The Boeing Blended-Wing-Body (BWB) airplane concept represents a potential breakthrough in subsonic transport efficiency. Work began on this concept via a study to demonstrate feasibility and begin development of this new class of airplane. In this initial study, 800-passenger BWB and conventional configuration airplanes were sized and compared for a 7000-n mile design range. Both airplanes were based on engine and structural (composite) technology for a 2010 entry into service

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Design of the Blended Wing Body Subsonic Transport

The blended wing body is an aircraft configuration that has the potential to be more efficient than conventional large transport aircraft configurations with the same capability. However, the design of the blended wing is challenging due to the tight coupling between aerodynamic performance, trim, and stability. Other design challenges include the nature and number of the design variables involved, and the transonic flow conditions. To address these issues, a series of aerodynamic shape optimization studies using Reynolds-averaged Navier–Stokes computational fluid dynamics with a Spalart–Allmaras turbulence model is performed. A gradient-based optimization algorithm is used in conjunction with a discrete adjoint method that computes the derivatives of the aerodynamic forces. A total of 273 design variables—twist, airfoil shape, sweep, chord, and span—are considered. The drag coefficient at the cruise condition is minimized subject to lift, trim, static margin, and center plane bending moment constraints. ...

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Aerodynamic Design Optimization Studies of a Blended-Wing-Body Aircraft

A novel domain element shape parameterization method is presented for computational fluid dynamics-based shape optimization. The method is to achieve two aims: (1) provide a generic 'wrap-around' optimization tool that is independent of both flow solver and grid generation package and (2) provide a method that allows high-fidelity aerodynamic optimization of two- and three-dimensional bodies with a low number of design variables. The parameterization technique uses radial basis functions to transfer domain element movements into deformations of the design surface and corresponding aerodynamic mesh, thus allowing total independence from the grid generation package (structured or unstructured). Independence from the flow solver (either inviscid, viscous, aeroelastic) is achieved by obtaining sensitivity information for an advanced gradient-based optimizer (feasible sequential quadratic programming) by finite-differences. Results are presented for two-dimensional aerofoil inverse design and drag optimization problems. Inverse design results demonstrate that a large proportion of the design space is feasible with a relatively low number of design variables using the domain element parameterization. Heavily constrained (in lift, volume, and moment) two-dimensional aerofoil drag optimization has shown that significant improvements over existing designs can be achieved using this method, through the use of various objective functions.

CFD‐based optimization of aerofoils using radial basis functions for domain element parameterization and mesh deformation

The noise goal of the Silent Aircraft Initiative, a collaborative effort between industry, academia and government agencies led by Cambridge University and MIT, demands an airframe design with noise as a prime design variable. This poses a number of design challenges and the necessary design philosophy inherently cuts across multiple disciplines involving aerodynamics, structures, acoustics, mission analysis and operations, and dynamics and control. This paper discusses a novel design methodology synthesizing first principles analysis and high-fidelity simulations, and presents the conceptual design of an aircraft with a calculated noise level of 62 dBA at the airport perimeter. This is near the background noise in a well populated area, making the aircraft imperceptible to the human ear on takeoff and landing. The all-lifting airframe of the conceptual aircraft design also has the potential for a reduced fuel burn of 124 passenger-miles per gallon, a 25% improvement compared to existing commercial aircraft. A key enabling technology in this conceptual design is the aerodynamic shaping of the airframe centerbody which is the main focus of this paper. Design requirements and challenges are identified and the resulting aerodynamic design is discussed in depth. The paper concludes with suggestions for continued research on enabling technologies for quiet commercial aircraft.

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Airframe Design for "Silent Aircraft"

In this paper, it is discussed how knowledge based engineering has been exploited to develop a flexible design system, able to integrate a heterogeneous set of distributed discipline-specific design and analysis tools into a modular design framework. This system, called Design and Engineering Engine (DEE), demonstrated its capability to support designers in performing what-if studies and accelerate Multi-disciplinary Design and Optimisation (MDO), through the automation of those lengthy and repetitive activities typically hampering the design process. Design quality and innovation are also supported by enabling the use of high fidelity analysis tools in the early design phase.

Enabling distributed multi-disciplinary design of complex products: a knowledge based engineering approach

Aerodynamic considerations of blended wing body aircraft

Two-dimensional and three-dimensional contour bumps are designed and optimized for substantial wave drag reduction for an un-swept natural laminar flow (NLF) wing (RAE5243 aerofoil section) at transonic speeds. An NLF aerofoil wing is chosen in this study, as shock con- trol is more crucial for such wings due to the requirement of favourable pressure gradients on a substantial part of the wing. For the validation purpose and to focus on the wave drag issues, the boundary layer is assumed to be fully turbulent from the leading edge. Key bump geometrical parameters including the maximum height, the length, and the crest position have been chosen for the parameterization of the two-dimensional and three-dimensional shock control bumps. For the three-dimensional bumps, an array of the contour bumps is installed spanwise on the transonic wing and their width and spanwise spacing are chosen as additional design param- eters. Both the two-dimensional and the three-dimensional bump shapes are optimized using a discrete adjoint-based optimization method. The performance of the three-dimensional con- tour bumps are compared in detail with the similarly optimized two-dimensional bumps both at and around the design point. The results show that, for the NLF wing studied, the optimized three-dimensional bumps are as effective as the optimized two-dimensional bump in terms of total drag reduction at the given design point, despite the significant difference in their geomet- rical shapes. More importantly, in terms of the operational range for varying lift conditions for practical applications, the three-dimensional bumps outperform the two-dimensional bump by a substantial margin.

Three-dimensional contour bumps for transonic wing drag reduction:

This paper presents aerodynamic studies of a blended wing body (BWB) configuration within an European project, MOB. Firstly, the effects of spanwise distribution on the BWB aircraft aerodynamic efficiency were studied through an inverse design approach, combining both a low fidelity panel method and a high fidelity RANS method. Secondly, the BWB aerofoil profiles were optimised for improved performance. Finally, three-dimensional optimisation of the BWB twist and camber distribution were carried out based on continuous and discrete adjoint approaches.

http://aircraftdesign.nuaa.edu.cn/MDO/ref/Disciplinary%20Optimization/Aerodynamic%20optimization/AIAA-2002-5448.pdf

Aerodynamic studies for blended wing body aircraft

An Euler optimisation for a BWB configuration with winglets incorporating an array of three-dimensional shock control bumps is carried out by employing an efficient adjoint-based optimisation methodology. A high fidelity multi-block grid with over two million grid points is generated to resolve the shape of the 3D shock control bumps, the winglet as well as the overall BWB shape, which are parameterised by over 650 design variables. In order to perform such a large aerodynamic optimisation problem feasibly, the optimisation tools such as the flow solver and the adjoint solver have to be parallelised with a good parallel efficiency. This paper reports the parallel implementation efforts on the adjoint solver; especially on the calculation of the sensitivity derivatives, which has to be looped over the total number of design variables. Results from the optimisation of the wing master sections, winglet aerofoil sections and the three dimensional bumps indicate a significant improvement regarding the aerodynamic performance against the baseline geometry for the given planform layout of the aircraft.

Parallel adjoint-based optimisation of a blended wing body aircraft with shock control bumps

Aerodynamic optimisations of a blended wing-body (BWB) aircraft are presented. A discrete adjoint solver is used to calculate efficiently the gradients, which makes it possible to optimise for a large number of design variables. The optimisations employ either a variable-fidelity method that combines low- and high-fidelity models or a direct sequential quadratic programming (SQP) method. Four Euler optimisations of a BWB aircraft are then presented. The optimisation is allowed to change a series of master sections defining the aircraft geometry as well as the sweep angle on the outer wing for two of the optimisations. Substantial improvements are obtained, not only in the Euler mode but also when the optimised geometries are evaluated using Reynolds-averaged Navier-Stokes solutions. Some interesting features of the optimised wing profiles are discussed.

A. Le Moigne

Papers

Aerodynamic considerations of blended wing body aircraft

Three-dimensional contour bumps for transonic wing drag reduction:

Aerodynamic studies for blended wing body aircraft

Parallel adjoint-based optimisation of a blended wing body aircraft with shock control bumps

Aerofoil profile and sweep optimisation for a blended wing-body aircraft using a discrete adjoint method