Session: 01-01 Conceptual Design and Optimization I

Paper Number: 101426

101426 - Application of a Multidisciplinary Design Process to Assess the Influence of Requirements and Constraints on the Design of Military Engines 

The design of supersonic military aircraft is a complex multidisciplinary optimization (MDO) process in which the dependencies and strong interactions between engine and aircraft must be imperatively considered. Applying a fully coupled propulsion-airframe design system is a highly challenging task, since it requires a set of numerically stable analysis tools being capable of optimizing various design variables. To improve computational efficiency, one currently researched approach is the application of gradient-based optimization techniques that allow to calculate the optima within a reduced design space with the help of analytical derivatives. However, since gradient-based methods are restricted due to local optima and nonconvexity within the design space, some authors have proposed low-fidelity design of experiment (DOE) methods that help to narrow down the selection of suitable combinations of design parameters. This approach allows the division of the multidisciplinary process into subsystems, each of which can be served by specialized engineers. At the same time, interactions between individual disciplines can be taken into account using DOE-based sensitivities. A key advantage of this separation is that the influence of specific variables can be analyzed with higher quality and evaluated for the overall system within each design discipline. The generated knowledge about individual trade-offs improves the corresponding designs of the subsystems and ultimately reduces the number of necessary global iterations.

Following this approach, the German Aerospace Center (DLR) has developed a multidisciplinary design process in which the airframe and propulsion system are designed individually with the aid of DOE-based sensitivities. This publication focuses on the preliminary design of military engines considering the overall aircraft system. The design process is used to investigate the influence of important engine parameters such as overall pressure ratio (OPR), bypass ratio (BPR) and turbine entry temperature (T4) on the design of military aircraft. Furthermore, the impact of thrust requirements and technological constraints of the engine are analyzed.

An important feature of the utilized engine design process is the application of knowledge-based methods to generate a geometric predesign, that is based on thermodynamic cycle simulation as well as geometrical information extracted from cross-sectional drawings of existing engines. In addition, the geometric predesign is combined with published component-based methods that enable an estimation of the engine mass. For an exemplary aircraft design of a Future Fighter Demonstrator (DLR-FFD), we present a variation of OPR, BPR and T4 and investigate their influence on engine size, engine weight and an estimated maximum take-off mass (MTOM) of the aircraft. In particular, stage loading and the resulting stage numbers of individual turbo components as well as their impact on engine weight are highlighted. Furthermore, the influence of the most demanding operating points such as supercruise and combat conditions on the engine design is analyzed. To some extent, the results indicate a clear dependency between the requirements and the choice of the design parameters. The BPR in particular represents a compromise between full load performance and efficiency of military engines. A suitable selection of the BPR is thus a complex optimization task that has to be solved individually for the specified requirements of the aircraft as well as the assumed technology level of the engine. In conclusion, this process and the conducted studies enable the analysis of trade-offs between aircraft and engine designs, thereby allowing a more accurate evaluation of key design decisions for military engines.

Presenting Author: Tomasz Matuschek German Aerospace Center (DLR)

Presenting Author Biography: - Born on September 30th 1993 in Walbrzych (Poland)
- Moved to Leverkusen (Germany) in 2001, finished school in 2012
- Studied Mechanical Engineering 2012 - 2019 at the Technical University of Dortmund with a focus on turbomachinary
- Spent a semester abroad at the Riga Technical University (RTU) in 2018
- Master Thesis at the German Aerospace Center (DLR) in Cologne in 2019 - 2020 researching the preliminary design of afterburners
- Research work on the German Aerospace Center (DLR) in Cologne since 2020, mainly working on performance simulation and predesign of military engines (conventional engines + VCE), future work will also include heat- and power management of military systems

Authors:

Tomasz Matuschek German Aerospace Center (DLR)
Tom Otten German Aerospace Center (DLR)
Sebastian Zenkner German Aerospace Center (DLR)
Richard-Gregor Becker German Aerospace Center (DLR)
Jacopo Zamboni German Aerospace Center (DLR)
Erwin Moerland German Aerospace Center (DLR)