
, . ----
. ; I ; Time ., Requirement Time ,, Requirement ..
Thrust ,, ..
Op - line J Pressure Ratio Acceptable Idle Acceleration Time Region Surge Margin Corrected Mass Flow Time 8/21/2019 2019 AIAA Propulsion & Energy 5 Na tional Aeronautics & Space Adminis tr ation
Dynamic System Analysis (DSA)
Benefits are only realizable if the concept is feasible Goals: • Evaluate the feasibility of conceptual propulsion systems • Bring the consideration of controls into the propulsion system
, __
r-- design process This entails: AGTF30 C - MAPSS40k • Development of propulsion system controllers • Assessment of dynamic operability • Adjusting of the controller design to assess the trades between responsiveness and operability • Identification of excess operability margin • Inform the propulsion system designers Previous Work: • Commercial - Modular Aero - Propulsion System Simulation 40k (C - MAPSS40k) • Advanced Geared Turbofan 30,000 lb (AGTF30) f • hFan - propulsion system for the Subsonic Ultra Green Aircraft Research (SUGAR) Volt parallel hybrid electric concept SUGAR Volt ( hFan ) Here we consider: • Single - aisle Turboelectric AiRCraft with Aft Boundary Layer propulsor (STARC - ABL ) STARC - ABL 8/21/2019 2019 AIAA Propulsion & Energy 6 Na tional Aeronautics & Space Adminis tr ation
STARC - ABL – The Concept
• Single - aisle tube and wing commercial transport • Capable of producing ~40,000 lb of thrust at sea f level static conditions (SLS)
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• D ucted, electrically driven, boundary layer ingesting tail - cone thruster • 2 underwing engines, each has a 2000 hp generator 3500 hp !ail-cone • A 3500 hp motor to drive the tail fan motor thn1 ste r • Turboelectric (no energy storage ) ge o era t ors • Power is transmitted via a 1000V direct current bus Iil~clrical po» ~r • At cruise ~1/3 of the thrust is provided by the tail transm iss ion ca b le s fan engines 8/21/2019 2019 AIAA Propulsion & Energy 7 tail - cone thruster Na tional Aeronautics & Space Adminis tr ation
STARC - ABL – The Model
• Modeled with Numerical Propulsion System Simulation
(NPSS) code
• Modified to enable dynamic operation and include
health parameters for capturing component
deterioration
• Migrated to MATLAB/Simulink using the NPSS S -
function interface
• Electrical system was modeled simplistically
• Electric machines – 96% efficiency • Inverters – 98% efficiency • Cables – 99.6% efficiency • Each generator supplies half the power to the tail fan motor 8/21/2019 2019 AIAA Propulsion & Energy 8 Na tional Aeronautics & Space Adminis tr ation
STARC - ABL – The Controller
• Controller Inputs: fuel flow ( Wf ), variable bleed valve (VBV), turbofan variable area fan nozzle (VAFN), tail fan VAFN, tail cone thruster motor power • Scheduled based on Mach number (MN), altitude (Alt), and corrected fan speed (turbofan - N1R, or tail fan - NTailR ) • VBV • Turbofan VAFN • Tail fan VAFN • Scheduled based on MN, Alt, and corrected thrust ( FnR ) • Tail cone thruster motor power • Fuel flow is actively controlled w/ net thrust ( Fn ) as the control variable (simplification) Turbofan VBV Tail Fan VAFN VAFN Motor Power Tail Fan Turbofan Net Thrust Wf Net Thrust Fn = 2 × Turbofan Thrust + Tail Fan Thrust 8/21/2019 2019 AIAA Propulsion & Energy 9
Control Development – Overall Strategy
• VAFN control: • Fuel control: • The original model: varied ~78% and • Used the Tool for Turbine Engine Closed - loop ~70% of max area Transient Analysis ( TTECTrA ) controller • The new schedule: varied ~45 % of architecture and design tools max area ( https://github.com/nasa/TTECTrA/releases ) • Tail Fan Motor Limit Logic: • Proportional Integral (PI) controller with • The commanded FnR can change Integral Wind - up Protection (IWP) instantaneously abrupt changes in motor power operability issues • Limit Controllers: • Constructed a limit schedule relating • acceleration & deceleration limiters the tail fan motor power to N1R • maximum high pressure turbine (HPT) inlet • Enforce that the motor power temperature ( T4) command must be within 5% of the • minimum fuel to air ratio (FAR) new schedule *ps3 = high pressure compressor (HPC) static discharge pressure Demand Controller Min Max Actuator Accel NPSS Model Decel 8/21/2019 2019 AIAA Propulsion & Energy 10
Control Development
High Level Thrust/Power Control Logic 8/21/2019 2019 AIAA Propulsion & Energy 11
Controller Development – Accel / Decel
Schedules
FAA Requirement ( Title 14, Chapter I, Subchapter C, Part 33, Subpart E, § 33.73) • the engine must not surge, stall, exceed the maximum operating temperature, or experience any other detrimental factors while the engine is accelerated from minimum rated takeoff thrust to maximum thrust when the power control is moved from its minimum to maximum position in no more than 1 s • the engine must be able to accelerate from its minimum flight idle power level, or from no more than 15% of the rated takeoff thrust, to 95% of the rated takeoff thrust within 5 s • Max RU limiter – limits acceleration Baseline Design Variable: • Mainly guards against HPC stall and over - temperature • Max T4: 3400 ° R • Min RU limiter – limits deceleration • Mainly guards against LPC and fan stall and combustor • Min FAR: 0.01 blow - out due to reduced FAR • TTECTrA has design functions that design the max and • Min HPC SM: 12% min RU schedules • Function of MN, Alt, and N1R • Min LPC SM: 12% • Runs through numerous points in the flight envelope and iteratively runs open - loop simulations which fuel is ramped • Min Fan SM: 10% at varying rates • Searches for a solutions for which the constraints are just met • Min Tail Fan SM: 10% HPC = High Pressure Compressor, LPC = Low Pressure Compressor 8/21/2019 2019 AIAA Propulsion & Energy 12
Controller Development - Baseline Controller
Results
• Model was simulated with aggressive burst & chop transients from idle to max power back to idle SM = Stall Margin Monte Carlo Test Points • Constraints are satisfied • Good response time • Acceptable overshoot • Respects all stall margin and other operating limits • The concept is feasible from a dynamic operation perspective 8/21/2019 2019 AIAA Propulsion & Energy 13
Dynamic Systems Analysis
• Acceleration limit logic was designed for 5 different
minimum HPC SM design values
• The design for 18% SM appears to do the best
Results for a burst transient at sea level static conditions and 27 ° F above the standard atmosphere 8/21/2019 2019 AIAA Propulsion & Energy 14
Dynamic Systems Analysis
• Engine health parameters were varied to build confidence that operability and responsiveness goals could be achieved throughout the life of the system • The design to protect 18% SM remains the best option, meeting the FAA responsiveness requirements and maintaining an HPC SM > ~19% • Allows for as much as a 7% HPC SM reduction at SLS conditions.
• Without a more comprehensive investigation a 3% HPC SM reduction is recommended 8/21/2019 2019 AIAA Propulsion & Energy 15
Energy Storage Consideration
• Consider if STARC - ABL had energy storage • Energy storage could be used to decouple the turbofan engine and tail cone during transient (to some degree) • Tail cone operates the same but a portion of the power supplied to the motor could come from energy storage • Energy storage assists during accelerations power extraction from turbofans decreases naturally faster responding engine acceleration schedule can be relaxed improved HPC operability • During decelerations, more power extraction is allowed from the turbofans improves LPC operability and excess energy can be absorbed by the energy storage devices deceleration transient (chop) acceleration transient (burst) Results for sea level static burst and chop 8/21/2019 2019 AIAA Propulsion & Energy 16 Na tional Aeronautics & Space Adminis tr ation
Conclusion
• Demonstrated a Closed - loop STARC - ABL propulsion
system
• NPSS model integrated with Simulink - based TTECTrA
controller using the NPSS S - function
• Operational throughout the flight envelope
• Dynamic Systems Studies
• Steady - state HPC SM can be reduced by ~3%
• Use of energy storage to “somewhat” decouple the
turbofans and tail cone thruster during transients could
provide some modest operability benefits
8/21/2019 2019 AIAA Propulsion & Energy 17 Na tional Aeronautics & Space Adminis tr ation
Acknowledgments
• This work was funded by the NASA Advanced Air Transport
Technologies (AATT) project under the NASA Aeronautics
Research Mission Directorate (ARMD)
• Thanks go to others at NASA Glenn Research Center who
contributed to this work
• William Haller • Tom Lavelle • Jim Felder 8/21/2019 2019 AIAA Propulsion & Energy 18
Questions
Contact Info:
Jonathan Kratz – jonathan.kratz@nasa.gov
George Thomas – george.l.thomas@nasa.gov
TTECTrA download:
https://github.com/nasa/TTECTrA/releases
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Extra Slides
8/21/2019 2019 AIAA Propulsion & Energy 20
Controller Development - Baseline Controller
Results
• Constraints are respected • Trends are mostly as expected with the exception of the LPC SM • Effects of power extraction are evident LPC behavior 8/21/2019 2019 AIAA Propulsion & Energy 21