A REAL-TIME SIMULATOR OF A TURBOFAN ENGINE
Jonathan S. LItt
Propulsion Directorate
U.S. Army Aviation Research and Technology Activity - AVSCOM
Lewis Research Center
Cleveland, Ohio 44135
and
John C. DeLaat and Walter C. Merrill
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
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SUMMARY
A real-time dlgital simulator of a Pratt and Whitney FIOO engine has been
developed for real-time code verification and for actuator diagnosls during
full-scale engine testing. This self-contained unit can operate In an openloop
stand-alone mode or as part of a closed-loop control system. It can also
be used for control system design and development. Tests conducted in conjunction
with the NASA Advanced Detection, Isolation, and Accommodation program
show that the simulator Is a valuable tool for real-time code verification and
as a real-tlme actuator slmulator for actuator Fault diagnosis. Although currently
a small perturbation model, advances in microprocessor hardware should
allow the simulator to evolve into a real-tlme, full-envelope, full engine
simulation.
INTRODUCTION
The FIOO engine simulator was designed to support the Advanced Detection
Isolation and Accommodation (ADIA) FIOO englne test. The objective of the ADIA
engine test was to demonstrate the application of analytical redundancy to the
detection, isolation, and accommodation of englne sensor failures (ref. l).
That is, to show that the engine can continue to be controlled accurately -
even during transients - with one or more of the engine sensors giving false
readlngs. The obJectlve of this engine test was also to demonstrate that the
ADIA software works on a real engine and is, therefore, reliable and useful in
a real environment. This software had already been successfully tested on a
hybrid computer simulation of the engine (ref. 2). Due to the usual uncertainties
associated with a full scale engine test, it was determined that should
changes to the control computer's software be necessary, a simulation of the
englne would be requlred for software verlflcatlon. The simulator which has
been developed is a portable box which could be taken into the Propulsion Systems
Laboratory (PSL) to verify any changes in the control interface and monitoring
(CIM) unit's (ref. 3) software before the CIM unit was used to control
the engine. The slmulator was installed in the PSL as shown in flgure I.
Swapping a patch panel allows the CIM unit to control either the engine or the
simulator. This change Is completely transparent to the CIM unlt. This technlque
m|nlmlzes rlsk to the engine whlch mlght otherwise occur if the controller's
software contains a serious error.
The FIO0 engine is a high performance, twin-spool, low by-pass ratio,
turbofan engine. Figure 2 shows the locations of the englne Inputs which are
defined In table I. Figure 3 shows the locations of the engine sensors defined,
along with the other simulator outputs, In table II.
The simulator Is based upon a HYTESS-like model (refs. 4 and 5) of the FIO0
englne wlthout augmentatlon (afterburnlng). HYTESS Is a slmplifled FORTRAN slmulation
of a generalized turbofan engine. To create the slmulator, the orlginal
HYTESS code was revised to incorporate FIO0 specific parameters. Additionally,
the executive was adapted from that of the ADIA code (ref. 6) which executes in
the ClM unit.
This report describes the design and implementation of the FIO0 real-time
portable englne simulator. The report discusses the simplified englne model
and the actuator and sensor models used In the simulator. Next, the design of
the microcomputer implementation, includlng the hardware and software design
details, is described. A user's manual Is included with step by step Instructions
of how to use the simulator. Performance comparisons with the real
englne are presented. Finally, recommendations for future work are given.
MODEL
The originai full nonlinear simulation of the FIO0 engine is a 13 000 llne
FORTRAN program. It incorporates detailed descriptions of both steady-state
and dynamlc engine operation throughout the entire flight envelope. This slmulation
very accurately reproduces the engine's performance but requlres very
large amounts of digital computer memory and processlng time. The HYTESS turbofan
engine simulation was developed to provide a structurally simpler alternative
to engine simulation and thus reduce computer storage and processing
requlrements.
Since the main objective of the sfmulatoF is real-time execution, an FIO0
engine simulation with a HYTESS-Iike structure was used. The HYTESS-IIke model
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