Progress in Aerospace Sciences最新文献

The utilization of hybrid electric propulsion concept in aviation offers a viable solution to address the limitations posed by the relatively low energy density of batteries in fully electric aviation. These hybrid systems enable the aircraft to achieve a significant range while simultaneously minimizing carbon emissions. While the individual components of a Hybrid Electric Propulsion (HEP) system, such as electric motors and batteries, are designed with high efficiency, their integration presents a significant challenge in the realm of thermal management. Designing an efficient system for managing the substantial waste heat generated by heat sources and effectively transferring it to heat sinks during various flight phases is a complex task. This challenge becomes even more critical as the design must adhere to system weight limits and prioritize aviation safety considerations. In this review article, we performed a systematic review of the challenges related to the key elements in a thermal management system. These elements encompass every component or subsystem that contributes to the thermal management of a generic hybrid-electric propulsion system. This includes electric motors and generators, batteries, heat exchangers, power transmission systems, power distribution systems, storages, fuel cells, cooling fluids and pipes, control system, pumps and fans. Following the identification of the challenges, the paper provides a comprehensive summary of the existing solutions that have been offered and pursued by the community to address the challenges. Furthermore, the paper also discusses emerging technologies related to each element, highlighting their potential in overcoming these challenges.

A hypersonic inlet/isolator acts as the “compressor” for scramjet engines through a series of shocks, which induces complex internal flows. This paper comprehensively reviews the recent research achievements, focusing on the shock-dominated internal flow of an inlet/isolator. Considering the specific geometrical feature of the hypersonic inlet, the shock wave/boundary layer interactions (SWBLIs) are characterized by multiple successive shocks. Three types of couplings have been observed between adjacent interaction regions. Moreover, shock and expansion waves, which are induced by the SWBLIs and named “background wave”, are reflected in an isolator, forming a background wave/shock train interaction flow. The shock train behavior significantly differs from that in direct-connect facilities under uniform incoming flow conditions, and energy-level-transition-like phenomenon is observed when the shock train intersects with the background wave. Four types of quasi-steady background wave/shock train interactions have been reported, and three types of dynamic transitions have been observed when the shock train passes across the reflection point of the background shock. After the shock train is expelled from the internal duct, the inlet/isolator falls into unstart, and the unsteady shock-dominated flow with violent low-frequency shock oscillation occurs. A typical unstart period contains several stages, including the motion of the shock train in the isolator, large-scale separation in the inlet, and shock oscillation at the external part of the inlet. The flow mechanics of the hypersonic inlet/isolator unstart differs from that of a supersonic inlet. An unstart loop for a hypersonic inlet/isolator has been proposed, including convection wave, shock train, and acoustic wave. Once the induced factor of the unstart is removed, the unstarted shock retreats and the inlet experiences restart with the rebuilding of the supersonic flow. The restart process is highly dependent on the initial flow state and the historical effect. An instantaneous buzz arises before the unstarted shock retreats into the internal duct. Finally, the related passive (e.g., micro-vortex generator, bump, boundary layer bleed and self-circulation secondary flow control method) and active flow control methods (e.g., air jet vortex generator, plasma jet flow control, and solid-particle injection) for weakening the unfavorable impact of these shock-dominated flows are reviewed. Furthermore, the control mechanics and control effects of these flow control methods are analyzed.

A review of the literature on the methods for activation of the combustion of metallic fuels, mainly boron-containing ones, as the promising components of composite propellants for ramjets is presented. Some methods and ideas were checked experimentally using a laboratory approach developed for comparing the metallic fuels (MF) of different origin. The approach implies the determination of the set of propellant combustion parameters, such as: burning rate, mass of condensed combustion products (CCP), MF combustion completeness, and heat release efficiency (HRE). The CCP particles are firstly quenched in an inert gas, and then sampled and subjected to particle size and chemical analyses. Seventeen propellants, containing different fuels, were studied at pressures of 1.2 and 2.5 МPа. The formulation factors that affect the burning rate and HRE were revealed. Recommendations on future directions of the studies on promising propellant formulations are given.

Standing oblique detonation is a unique pressure-gain combustion phenomenon for hypersonic ramjet propulsion, and its research has been related with supersonic combustion in scramjet engines since its births, for example, absent treatment in its early stage and re-consideration in recent decades. Standing oblique detonations and supersonic combustion share the same features of supersonic chemically-reacting flows, and can be considered as different flow development stages. Combustion instability in a chemically-reacting flow is reviewed first to identify its fundamental mechanisms, and the upstream-propagating shock wave is identified as one of intrinsic characteristics and taken as the key problem for developing hypersonic ramjet propulsion. Critical conditions for the standing oblique detonation are summarized as a theoretical base for standing oblique detonation ramjet engines. Three key parameters are included, that is, the maximum heat that can drive local flow states from supersonic to sonic after combustion, the critical inflow Mach number of combustors, at which supersonic combustion becomes stable, and the critical wedge angle at which a standing oblique detonation can be initiated. The evolution of the standing oblique detonation is reviewed by placing emphasis on its complex wave structure that was found to develop via three stages, that is, shock-induced initiation, the decaying stage and the fully-developed stage. Finally, progress in experimental research is reviewed with detailed discussions on stabilization of the standing oblique detonation, experimental methods and development of adequate test facilities. In conclusion, the stable operation of hypersonic ramjet propulsion is a critical issue to approach its engineering application, and the standing oblique detonation ramjet engine is recommended as a promising candidate, deserving more attention in the future.

A review of research progress in the design of the exhaust system for the scramjet and turbine based combined cycle (TBCC) engine is presented. Firstly, the technical challenges encountered in designing the exhaust system for a hypersonic propulsion system are highlighted and discussed, and the performance parameter definition as well as the theoretical thrust prediction for the exhaust system is introduced. The review of scramjet nozzle focuses on three aspects: 1) the design method of the single expansion ramp nozzle (SERN) for the integration of the airframe with the propulsion system, in which the design method developments of the two-dimensional (2D) SERN, SERN with lateral expansion and three-dimensional (3D) SERN with shape transition are all summarized; 2) the unique flow phenomena of the scramjet nozzle, including the nonuniform inflow and chemical nonequilibrium flow in SERN; 3) the coupling and interaction of the internal flow with the external freestream. Besides, the design and flow researches of the TBCC exhaust system is also reviewed for three parts: 1) variable geometry design for wide flight range, in which both a 2D and 3D exhaust system are described; 2) the overexpanded flow separation mechanism and its control at low flight Mach number; 3) mode transition from low-speed flowpath (LSF) to high-speed flowpath (HSF) for over-under exhaust system. Through the above summary and analysis, the current status, bottlenecks, and development trend of the exhaust system for an airbreathing hypersonic propulsion system can be further clarified.

The vast majority of shock wave–boundary-layer interactions in practical applications like supersonic aircraft intakes are three dimensional in nature. The complex behaviour of such interactions can generally be understood by combining the flow physics of a limited number of canonical cases. The physical understanding of these flow fields developed by numerous investigators over the last half century is reviewed, focusing predominantly on steady aspects of turbulent, uncontrolled interactions in the transonic and supersonic regimes, i.e. for Mach number less than 5. Key physical features of the flow fields and recent developments are described for swept compression corners, various fin interactions, semi-cones, vertical cylinder-induced interactions, swept oblique shock reflections and flared cylinders. In addition to the canonical geometries, a different type of three dimensionality concerning sidewall effects in duct flows, like intakes or propulsion systems, is also reviewed. The underlying mechanisms, centred on pressure waves propagating from the corner regions, are introduced and the implications for separation unsteadiness and flow control are discussed.

From the perspective of aeronautical engineers, this paper gives a systematical summary of the technical aspects of bird flight that should be considered in the analysis and design of flapping unmanned and micro air vehicles (UAVs and MAVs). The relevant aspects include the scaling laws, avian wing geometry, avian wing kinematics, aerodynamics models, computations, and special topics. Instead of extensively and uniformly reviewing a wide range of materials studied by avian biologists, we focus on the analytical and semi-analytical models and quantitative data as the useful guidelines for the design of flapping UAVs and MAVs.

This comprehensive study delves into the significance of asteroid research and proposes a systematic classification consisting of seven distinct categories. Initially, a concise definition is presented to differentiate between asteroids, meteorites, and comets, accompanied by a brief exploration of their unique characteristics. Recognizing the valuable scientific insights that these celestial bodies hold, the reasons for studying asteroids are categorized as follows: 1) Life's origin, 2) The Moon's origin, 3) The origin of water on Earth, 4) Vast reservoirs of valuable resources, 5) Colonization, 6) Threats, and 7) Advancing our understanding of physics. This paper meticulously reviews these seven reasons and subsequently delves into the achievements of past missions to low-gravity bodies, including Pioneer 10, Galileo, Clementine, NEAR Shoemaker, Deep Space 1, Cassini–Huygens, Stardust, Hayabusa, New Horizons, Rosetta, Dawn, Change 2, Hayabusa2, Lucy, Dart, and OSIRIS-REx. Additionally, future missions are introduced, while the challenges associated with flybys, mining operations, and asteroid landings are thoroughly examined.

Hierarchical structures provide a means to systematically deconstruct an engineering system of arbitrary complexity into its subsystems, components, and physical processes. Model validation hierarchies can aid in understanding the coupling and interaction of subsystems and components, as well as improve the understanding of how simulation models are used to design and optimize the engineering system of interest. The upper tiers of the hierarchy address systems and subsystems architecture decompositions, while the lower tiers address physical processes that are both coupled and uncoupled. Recent work connects these two general sections of the hierarchy through a transition tier, which blends the focus of system functionality and physics modeling activities. This work also includes a general methodology for how a model validation hierarchy can be constructed for any type of engineering system in any operating environment, e.g., land, air, sea, or space. We review previous work on the construction and use of model validation hierarchies in not only the field of aerospace systems, but also from commercial nuclear power plant systems. Then an example of a detailed model validation hierarchy is constructed and discussed for a surface-to-air missile defense system with an emphasis on the missile subsystems.