European Congress on Computational Methods in Applied Sciences and Engineering ECCOMAS

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mdo system

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Sujets

European Congress on Computational Methods in Applied Sciences and Engineering
ECCOMAS 2004
P. Neittaanmäki, T. Rossi, S. Korotov, E. Oñate, J. Périaux, and D. Knörzer (eds.)
Jyväskylä, 24—28 July 2004
MULTI-DISCIPLINARY OPTIMISATION OF A SUPERSONIC
TRANSPORT AIRCRAFT WING PLANFORM
*
G. Carrier
*
ONERA - Applied Aerodynamics Department
29, avenue de la division Leclerc, BP 72, 92322 Châtillon Cedex, France
E mail: gerald.carrier@onera.fr, web page: www.onera.fr
Key words: Supersonic, High-Speed Civil Transport (HSCT), Multi-disciplinary Analysis
and Optimisation (MDAO), Optimisation.
Abstract. A Multi-Disciplinary Analysis and Optimisation (MDAO) system for the evaluation
and optimisation of the performance of a High-Speed Civil Transport aircraft has been
developed at ONERA within the context of the CISAP project.
This paper first describes the MDO system implemented at ONERA. This MDO system is
constructed by coupling a Multi-Disciplinary Analysis (MDA) process, developed in the
present research project, with different optimisation algorithms including a gradient-based
optimiser and a Genetic Algorithm (GA). The MDA process embeds the different disciplines
modules and schedules and monitors their execution. It is capable of evaluating the global
aircraft performance for a specified mission. Among the different disciplines considered
during the MDA, the aerodynamics and structure disciplines are given special care and
analysed with high fidelity methods, respectively Computational Fluid Dynamics (CFD) and
Finite Element Method (FEM). The other disciplines such as engines performance and flight
mechanics are evaluated with simpler methods.
This MDO system has been applied to optimise two aircraft variants: a Mach 2.0 and a
Mach 1.3 aircraft architectures. The overall objective has been to maximise the aircraft range
while multiple design constraints were considered. The results of these optimisations are
presented in the second part of this paper.
1G. Carrier.
1. INTRODUCTION
The story of civil air transportation has been marked in 2003 by the last scheduled
commercial flight of Concorde. Despite this event, which marks a break in supersonic
commercial transport, a continued interest in High Speed Civil Transport (HSCT) has been
existing in Europe. If the recent European industrial efforts have been mostly concentrated on
large civil transport aircraft, for which a market is clearly identified, HSCT with its reduced
transportation time offers a complementary answer to the continuously developing demand of
commercial air transport. From the experience of a more than 30 years long period of regular
Concorde service, the improvements required over Concorde in term of fuel efficiency and
environmental acceptability to render a second generation HSCT viable are significant,
putting challenging demands on design methodologies to be used in the development of such
an aircraft.
An important knowledge has been consolidated in Europe during the last decades in the
different individual key-disciplines required to design a Mach 2.0 HSCT aircraft. For
instance, in the aerodynamics discipline, wing design and optimisation have been
demonstrated[1] and low-speed performance improvements achieved[2] for a Mach 2.0
aircraft. However, very few researches have been conducted in Europe for Mach number
lower than 2.0, while an interest toward aircraft designs cruising at intermediate Mach number
between 1.0 and 2.0, have recently been expressed by industry. Indeed, choosing a supersonic
cruise speed lower than Mach 2.0 may enable to use existing conventional technologies or, at
least, the less sever operating conditions would facilitate the development of the key
technologies required for HSCT and specific to such an aircraft, such as engine performance
and propulsion integration issues.
In this context, CISAP, a collaborative project between Airbus (AI) and the Association of
European Research Establishments in Aeronautics (EREA), was set-up to investigate the
potential of HSCT aircraft concepts designed for cruise Mach numbers below 2.0 and to
examine the implications for the optimal wing planform of lowering the cruise speed. Such
objectives of new aircraft concepts evaluation require the different disciplines affecting the
overall aircraft performance to be considered through a multi-disciplinary approach. The
Multi-Disciplinary Analysis and Optimisation (MDAO) technology[4] provides an
appropriate method for evaluating and designing aircraft architectures presenting strong
interaction between the different disciplines, such as HSCT[3] and BWB[5] aircraft.
The present paper describes the multi-disciplinary optimisation work performed at
ONERA within the CISAP project. After an introduction of the context of the CISAP project,
the development of the MDAO system for HSCT is described in the second section. The
application of this MDAO system has been made to optimise, first a Mach 2.0 and second a
Mach 1.3 aircraft, and the optimisation results obtained are described in the last section.
2G. Carrier.
2. CONTEXT: THE CISAP PROJECT
CISAP, acronym for “Cruise speed Impact on Supersonic Aircraft wing Planform”, was a
collaborative project between Airbus and EREA. This project was conducted by the Research
Establishments DLR (co-ordinator), NLR, ONERA and QinetiQ, over an 18 months period
running from July 2002 to December 2003.
This project intended to investigate the multi disciplinary effects of changing the cruise
Mach number of an High Speed Civil Transport (HSCT) aircraft, and especially the effect on
the wing planform[6]. Three different cruise Mach numbers were commonly chosen with AI:
M=2.0, M=1.6 and M=1.3.
The research conducted in CISAP was organised in three work packages:
• WP1 consisted in defining the conceptual design of both M=1.6[7] and M=1.3 aircraft
architectures, intended to serve as starting point for the MDO work of WP2. The
M=2.0 aircraft concept was provided by AI;
• WP2 was the main work package and included the development, validation and
application of MDO methodologies by the different partners[8], each partner having
developed its own MDO system on the basis of a common core set of tools;
• WP3 included complementary investigations regarding especially the low speed
performances, alternative structural layout and off design structural behaviour, for one
of the optimised aircraft configuration of WP2.
The next sections of this paper gives an overview of the work performed at ONERA within
WP2 of CISAP.
3. MULTI-DISCIPLINARY OPTIMISATION METHODOLOGY AND SYSTEM
3.1. Optimisation problem formulation
The design/optimisation problem to be solved has been defined as a maximisation problem
of a system(aircraft) level objective defined as the achievable range of an aircraft having:
• a fixed payload of 250 passengers;
• a fixed Maximum Take Off Weight (MTOW) of 340,000 kg.
This problem formulation has been preferred to the alternative of minimising the weight of
an aircraft having the same fixed payload and a minimum achievable range.
3.2. Design variables, constraints and constants
The design space investigated in the present work concerned aircraft design variants
differing by the wing shape and position relatively to the fuselage and also by the altitude at
3G. Carrier.
which the supersonic cruise leg is started. To explore this design space, the MDA procedure is
parameterised through a total of 16 parameters (design variables):
• 7 variables are used to define the wing planform, defined as a double-trapezoidal shape
(Figure 1);
• 6 variables are used to control the thickness and twist in 3 wing sections ( root, crank and
tip sections). Linear interpolations are used in-between;
• 2 variables define the wing position relatively to the fuselage;
• 1 variable is used to control the “start of cruise” altitude (this altitude was actually an
implicit result of the aircraft mission analysis, the actual explicit design variable used
being the angle of attack of the aircraft in supersonic cruise).
A set of system level constraints have been commonly defined and used in this CISAP
project[6]. Different types of constraints can be distinguished:
• geometry constraints affecting wing shape and position to insure that realistic and
realisable geometry of the investigated aircraft designs (minimum thickness at different
wing locations, maximum spanwise wing bending, etc);
• a low speed aerodynamic constraint (stability);
• a trim ability and a maximum angle of attack constraints for the supersonic cruise
condition.
Furthermore, some aircraft/mission specifications were kept constant during the MDO
design optimisations. These parameters can be viewed as design constants or constraints
inside the MDA process. The most significant constants are:
• payload and MTOW (identical for M=1.3 and M=2.0 optimisations, see previous section
for values);
• geometry of the fuselage;
• weights and centre of gravity of the aircraft elements, except the wing weight (but some
equipment weight differ between M=1.3 and M=2.0 aircraft variants);
• maximum allowable stresses in the wing material considered during the wing structure
sizing proces