Table 1 - uploaded by Timothy Chau
Content may be subject to copyright.
Context in source publication
Context 1
... particular, we are interested in the ratio between friction and pressure drag, and hence size the optimization grid such that this ratio is as close to the grid converged value as possible. An overview of the grids is provided in Table 1. The off-wall spacings in wall units, y + , are based on the flow solutions of the optimized geometries. ...
Similar publications
![Fig. 7 Aerodynamic optimization process [12] coupled with a mission...](profile/Francois-Gallard/publication/333806407/figure/fig4/AS:774088616333312@1561568516992/Aerodynamic-optimization-process-12-coupled-with-a-mission-tool-to-compute-the-COC-The_Q320.jpg)
Reducing noise in mobile applications such as cars, aircrafts and trains is a major challenge for today’s engineers. In most cases, sound sources and sound radiating structures are locally separated. The airborne sound field is a result of the excitation and the transfer through the mechanical system. The resulting structure-borne sound is propagat...
In this work, a novel optimization framework, based on a Multi-Disciplinary Optimization (MDO) procedure, applied to the vibro-acoustic Finite Element Method (FEM) model of an aircraft fuselage mock-up, is proposed. The MDO procedure, based on an Efficient Global Optimization (EGO)-like approach, is implemented to characterize acoustic sources that...
Aerodynamic design optimization is a key aspect in aircraft design. The further evolution of advanced aircraft derivatives requires a powerful optimization toolbox. Reinforcement learning (RL) is a powerful optimization tool but has rarely been utilized in the aerodynamic design. It can potentially obtain results similar to those of a human designe...
Citations
... Such numerical optimization frameworks can provide an efficient and adept tool for assessing the performance of unconventional aircraft, as opposed to designing the complete system, if computational resources are strategically allocated mainly where they provide the greatest accuracy benefit. The included medium-to high-fidelity models enable the potential of unconventional aircraft configurations to be realized in part through design features that exploit complex physical phenomena [5][6][7][8][9][10][11][12][13]. ...
Conventional tube-and-wing and proposed blended-wing-body airliners must satisfy several design requirements, but the latter configuration is tightly integrated and sensitive to these requirements. In this work, blended-wing-body regional aircraft are investigated using a gradient-based mixed-fidelity multidisciplinary optimization framework centered on a Reynolds-averaged Navier-Stokes solver. In addition to sizing and cruise trim, design requirements considered include one-engine-inoperative directional trim, takeoff rotation ability, takeoff field length, initial climb performance, low-speed trim and static margin, and top-of-climb rate of climb. Results show how optimal design features vary and performance is overpredicted if critical design requirements are excluded and how key elements of geometric freedom help realize the potential of the configuration. A 4.8% block fuel burn benefit is enabled by pivot-piston variable-length landing gear even with low-mounted engines and high design freedom. The off-design constraints penalize block fuel burn by 3.2% if variable-length landing gear is considered, but this value reaches 7.6% if geometric freedom that inhibits tight cabin contouring and the formation of a novel forebody ridge is removed. Leading-edge carving is optimal. The high design freedom and high-fidelity aerodynamics model help efficiently satisfy the design requirements, resulting in a cruise lift-to-drag ratio of 21.7 at 36 000 ft and Mach 0.78.
... In Ref. [100], higher fidelity numerical methods were used to assess the aerodynamic performance of the box wing, with the aim of using this information to make a preliminary assessment of fuel consumption and to compare it with a conventional benchmark. Also in this case, the approach used is to design innovation to provide incremental performance gains, with the selection of TLARs in a likefor-like view of the conventional competitor; the TLARs are chosen starting from those of the Embraer E190 aircraft operating in the regional jet sector, i.e. 100 passengers for a design range of 500 nm and a cruise Mach of 0.78. ...
... TW and BW comparative results. Data taken from Ref.[100] ...
This article is intended to introduce an alternative approach to comparative analyses between innovative aeronautical technologies and established state-of-the-art references. Commonly, the tendency is to use a ‘like-for-like’ comparative approach with respect to current technologies -defined as reference benchmarks- that is, to evaluate the possible incremental improvements that can be achieved by introducing a specific technological innovation. However, when innovations that potentially introduce step improvements or new functions compared to the state of the art are evaluated, typically referred to as ‘breakthrough’, this approach may not be the most formally sound one, and it may introduce bias and misjudgements. In the field of aircraft design, using the same top-level requirements and figures of merit as those used for conventional aircraft to initialise and steer the design of unconventional configurations, could undermine the exploitation of their operating and functional potential. The soundness of the comparative approach is of paramount importance, especially in the very early stages of the development of disruptive technologies and unconventional aircraft configurations. In this paper, with the supporting example of the application of the box-wing configuration to medium-range transport aircraft, a general discussion is offered on the necessity of leaving aside the ‘like-for-like’ benchmark approach when investigating the potential of disruptive aircraft innovations. This argumentation does not only refer to the case study proposed as an example, but is generally extendable to aeronautical innovations that may introduce operating and functional novelties compared to current technologies.
... The fin and the unnecessary fuselage length extension lead to a significant wetted area and friction drag penalties, which hinder the induced drag benefits of the concept. Given Prandtl plane concepts are of particular interest for green transport aviation, most recent studies are dedicated to stability issues of large box-wing aircraft concepts [9][10][11][12][13], with extremely few articles about light box-wings. ...
... However, directional stability details are missing in this concept due to it being equipped with a conventional twin tail with large vertical surfaces that ensures enough stability margin at the cost of a significant wetted area. As can be noted from most recent studies [9][10][11][12][13][14][15][16][17][18], longitudinal stability of box-planes has been studied very thoroughly, in particular for heavy transport mission profile at transonic speeds. There is, however, a significant knowledge gap concerning directional stability, especially for a light subsonic box-wing lacking a conventional fin. ...
This study aimed to explore the directional stability issues of a previously studied light box-wing aircraft model with a pusher propeller engine in the fuselage aft section. Earlier configurations have included the use of fuselage together with a lifting system consisting of two wings joined together at their wingtips with vertical stabilizers. However, these side vertical surfaces failed to provide the aircraft with sufficient directional stability, thus prompting the quest in this study for novel solutions that would exclude the need for a fuselage extension and a typical fin. Solutions included the use of a ducted propeller and few configurations of small "fishtail" vertical fins, which formed part of the aft fuselage itself and coupled with vortex generators on the fuselage surface to improve their interference and heal flow separation at the fuselage aft cone. The results of wind tunnel testing were supported with CFD simulations to explain the flow behavior of each of the studied solutions. Tuft visualization and computed flow patterns allowed identification of the sources of the observed low efficiency in terms of directional stability of the fishtail against a simple idle duct without a propeller. A final configuration with a duct and a modified version of the fuselage fins was achieved that provides enough yaw stability margins for a safe flight.
... In this case, for a fixed lift coefficient, the viscous drag of a box-wing is 26% higher than the one of the elliptical wing, whereas a benefit of 46% in terms of induced drag is obtained. This result is in line with previous aerodynamic shape optimization studies of box-wings, in which Euler-based [14,15] and RANS-based [16] approaches have been implemented to minimize drag considering prescribed design variables and constraints. In both cases, the box-wings were able to redistribute the total lift from one wing to the other, satisfying several design constraints, while simultaneously improving aerodynamic performance. ...
... In this case, the fore and aft wings are characterized by wash-out (i.e., decreasing the incidence angle from the wing root out to the wing tip) and wash-in (i.e., increasing the incidence angle from the root to the tip), respectively. The optimized results are consistent with those of past studies and with theoretical results, providing a reliable estimate of the performance of the BW aircraft [14,16]. Figures 10 and 11 illustrate the surface pressure contours and pressure distributions, respectively, across the vertical wing. ...
This paper presents an exploration of the aerodynamic design of a box-wing aircraft concept through high-fidelity aerodynamic shape optimization. The optimization framework consists of B-spline parameterization surfaces, an integrated mesh parameterization and deformation scheme based on the theory of linear elasticity , free-form and axial deformation geometry control, a Newton-Krylov-Schur flow solver for the Reynolds-averaged Navier-Stokes equations, a gradient-based optimizer, and the discrete-adjoint method for gradient evaluation. These modules are integrated in an aerodynamic shape optimization framework called Jetstream, which is used to minimize the cruise drag of a single-aisle, medium range box-wing aircraft at transonic flight conditions (Mach = 0.78) with lift, trim, and minimum wing volume constraints. The drag of the optimized box-wing configuration is about 10% lower than the initial concept due to reduced wave drag from the near elimination of shocks and reduced induced drag from an optimal spanwise lift distribution. These results demonstrate the potential aerodynamic advantages of the box-wing concept, and the importance of high-fidelity analysis and optimization tools towards the development and evaluation of novel configurations that can lead to reduced fuel burn and emissions.
... From the point of view of academic projects, many authors have used low-fidelity [22][23][24]26], medium fidelity [27,28] and high-fidelity [29,30] methodologies to compare the aerodynamic benefits of BW configurations against CTW designs. Despite their obvious differences, mainly regarding aerodynamic modeling and optimization algorithms, the studies have offered useful insight into the basic patterns and trade-offs of the large-scale geometric parameters of a BW design. ...
... For the BW case, sweep values ( Λ ) are determined by the stagger variation so that the fore wing has an aft-swept and the aft wing has a forward-swept while keeping their tips aligned, i.e., the vertical tip fin [3] has zero cant angle. Since the sweep angle has a significant Previous studies on BW concepts have shown the Lift-to-Drag (L/D) ratio improves when height-to-span and staggerto-span ratios increase [16,28,30]. Therefore, the fore wing leading edge station was chosen as a design variable, enabling the BW concept to be compatible with both the fuselage length of the reference aircraft and the current airport infrastructure. ...
Unconventional configurations and innovative propulsion technologies have been continuously developed for reducing both fuel-burn and global net carbon emissions. This article describes an advanced civil transport aircraft designed from the combination of a Box-Wing configuration with a Boundary Layer Ingestion (BLI) propulsion system. A conceptual-level Multidisciplinary Design Optimization strategy provided the main aerodynamic and performance characteristics of the aircraft, based on appropriate design requirements, variables and constraints. For direct performance comparison against a conventional aircraft, a single-point objective function based on minimum block fuel was evaluated by means of low-fidelity aircraft models. Subsequently, a back-to-back Computational Fluid Dynamics assessment of non-BLI and BLI versions of the aircraft was performed. Two major analyses comprised the aerodynamic evaluation: (i) quantification of the BLI benefit using the power balance method, (ii) performance evaluation of the propulsor inlet in terms of the total pressure recovery and the distortion index. The conceptual design results showed the box-wing configuration provided major fuel-burn savings compared to its conventional counterpart. On the other hand, the BLI version reduced engine power requirements at cruise in comparison with the non-BLI version, but decreased the total pressure recovery, resulting in more distortion at the aerodynamic interface plane. The main contribution of this study lies on the potential benefits of such an original unconven-tional configuration, whose technologies increased aerodynamic performance, which reduced fuel consumption and hence carbon emissions.
... The fin and the unnecessary fuselage length extension lead to a significant wetted area and friction drag penalties, which hinder the induced drag benefits of the concept. Given Prandtl plane concepts are of particular interest for green transport aviation, most recent studies are dedicated to stability issues of large box-wing aircraft concepts [9][10][11][12][13], with extremely few articles about light box-wings. ...
... However, directional stability details are missing in this concept due to it being equipped with a conventional twin tail with large vertical surfaces that ensures enough stability margin at the cost of a significant wetted area. As can be noted from most recent studies [9][10][11][12][13][14][15][16][17][18], longitudinal stability of box-planes has been studied very thoroughly, in particular for heavy transport mission profile at transonic speeds. There is, however, a significant knowledge gap concerning directional stability, especially for a light subsonic box-wing lacking a conventional fin. ...
This study aimed to explore the directional stability issues of a previously studied light box-wing aircraft model with a pusher propeller engine in the fuselage aft section. Earlier configurations have included the use of fuselage together with a lifting system consisting of two wings joined together at their wingtips with vertical stabilizers. However, these side vertical surfaces failed to provide the aircraft with sufficient directional stability, thus prompting the quest in this study for novel solutions that would exclude the need for a fuselage extension and a typical fin. Solutions included the use of a ducted propeller and few configurations of small “fishtail” vertical fins, which formed part of the aft fuselage itself and coupled with vortex generators on the fuselage surface to improve their interference and heal flow separation at the fuselage aft cone. The results of wind tunnel testing were supported with CFD simulations to explain the flow behavior of each of the studied solutions. Tuft visualization and computed flow patterns allowed identification of the sources of the observed low efficiency in terms of directional stability of the fishtail against a simple idle duct without a propeller. A final configuration with a duct and a modified version of the fuselage fins was achieved that provides enough yaw stability margins for a safe flight.
... Finally, these BW concepts share specific design characteristics such as a rear installation of the engines and fuselage-mounted main landing gear, which increase fuselage weight, as well as cost and integration complexity. • There are a few works focused on high-fidelity optimization of BW concepts [249,250]. Such works provided a more detailed perspective about its benefits in terms of the geometric arrangement. ...
In recent decades, the environmental impacts of aviation have become a key challenge for the aeronautical community. Advanced and well-established technologies such as active flow control systems, wing-tip devices, high bypass ratio engines, composite materials, among others, have demonstrated fuel-burn benefits by reducing drag and/or weight. Nevertheless, aviation remains under intense pressure to become more sustainable. For this reason, there is a strong drive to explore unconventional aircraft with the aim of reducing both environmental emissions and Direct Operating Cost. This paper presents the current state-of-the-art in the development of future aircraft for civil aviation. The literature review is conducted through an appropriate search protocol to ensure the selection of the most relevant sources. After a brief historical background, progress in the design and development of several unconventional aircraft configurations is presented. Concepts such as Blended/Hybrid Wing Bodies, nonplanar wing designs, next-generation propulsion technologies that are tightly integrated with the airframe, among others, are reviewed. Special attention is given to design methodologies (level-of-fidelity), cruise altitude, aerodynamic performance, and fuel-burn benefits over conventional configurations. The primary contributions of this review are (i) a detailed survey of the design characteristics of unconventional aircraft for non-specialists, and (ii) a comprehensive review of the literature detailing past and current design trends of such configurations for specialists.
... Exploratory design may be considered as a third class of problem or as a subcategory within preliminary design, combining large geometric flexibility with often unknown design spaces, and searching for novel designs. Common examples of exploratory optimization include the study of hybrid wing body (HWB) geometries [3,12], box-wing aircraft [13] or other unconventional designs. In preliminary or exploratory design, aerodynamic shape optimization is often combined with other disciplines as in multidisciplinary optimization. ...
A gradient-based multistart method based on a set of 17 to 33 random initial geometries is used to examine the risk associated with multimodality when applying gradient-based optimization to aerodynamic shape optimization. Aerodynamic shape optimization problems typical of detailed, preliminary, and exploratory design are shown to consistently present design spaces with multiple local optima. In the case of detailed design, the risk of converging to a local optimum with performance significantly inferior to that of the best local optimum found is reduced due to the ability of a well-designed initial geometry, which is often available for such problems, to converge to a well-performing local optimum. In problems permitting increased geometric freedom typical of preliminary design, the risk associated with multimodality is much higher. This risk is further exacerbated in exploratory cases where high geometric freedom is combined with limited knowledge of the design space in question and hence greater differences between available initial geometries and the optimal geometry. Therefore, for preliminary and exploratory design, allocating resources toward addressing multimodality can significantly reduce the risk of overlooking a superior optimum.
... An induced drag evaluation in compressible flow at M ∞ 0.5 was performed in Ref. [14], where the optimal shape of the Box Wing was presented and Euler equations were numerically solved. In Ref. [16], the investigation was further refined by performing an aerodynamic shape optimization of a Box-Wing system for regional aircraft applications. Compressibility effects were included at M ∞ 0.78, and Reynolds-averaged Navier-Stokes equations were considered. ...
... The result indicated that the increase of vertical aspect ratio was preferred by the optimizer, which is a property found also in Ref. [8] for the incompressible inviscid case. Thus, the study [16] was an indirect proof that induced drag is one of the key aspects of the Box Wing for flight conditions well beyond the original ones adopted by Prandtl in 1924 [3], when he first introduced this concept. This is the main technical point addressed by the present contribution: the goal is to precisely assess the relative importance of the different drag components, and it will even go forward to demonstrate that the theoretical predictions made in Ref. [8] for incompressible and inviscid flow can actually be directly applied to the most general compressible and even transonic regimes. ...
... At M ∞ 0 (incompressible case), Eqs. (15)(16)(17) have been used with F rev given by Eq. (12) and F irr by Eq. (13). At M ∞ 0.3 (subsonic case), the aerodynamic force breakdown has been provided by Eqs. ...
Prandtl introduced the best wing system or Box Wing a century ago and showed its exceptional lift-induced drag performance with respect to wing systems having the same wingspan and lift (Prandtl, L., “Induced Drag of Multiplanes,” NACA TN-182, 1924.). In this work, and for the first time, their superior induced drag properties are verified in compressible and transonic regimes. The aerodynamic forces are obtained by analyzing computational fluid dynamics data, and the drag is subdivided in induced, viscous, and wave contributions. This decomposition is provided by a recently introduced aerodynamic force breakdown technique based on the vortex-force theory and allows an unambiguous definition of the lift-induced drag. The methodology is applicable to incompressible, compressible, and transonic flows. This paper will address whether the Best Wing system provides interesting induced drag performance also in transonic viscous flow.
... The current literature features many box wing aerodynamic studies using simulation, analytical and parametric methods [7][8][9][10]. Research has shed light on the aerodynamic benefits of the box-wing design. ...
Highly non-planar aircraft configurations promise vast improvements concerning aircraft efficiency, but their flight mechanical properties are currently not well understood. Using reference wind tunnel data and RANS CFD (STAR-CCM+) results, a vortex lattice solver (VSPAERO) and a surface vorticity flow solver (FlightStream) are being evaluated concerning their ability to model joined and box wing longitudinal aerodynamic characteristics. It is shown that FlightStream is able to provide results of CFD-like quality, as long as flow separation effects do not become prominent. VSPAERO delivers good lift and pitching moment results, but lacks in drag modelling. STAR-CCM+’s solutions come very close to wind tunnel results.
