SIEMENS DIGITAL INDUSTRIES SOFTWARE Achieving virtual ...
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SIEMENS DIGITAL INDUSTRIES SOFTWARE
Achieving virtual integration of aircraft engine systems
Addressing the complexity of future propulsion architectures
Executive summaryThis paper introduces the Virtual Integrated Engine methodology for synergistic integration of propulsion systems with other aircraft systems. The methodology uses consistent processes and leverages tools of the Simcenter™ portfolio from Siemens Digital Industries Software to simulate all systems contributing to aero-engine performance in a single environment. The methodology is well suited to tackle the challenges in the design of future propulsion architectures, such as electrification and thermal management.
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More than ever, the key to deliver aircraft engine
performance improvement relates to its synergistic
integration with other aircraft systems. In other
words, optimizing the propulsion system in isola-
tion will not yield the full potential of innovative
architectures, such as hybrid-electric distributed
propulsion. This higher level of integration cannot
be achieved without consistent engineering tools
and processes. A major challenge is the ability to
simulate all systems contributing to the aero-en-
gine performance in a single environment.
Without this capability, integration issues might be
discovered late in the development process as they
remain undetected by conventional subsystems
unit testing.
Siemens Digital Industries Software delivers this
capability with the Virtual Integrated Engine
methodology. Leveraging the Simcenter portfolio
capabilities, it gives better insights on how the
engine will perform once integrated with the
airframe and other aircraft systems. The engine
models provide the basis for design decisions and
corrective actions sooner than what can be done
through physical testing.
The methodology has been applied to conventional
architectures currently in service, supporting for
instance the troubleshooting of engine driven pump
abnormal operation. But the Virtual Integrated
Engine is particularly suited to support the work
done on innovative architectures. In a context of
electrification for instance, thermal management
aspects become even more critical. An optimized
thermal management strategy will necessarily
involve multiple systems, hardware and software,
and multiple stakeholders across the extended
enterprise. The Virtual Integrated Engine method-
ology offers the tools and processes to deal with
that kind of complexity.
Introduction
The well-established Breguet range equation
(named after the French aircraft designer and
builder Louis Charles Breguet, an early aviation
pioneer) features three kinds of contribution
to aircraft performance: the aerodynamic
efficiency, the propulsive efficiency and
the aircraft’s structural mass. One common
denominator is the propulsion system design.
It means in practice that these three “knobs” are
highly interdependent. This applies even more
in a context of electrification, where an
integrated design process of the airframe
and the propulsion is required to reap all
the expected benefits.
Propulsion integration is the cornerstone of aircraft performance
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Examples of more integrated propulsion
technologies
The statement is well illustrated by the concept
of distributing the propulsive power along the
airframe. With electrified propulsion it is possible
to spread the propulsive elements, such as fans,
jets or propellers, over the airframe. The concept
DRAGON1, shown in figure 1 is an example of archi-
tecture relying on this principle. Distributed propul-
sion can be done in a way that enhances both the
aerodynamics and propulsive efficiency, and at the
same time reduces the required wing area compared
to a conventional configuration. But this promise
to gain on all counts comes at the price of higher
complexity. It introduces cross-coupling effects that
traditional design methods might fail to account for.
Synergistic combinations between propulsion and
other systems are not limited to the aero-propulsive
example. In some commercial aircraft concepts,
such as the Airbus ZEROe turbofan concept2 shown
in figure 2, hydrogen is considered as an alternative
to fossil-based fuel. In such concept the hydrogen
must be stored in its cryogenic form, which adds
complexity to the aircraft design and operation.
But it also constitutes an opportunity. By having
a more advanced integration of the propulsion
systems, designers can take advantage of the
cooling potential of liquid hydrogen to dump heat
coming from other systems on board.
Environmental impact and societal acceptance
of commercial
Figure 1. DRAGON
concept from the
French aerospace
lab ONERA1.
Figure 2. Airbus ZEROe turbofan concept2.
“I am convinced that the use of hydrogen, both in synthetic fuels and as a primary power source, has the potential to significantly reduce aviation’s climate impact.”
Guillaume Faury, CEO of Airbus Group Air&Cosmos, November 27, 2021
Designing aircraft propulsion systems is not only
about efficiency. More than ever, it should be
balanced with the environmental and societal
impacts of commercial aviation. It translates into
more and more stringent regulations in terms of
pollutant emission or noise level. As an example,
the Advisory Council for Aeronautics Research in
Europe (ACARE) has formulated guidelines for
“Flightpath 2050.” It sets a target of 75 percent cut
in CO2, 90 percent cut in NOx and 65 percent reduc-
tion in noise for the aviation industry in 20503.
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Propulsion electrification is an opportunity to do
better. One promising approach is the use of an
electric power boost at takeoff. This strategy not
only reduces the noise level, but also gives more
freedom to size and operate the thermal engine in
a beneficial manner. It can only be achieved with a
well-thought-out operational strategy at the vehicle
level, which justifies the need for better integration.
Reducing noise level also makes a good case for
better aircraft propulsion integration. A significant
amount of noise shielding can be achieved by
blending the turbomachinery inside the aircraft’s
body or using some tail structural elements as noise
barrier.
None of these innovations will happen without
maintaining a high level of safety. New concepts
offer potential improvements. With a more distrib-
uted propulsion, there is an opportunity to increase
the level of redundancy in propulsive power genera-
tion and distribution. Introducing these innovations
to smaller aircraft first, like the eFusion project built
by Siemens eAircraft4 (today Rolls-Royce Electrical),
will help mature technologies and increase public
acceptance.
The path to an operational aircraft
Turning these new concepts into an operational
aircraft is a massive systems engineering under-
taking. The key to success lies in the tools and
processes that will ensure that “the improvement of
one system does not adversely impact the perfor-
mance of other systems or the performance of the
aircraft as a whole5.”
This where the Simcenter™ portfolio, which is an
integral part of the Xcelerator™ portfolio from
Siemens Digital Industries Software, brings value.
Simcenter offers scalable, off-the-shelf systems
models that deliver higher-fidelity simulations,
earlier in the design process. Simcenter discourages
working in silos and helps to solve integration
challenges by capturing various physics in a single
environment. This Virtual Integrated Engine strategy
is detailed in the next section, illustrated with the
engineering challenges it supports.
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Modeling and simulation to foster innovation
The report “Commercial Aircraft Propulsion and
Energy Systems Research: Reducing Global Carbon
Emissions5”, calls for “simulation and modeling
improvement” to deliver on the most promising
research projects in aircraft-propulsion integration.
In other words, the industry recognizes the potential
gains of frontloading systems integration testing,
using modeling and simulation capabilities. To
deliver that vision Siemens Digital Industries
Software offers a complete aero-engine simulation
solution, which address all engineering disciplines
as summarized in figure 3.
Figure 3. The set of capabilities within the Simcenter portfolio
facilitates the virtual integration of all engine systems.
“Newly designed engines are highly optimized at the system level to realize the benefits the incorporated technologies provide5.”
The Virtual Integrated Engine approach
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The Virtual Integrated Engine methodology
offers a structured way to scope, integrate
and manage the simulation models
produced by the different stakeholders.
It leverages the modeling and simulation
capabilities within the Simcenter portfolio
to address the wide range of physical
domains involved. All this work must not
be done in isolation; therefore, the method-
ology offers connections to model-based
systems engineering (MBSE) and product
lifecycle management (PLM) capabilities.
The Virtual Integrated Engine structure
follows the organizational structure of
the engine manufacturer. As an example,
the integration of models can be done
according to the Air Transport Association
(ATA) chapters, as shown in figure 4. By
clearly establishing the interface contract,
it optimizes the model production and
exploitation in the context of the company
or extended enterprise.
The methodology scales with the maturity
of the design, supporting all activities from
conceptual design to in-service support.
To maximize re-usability, a model manage-
ment strategy facilitates the integration of
existing validated models to answer analysis
requests. The predefined higher-level struc-
ture allows a straightforward integration of
existing assets, in the form of validated
models and parameters sets.
Figure 4. Example of a Virtual Integrated Engine model
structured according the ATA classification chapters.
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In addition to improving the core gas turbine components, there is lot to gain by
optimizing other contributing aircraft systems. This is especially the case for thermal
management systems, because they may have a sizeable impact on aircraft perfor-
mance and safety. For example, the bearings of a mid-sized gas turbine reject about
100 kW into the oil. The heat must be dumped in the surroundings, in the fuel or the
environment, to maintain operation within acceptable temperature range. But adding
cooling capacities increases the complexity and the weight of the propulsion system,
as well as the non-propulsive power consumption.
Figure 5. Electrified powertrain cooling strategy assessed with a Simcenter Amesim model.
Thermal management can be a breaking point
As demonstrated in recent research activities6, the way the engine and its surroundings
are cooled directly impacts the operational strategy at the aircraft level. In the case of a
hybrid-electric configuration, taking off solely on electric power could increase oil and
fuel temperature beyond acceptable limits. Consequently, power management systems
on board must adapt the power request from each propulsive element to ensure the
aircraft’s safety at all time.
This design task involves multiple engineering disciplines, as fluids systems, mechanical
systems, thermal transfers and realistic flight conditions must be simulated together. The
Virtual Integrated Engine supports these multidisciplinary modeling activities. It offers a
framework, like the one presented in figure 5, to design a cooling strategy that will both
mitigate the performance penalty and ensure safe operation of the aircraft.
Supporting integration with other aircraft systems
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Solve integration issues by involving risk-sharing partners
The Virtual Integrated Engine approach addresses integration of systems coming from
different partners involved in the aircraft program. Integrating engine-driven pumps (EDP), a
common feature throughout the many types of civil aerospace gas turbine engines, is a good
example (figure 6). They generate the power necessary to operate the various hydraulic
system consumers such as landing gears and flight control surfaces. The integration process
involves at least three stakeholders: the airframer, the engine manufacturer and the pump
supplier. In this context, it is challenging to test the integrated system in flight representative
conditions.
Modeling and simulation at a system level supports de-risking such integration by combining,
in a single environment, models of the different components to be integrated on the aircraft.
This approach reveals potential anomalous behaviors that would not appear in conventional
engine physical testing.
It is how Simcenter helped to find the root causes of cavitation erosion encountered in the
engine-driven hydraulic pumps (EDPs) of a commercial transport aircraft. Once conventional
testing methods had been exhausted, the decision was made to model the complete system:
the EDP together with the engine mounted hydraulic pipes. With simulations of aircraft repre-
sentative flight conditions, designers identified that long sections of rigid pipe combined with
the pump’s actuation strategy was triggering the cavitation erosion in the pump. The results
generated from this modeling activity were validated using iron bird and engine test data.
Figure 6. Engine driven pumps (in pink) connected to the accessory gearbox (in yellow)
and pipework (in brown) of a large civil aircraft engine (Source: Rolls-Royce Plc).
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Evaluate innovative architectures
Variations of the thermodynamic cycle on which engines in commercial
service operate would offer improvement. As it is more commonly done in
ground power plants, additional heat exchangers would improve the
cycle’s efficiency by recovering heat from the exhaust, for example. The
improvement should be balanced with the additional cost and weight of
such heat exchangers. Operability, with reduction in compressor surge
margin for instance, might be a concern as well.
The Virtual Integrated Engine approach supports the evaluation of these
novel architectures. As done in recent studies on rotorcraft powertrain
electrification7, an integrated model, like the one presented in figure 7,
tells us whether the current state of the art of heat exchangers technology
makes the architecture viable.
Figure 7. Recuperated turboshaft engine performance
evaluated within Simcenter Amesim.
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The Virtual Integrated Engine methodology devel-
oped at Siemens Digital Industries Software and
supported by the Simcenter portfolio aims at:
- Creating and managing scalable models according
to the propulsion system’s architecture
- Supporting dynamic simulation of multiple
systems with flight representative boundary
conditions
- Securing and ensuring traceability of models
and data
- Creating architectures for simulation in an open
platform and configurating them for trade-off
studies
- Harmonizing and complementing the transition
towards model-based systems engineering, and the
implementation of its principles
As a result, the complex modeling process is harmo-
nized and secured, and the know-how developed
within the organization is capitalized. Finally, an
earlier integration of the models representing the
engine systems can be achieved, their interactions
evaluated, and different architectures compared.
References1. ONERA, the French Aerospace Lab, June 17, 2019. Online: https://www.onera.fr/en/
news/how-can-we-reduce-fuel-consumption%3F-dragon.
2. Airbus Commercial Aircraft, September 21, 2020. Online: https://www.airbus.com/innovation/zero-emission/hydrogen/zeroe.html.
3. Advisory Council for Aviation Research and Innovation in Europe (ACARE), “Flightpath 2050 Goals.” Online: https://www.acare4europe.org/sria/flightpath-2050-goals/protecting-environment-and-energy-supply-0.
4. F. Anton, “eAircraft: Hybrid-elektrische Antriebe für Luftfahrzeuge,” Siemens AG, Corporate Technology, September 10, 2019. Online: https://www.bbaa.de/fileadmin/user_upload/02-preis/02-02-preistraeger/newsletter-2019/02-2019-09/02_Siemens_Anton.pdf.
5. National Academies of Sciences, Engineering, and Medicine, “Commercial Aircraft Propulsion and Energy Systems Research: Reducing Global Carbon Emissions,” The National Academies Press, Washington, DC, 2016.
6. I. Roumeliotis, L. Castro, S. Jafari, V. Pachidis, L. De Riberolles and O. Broca, “Integrated Systems Simulation for Assessing Fuel Thermal Management Capabilities for Hybrid-Electric Rotorcraft,” in ASME Turbo Expo, 2020.
7. Roumeliotis, T. Nikolaidis, V. Pachidis, O. Broca and U. Deniz, „Dynamic Simulation of a Rotorcraft Hybrid Engine in Simcenter Amesim,“ in 44th European Rotorcraft Forum, Delft, 2018.
Conclusion
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