Progress in Aerospace Sciences最新文献

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.

This article presents a review of historical and recent developments in the understanding of equilibrium and non-equilibrium turbulent boundary layers at incompressible high-Reynolds number conditions. The most fundamental equations and concepts are first introduced to provide a basis and context for the material reviewed. The review focusses on findings concerning the mean flow and turbulence stress fields, as well as on major elements of the instantaneous structure. Zero pressure gradient smooth wall and rough wall boundary layers are described, forming the basis of following material on equilibrium boundary layers formed in favorable and adverse pressure gradients. Non-equilibrium two dimensional flows formed in pressure gradient, with and without roughness, and as a result of step changes in roughness are covered. A detailed discussion of the physics and mathematics unique to the development of boundary layers in skewed, three-dimensional flows over smooth walls concludes the review.

The network of interactions among fluid elements and coherent structures gives rise to the incredibly rich dynamics of vortical flows. These interactions can be described with the use of mathematical tools from the emerging field of network science, which leverages graph theory, dynamical systems theory, data science, and control theory. The blending of network science and fluid mechanics facilitates the extraction of the key interactions and communities in terms of vortical elements, modal structures, and particle trajectories. Phase-space techniques and time-delay embedding enable a network-based analysis of time-series measurements in terms of visibility, recurrence, and cluster transitions. Equipped with the knowledge of interactions and communities, the network-theoretic approach enables the analysis, modeling, and control of fluid flows, with a particular emphasis on interactive dynamics. In this article, we provide a brief introduction to network science and an overview of the progress on network-based strategies to study the complex dynamics of fluid flows. Case studies are surveyed to highlight the utility of network-based techniques to tackle a range of problems from fluid mechanics. Towards the end of the paper, we offer an outlook on network-inspired approaches.

About a century ago, two different rotor models were proposed by Joukowsky (1912–1918) and Betz (1919). Both models were based on assumptions regarding the vortex structures of the wake and its induction on the rotor plane. However, due to complications of formulating the wake behavior into actual guidelines for the aerodynamic design of the rotor geometry, the models have until now not been used to design actual industrial wind turbine rotors. In this article, we propose a technique to solve analytically the induction problem of the two models, which enables the design of wind turbine rotors. We briefly present the theory behind the two rotor models, and show how this theory can be exploited to make actual designs of rotor planforms, i.e. chord- and twist-distributions. The designs are for three-bladed rotors optimized for different tip speed ratios and analyzed by comparing their performance to results using blade-element/momentum technique and lifting line theory.

Given the few unsuccessful space missions in the past few decades, designing a fault-tolerant spacecraft’s attitude control has piqued the scientific and academic community’s attention. In recent years, fault-tolerant control (FTC) emerged as a prominent control strategy to ensure the reliability and safety of modern systems. This paper critically assesses various theoretical and practical design approaches to achieve the desired level of fault-tolerance for the spacecraft’s attitude control. First, a run-through on the conventional FTC methodology for spacecraft’s attitude control is briefly presented, highlighting the shortcomings. Then, the need for an autonomous FTC for present and future space missions is established. More critically, a detailed review of the latest developments in spacecraft’s fault-tolerant attitude control is discussed from two perspectives: controller-basis design techniques and various controller performance characteristics. Finally, several key challenges and open research areas in designing a practical and reliable spacecraft’s fault-tolerant attitude control and the window for future research prospects are discussed.

An aerospace structure is built from the assembly of structural sub-components involving joining technologies such as welding, mechanical fastening or adhesive bonding.

The function of joints is to ensure load transfer between the structural sub-components. The integrity of the structure directly depends on strength of these joints. In order to design these critical structural areas, load transfer between structural sub-components must be assessed. The objective of this review paper is to present approaches for the simplified modelling and associated resolution schemes of single-lap adhesively bonded and hybrid (bolted/bonded) joints to predict load transfer. We show that the scope of available closed-form solutions is restricted, such that the use of semi-analytical schemes is suitable. Macro-element modelling is then presented. This technique allows the assessment of load transfer and associated stresses, especially in the adhesive layer regarded as a cohesive zone, while enabling the enrichment of the model, making it more representative of the physical reality.

Turbofan engines are one of the most popular propulsion systems used in commercial aircraft due to their high thrust and good fuel efficiency. To reduce noise generated from turbofan engines-powered aircraft, a number of control approaches have been developed. The dominant noise sources include the fan and the high-speed ‘hot’ and ‘cold’ jet. In engineering applications, the noise control approaches include: 1) active control, 2) geometric shape optimization, and 3) passive control (including acoustic boundary control). Because they are considered the most reliable and effective noise reduction methods, the geometric shape optimization and passive control are preferable by the engine manufacturers. In this work, we briefly overview the noise reduction technologies that have great potential to be applied or implemented on turbofan engines. The research and development progress made on the active control, passive control, and geometric shape optimization are reviewed and discussed, aiming to provide an useful guidance on next-generation low-noise turbofan engines. The fundamental noise damping mechanisms of thermos-viscous and vortex shedding are finally overviewed via cases studies.

Growing interest in unconventional aircraft designs coupled with miniaturization of electronics and advancements in manufacturing techniques have revived the interest in the use of Sub-scale Flight Testing (SFT) to study the flight behaviour of full-scale aircraft in the early stages of design process by means of free-flying sub-scale models. SFT is particularly useful in the study of unconventional aircraft configurations as their behaviour cannot be reliably predicted based on legacy aircraft designs. In this paper, we survey the evolution of various design approaches (from 1848 to 2021) used to ensure similitude between a sub-scale model and its full-scale counterpart, which is an essential requirement to effectively perform SFT. Next, we present an exhaustive list of existing sub-scale models used in SFT and analyse the key trends in their design approaches, test-objectives, and applications. From this review, we conclude that the state-of-the-art sub-scale model design methods available in literature have not been used extensively in practice. Furthermore, we argue that one sub-scale model is not sufficient to predict the complete flight behaviour of a full-scale aircraft, but a catalog of tailored sub-scale models is needed to predict full-scale behaviour. An introduction to the development of such a catalog is presented in this paper, but the development of a formal methodology remains an open challenge. Establishing an approach to develop and use a SFT catalog of models to predict full-scale aircraft behaviour will help engineers enhance confidence on their designs and make SFT a viable and attractive testing method in the early stages of design.

Computational fluid dynamics (CFD) methods used for the numerical solution of the Euler and Navier–Stokes equations have been sufficiently matured and enable to perform high fidelity simulations in fluid dynamics research and engineering applications. In this review, some low-order (second order or lower) accurate space–time-domain discretization schemes that are still widely in use are reviewed first, in order to show the benefits of high order numerical schemes and the techniques for stability and error analysis. Then, popular high order spatial discretization schemes are discussed to highlight the benefits and also the challenges they impose on high order implicit time advancement. After these, we focus on the major aspects of implicit time advancement combining the Runge–Kutta methods and high order spatial discretizations that have been proven efficient to resolve unsteady flows. In addition to the construction of high order implicit Runge–Kutta schemes, more recent development concerning enhanced nonlinear stability and low-dispersion low-dissipation errors is discussed in detail for multi-physical flow phenomena. Efficient solution techniques for implicit parallel solutions on advanced high-performance computers are reviewed, such as the traditional LU-SGS and ADI methods based on the approximate factorization, the Newton iterative method with subsidiary iterations, etc. As another challenging issue, enforcement of implicit boundary conditions is also elaborated, and we focus especially on the recent developments and the benefits they offer regarding computational efficiency and accuracy.

Inlet flow distortion is expected to play a major role in future aircraft architectures where complex air induction systems are required to couple the engine with the airframe. The highly unsteady distortions generated by such intake systems can be detrimental to engine performance and were previously linked with loss of engine stability and potentially catastrophic consequences. During aircraft design, inlet flow distortion is typically evaluated at the aerodynamic interface plane, which is defined as a cross-flow plane located at a specific upstream distance from the engine fan. Industrial testing currently puts more emphasis on steady state distortions despite the fact that, historically, unsteady distortions were acknowledged as equally important. This was partially due to the limitations of intrusive measurement methods to deliver unsteady data of high spatial resolution in combination with their high cost and complexity. However, as the development of aircraft with fuselage-integrated engine concepts progresses, the combination of different types of flow distortions is expected to have a strong impact on the engine’s stability margin. Therefore, the need for novel measurement methods able to meet the anticipated demand for more comprehensive flow information is now more critical than ever. In reviewing the capabilities of various non-intrusive methods for inlet distortion measurements, Filtered Rayleigh Scattering (FRS) is found to have the highest potential for synchronously characterising multiple types of inlet flow distortions, since the method has the proven ability to simultaneously measure velocity, static pressure and temperature fields in challenging experimental environments. The attributes of the FRS method are further analysed aiming to deliver a roadmap for its application on ground-based and in-flight measurement environments.