Challenges of future aircraft propulsion: A review of distributed propulsion technology and its potential application for the all electric commercial aircraft

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

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

This paper presents the work done in designing a morphing wing concept for a small experimental unmanned aerial vehicle to improve the vehicle's performance over its intended speed range. The wing is designed with a multidisciplinary design optimization tool, in which an aerodynamic shape optimization code coupled with a structural morphing model is used to obtain a set of optimal wing shapes for minimum drag at different flight speeds. The optimization procedure is described as well as the structural model. The aerodynamic shape optimization code, that uses a viscous two-dimensional panel method formulation coupled with a nonlinear lifting-line algorithm and a sequential quadratic programming optimization algorithm, is suitable for preliminary wing design optimization tasks. The morphing concept, based on changes in wing-planform shape and wing-section shape achieved by extending spars and telescopic ribs, is explained in detail. Comparisons between optimized fixed wing performance, optimal morphing wing performance, and the performance of the wing obtained from the coupled aerodynamic-structural solution are presented. Estimates for the performance enhancements achieved by the unmanned aerial vehicles when fitted with this new morphing wing are also presented. Some conclusions on this concept are addressed with comments on the benefits and drawbacks of the morphing mechanism design.

Optimization of a Morphing Wing Based on Coupled Aerodynamic and Structural Constraints

A study is presented of the effects of spanwise lift distribution on aerodynamic efficiency for a blended wing body (BWB) configuration of a given baseline planform. The baseline geometry is initially assessed by a high-fidelity aerodynamic model based on a multiblock structured grid Reynolds-averaged Navier-Stokes (RANS) solution. The accuracy of the simulation is investigated by a grid sensitivity study regarding total drag and its pressure drag and skin-friction drag components. Excessive outer wing loading with associated shock wave, hence, wave drag, has been revealed to be the major factor degrading the aerodynamic performance of the baseline BWB model. To relieve the outer wing, an efficient low-fidelity panel method aerodynamic model is used for the inverse design to achieve the target lift distributions through the variation of twist distribution along the span, shifting the load inboard. For the given BWB geometry, the baseline model is retwisted to achieve an elliptic, a triangular, and an averaged elliptic/triangular spanwise loading distribution. The designs are then analyzed using the high-fidelity RANS aerodynamic model. The wave drag component of the total drag for different span loadings is extracted from the flowfield solution to gain insight into the drag reduction provided by the new twist designs

Spanwise Lift Distribution for Blended Wing Body Aircraft.

An improved response surface based optimization technique is presented for two-dimensional airfoil design at transonic speed. The method is based on an iterative scheme where least-square fitted quadratic polynomials of objective function and constraints are repeatedly corrected locally, about the current minimum, by adding the actual function value to the data set used to construct the polynomials. When no further cost function reduction is achieved, the design domain upon which the optimization is initially performed is changed, preserving its initial size, by updating the center point with the position of the last minimum found. The optimization is then conducted by using the same approximations built over the initial design space, which are again iteratively corrected until convergence to a given tolerance. To construct the response surfaces, the design space is explored by using a uniform Latin hypercube, aiming at reducing the bias error, in contrast with previous techniques based on D-optimality criterion. The geometry is modeled by using the PARSEC parameterization

Iterative Response Surface Based Optimization Scheme for Transonic Airfoil Design

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 efficient multi-fidelity optimization methodology for turbofan intake acoustic liners is presented whereby the wall acoustic impedance is used as a design variable, in the frequency domain, to maximize forward fan noise suppression. Two methods are employed to predict the liner attenuation, a low-fidelity method based on solving the duct mode propagation for a treated circular duct with uniform mean flow using an eigenvalue code, and a high-fidelity method based on solving the duct mode propagation and radiation for a realistic inlet and flow using the finite element code ACTRAN. A validation of the prediction methodology is performed using a baseline seamless inlet liner, for which in situ impedance measurements, internal modal measurements, and far-field noise measurements are available. Both methods are then used to create response surfaces of the liner noise attenuation as a function of the liner impedance. The optimal wall impedance can then be extracted from these response surfaces. The speed of the low-fidelity method makes it possible to explore large sections of the design space at each of the target frequencies inexpensively, while allowing identification of wall impedance sub-domains where relative optima can be determined. The high fidelity method is employed on these sub-domains to provide more accurate and complete modeling. An empirically validated impedance model is then used to define a liner construction for a double-layer seamless liner that provides the best match to the optimum wall impedance.

Optimization of a Seamless Inlet Liner Using an Empirically Validated Prediction Method

This paper describes recent research activities carried out by GKN Aerospace and Honeywell Aerospace to design, fabricate and test zero-splice intake acoustic liners. A comparative assessment of the performance of two different zero-splice intake acoustic liner concepts is presented. Demonstrators for a Seamless Single-Degree of Freedom (SDOF) Linear liner and a Seamless Double-Layer Liner were designed and manufactured at GKN Aerospace. Far field static engine noise tests were conducted at Honeywell's Acoustic Test Facility in San Tan, Arizona, to evaluate the effectiveness of the liners and their benefit to aircraft community noise reduction.

http://enu.kz/repository/2009/AIAA-2009-3365.pdf

Armando Vavalle

Papers

Spanwise Lift Distribution for Blended Wing Body Aircraft.

Iterative Response Surface Based Optimization Scheme for Transonic Airfoil Design

Aerodynamic studies for blended wing body aircraft

Optimization of a Seamless Inlet Liner Using an Empirically Validated Prediction Method

Design and Verification of Seamless Intake Acoustic Liners for Business Jet Class Turbofan Engines