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In-Flight Engine Shutdown and Restart Modeling
5th Propulsion Control and Diagnostics WorkshopOhio Aerospace Institute (OAI)
Cleveland, OHSeptember 16-17, 2015
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Team
• Jeffryes Chapman, VPL• Andy (A.J.) Hamley, GRC intern• Shane Sowers, VPL• Karl Owens, Contractor• Ten-Huei Guo, GRC• Jonathan S. Litt, GRC
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Outline
• Project Background• Simulation Modifications Shutdown• Simulation Modifications Re-Start• Validation• Summary
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Project Background• In co-operation with NASA Langley, there has been an effort
to increase the fidelity of aircraft simulation when one or both engines are operating in the sub-idle region.
• Engine sub-idle modeling facilitates aircraft simulation during in-flight engine shutdown and/or restart
Potential events:• Operation post unrecoverable surge• Combustor blow out• Loss of engine due to
– Bird strike– Fuel loss– Mechanical failure
https://commons.wikimedia.org/wiki/File:PAK_FA_T_50_compressor_stall_on_MAKS_2011.jpg
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C-MAPSS40k Modifications• Commercial Aero-Propulsion System Simulation 40k (C-MAPSS40k)
– All inclusive dynamic high-bypass, dual-spool simulation developed at GRC– Energy balance approach centered around compressor and turbine
performance maps– External solver required for “converging” to a point of operation during any
given time step• Modifications for sub-idle operation
– Extension of performance maps to increase the operational envelope of the engine simulation
– Creation of backup empirical model to offer “fail safe” if simulation convergence can not be achieved.
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Map Extrapolation• Compressor and turbine maps were extended to include sub-idle
operational points– Boundaries: 0 shaft speed, 0 mass flow, and unity pressure ratio– Extrapolation into the paddle and turbine regions of the compressor map was
avoided due to uncertainty of performance resulting from a lack of engine data.
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Integrated Architecture• A Fail-safe model was added to guarantee sub-idle model stability
– Model switching occurs once a criterion is satisfied
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Model Switching
Sub-Idle Check
Nozzle PR Check
Burner Check
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Fail-Safe Windmilling Modeling
• Nc, Nf, and Fnet generated from 2-D table lookups based on Alt. and MN.
Parameters extrapolated from simulated engine data following typical windmilling parameter curves.
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Restart Modeling• A typical start sequence consists of purging/cranking to get to a predefined
speed and clear all un-burnt fuel from the engine• Modeling restart cases:
– Engine is operating on the extrapolated maps• Cranking will occur if windmilling speeds are within specified limits and is modeled by
an external torque on the high pressure shaft. • Re-light will occur once shaft speed exceeds 20% max
– Engine is operating on windmilling tables• Low speed cranking engine model (transfer function) will drive the engine to 20%
shaft speed• Re-light will occur and the model will be transitioned back to the baseline• Cranking will continue as an external torque on the high pressure shaft based on
current shaft speed
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Updating Fuel Control• Shutdown simulated by removing fuel from the engine• Eliminating controller windup:
– PI feedback for limiters removed during blow out– Integration in min limiters removed during start
Integrator eliminated during engine blow out
Integrator eliminated until start has ended
Simulated Burner Lit:Fuel On/Off
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Starter Assist• Torque assist on high pressure shaft at low engine speeds
• Derived from typical crank torque curves• Designed to reduce idle time to roughly 1 min• Increase Stall Margin to acceptable values• Decrease Engine Exhaust Temperature to
acceptable values
SM > 5%
EGT < 1500 R
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Sub-Idle Model Operation
• Engine Simulated Shutdown and Restart at Sea Level Static conditions
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Performance Validation
Figure from Walsh and Fletcher, Gas Turbine Performance, 2 ed
• Validation challenging due to generic nature of model• Comparison to textbook performance and pilot in-flight
performance confirmation
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GRC flight simulation:‐TCM Airframe
‐2 x C‐MAPPS40k Engines
Modeling Platform
EnclosedCockpit
Front CenterView
Front Right
ViewFront Left
View
Right
View
Left
View
Instructor Station
Modular Flight Deck
Scenery & Environment Rendering
Cockpit Rendering & X‐Plane Flight Model
Integrate new requirements into existing NASA Glenn flight simulator
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Summary
• An in-flight shutdown and re-start model was developed and integrated into C-MAPSS40k for use in the NASA Glenn flight simulator
• Two main techniques were used to extend the engine simulation envelope– Performance map extrapolation– Alternate Sub-Idle model fail-safe
• A restart model was created using a two tiered crank simulation– External torque source– Alternate cranking model fail-safe
• Engine control system was adjusted to account for integrator wind-up• Model results show plausible results that allow for smooth transitioning
between engine shutdown and idle.
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References
• Chapman, J.W., Hamley, A.J., Guo, T.-H., Litt, J.S., “Extending the operational envelope of a turbofan engine simulation into the sub-idle region”, AIAA Science and Technology Forum and Exposition, San Diego, CA, Jan. 2016—to appear.