siemens digital industries software achieving virtual

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.

siemens.com/software

https://www.sw.siemens.com/en-US/

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

SIEMENS DIGITAL INDUSTRIES SOFTWARE 2

White Paper – Achieving virtual integration of aircraft engine systems

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.



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.



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



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.



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



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).



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.



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



About Siemens Digital Industries Software

Siemens Digital Industries Software is driving transformation to

enable a digital enterprise where engineering, manufacturing

and electronics design meet tomorrow. Xcelerator, the compre-

hensive and integrated portfolio of software and services from

Siemens Digital Industries Software, helps companies of all sizes

create and leverage a comprehensive digital twin that provides

organizations with new insights, opportunities and levels of

automation to drive innovation. For more information on

Siemens Digital Industries Software products and services, visit

siemens.com/software or follow us on LinkedIn, Twitter,

Facebook and Instagram. Siemens Digital Industries Software –

Where today meets tomorrow.

siemens.com/software

© 2021 Siemens. A list of relevant Siemens trademarks can be found here. Other trademarks belong to their respective owners.

83765-D4 6/21 K

Siemens Digital Industries Software

Americas: 1 800 498 5351

EMEA: 00 800 70002222

Asia-Pacific: 001 800 03061910

For additional numbers, click here.

https://new.siemens.com/global/en/general/contact.html

https://www.sw.siemens.com/en-US/

https://www.linkedin.com/company/siemenssoftware/

https://twitter.com/siemenssoftware

https://www.facebook.com/SiemensDISoftware

https://www.instagram.com/siemenssoftware/

https://www.plm.automation.siemens.com/global/en/legal/trademarks.html

siemens digital industries software achieving virtual

Documents