Chinese Journal of Aeronautics最新文献

The Ti17(α + β)-Ti17(β) dual alloy-dual property blisk produced using Linear Friction Welding (LFW) is considered as high-performance component in advanced aeroengine. However, up to now, microstructure evolution and relationship between microstructure and micro mechanical properties of LFWed Ti17(α + β)/Ti17(β) dissimilar joint have not been thoroughly revealed. In this work, complex analyses of the phase transformation mechanisms of the joint are conducted, and phase transformations in individual zones are correlated to their microhardness and nanohardness. Results reveal that α dissolution occurs under high temperatures encountered during LFW, which reduces microhardness of the joint to that of Ti17(α + β) and Ti17(β). In Thermo-Mechanically Affected Zone of Ti17(α + β) (TMAZ-(α + β)) side joint, a large number of nanocrystalline α phases form with different orientations. This microstructure strengthens significantly by fine grains which balances partial softening effect of α dissolution, and increases nanohardness of α phase and microhardness of TMAZ-(α + β). Superlattice metastable β phase precipitates from metastable β in Weld Zone (WZ) during quick cooling following welding, because of short-range diffusion migration of solute atoms, especially β stabilizing elements Mo and Cr. The precipitation of the superlattice metastable β phase results in precipitation strengthening, which in turn increases nanohardness of metastable β and microhardness in WZ.

Atmosphere-Breathing Electric Propulsion (ABEP) can compensate for lost momentum of spacecraft operating in Very Low Earth Orbit (VLEO) which has been widely concerned due to its excellent commercial potential. It is a key technology to improve the capture efficiency of intakes, which collect and compress the atmosphere for ABEP. In this paper, the mechanism of the capture section affecting capture efficiency is investigated by Test Particle Monte Carlo (TPMC) simulations with 3D intake models. The inner surface smoothness and average collision number are determined to be key factors affecting capture efficiency, and a negative effect growth model is accordingly established. When the inner surface smoothness is less than 0.2, the highest capture efficiency and its corresponding average collision number interval are independent of the capture section’s geometry and its mesh size. When the inner surface smoothness is higher than 0.2, the capture efficiency will decrease by installing any capture section. Based on the present results, the manufacturing process and material selection are suggested to be prioritized during the intake geometry design in engineering projects. Then, the highest capture efficiency can be achieved by adjusting the length and mesh size of the capture section.

The in-cylinder gas exchange process is crucial to the power performance of two-stroke aircraft piston engines, which is easily influenced by complex factors such as high-altitude performance variation and in-cylinder flow characteristics. This paper reviews the development history and characteristics of gas exchange types, as well as the current state of theory and the validation methods of gas exchange technology, while also discusses the trends of cutting-edge technologies in the field. This paper provides a theoretical foundation for the optimization and engineering design of gas exchange systems and, more importantly, points out that the innovation of gas exchange types, the modification of theoretical models, and the technology of variable airflow organization are the key future research directions in this field.

The problem of removing unused liquid propellant residues from the tanks of spent spacecraft and orbital stages of Launch Vehicles (LV) leads to their explosion and the formation of space debris in orbits. To provide a solution to this problem, a method for removing liquid propellant residues from the LV tanks after the mission completion is proposed. The method is based on the gasification of liquid propellant residues in the tanks under acoustic-vacuum exposure and the discharge of the gasification products into the surrounding outer space. Experimental investigations were carried out on a Ground-based Experimental Installation (GEI) to determine the coefficient of heat transfer from the surface of an acoustic radiator to a liquid. The obtained coefficient was then used to calculate the energy costs for the gasification of kerosene. Numerical estimates are given on the example of the tank with kerosene residues from a spent second stage of the LV “Soyuz-2.1 v”. The optimal discharge rate at which kerosene does not freeze is 0.14 m³/s. Moreover, the acoustic exposure leads to an increase in the mass of evaporated kerosene over a given time by 96.1%, and the energy costs are 1756.7 kJ (approximately 50% of the remaining electrical energy).

The 8 mm-thick 2195 Al-Li alloy joints were achieved by Friction Stir Welding (FSW). The microstructural evolution, temperature-dependent mechanical properties, and fracture properties were studied. The T₁, δ′/β′ and θ′ precipitates were observed in the Base Metal (BM) and the Heat Affected Zone (HAZ). Most of the precipitates, except for re-precipitated δ′/β′ phases, were dissolved in the Nugget Zone (NZ). The tensile specimens that failed at cryogenic temperatures (–196 °C) had the maximum Ultimate Tensile Strength (UTS), and the fracture surface showed the inter-granular fracture characteristics. Compared to those at room temperature (25 °C), the decreasing tensile properties at high temperature (180 °C) were related to microstructure and strain hardening effects. The NZ presented the optimal fracture toughness, and the Crack Tip Opening Displacement (CTOD) was mutually dominated by microhardness and grain size. Analysis on Fatigue Crack Growth (FCG) rates indicates that the Thermal-Mechanically Affected Zone (TMAZ) exhibited the most superior fatigue resistance performance at stress intensity range below 17 MPa·m^1/2 due to compressive residual stress and the crack closure effect. The fatigue fracture surfaces reveal that the crack propagation zone was characterized by the striations and secondary cracks. Also, inter-granular fracture behavior was responsible for the fastest FCG rates in the NZ.

The rapid development of the anti-missile weapon technology brings new challenges to the cooperative penetration strategy solution and the guidance law design for Hypersonic Vehicles (HVs). This paper studies the coordinated game penetration guidance problem for multiple hypersonic vehicles faced with space threat areas. A scheme for seeking cooperative game penetration guidance strategy under safety critical control framework is presented. In this scheme, a multi-HV cooperative game model is proposed in a minimum optimization form which can simplify the solving process and accelerate the computing speed. Then, a second-order control barrier function is developed to transform the implicit nonlinear constraints of the proposed model into linear ones. In order to obtain better performance of guidance strategy, a composite guidance law under the safety critical control framework is presented to allocate guidance strategies appropriately in the whole process. It is shown that the proposed scheme can guarantee successful penetration while avoiding threat areas. Finally, a comparative simulation with a two-on-three game is conducted to verify the effectiveness of the proposed method.

Multi-modal image matching is crucial in aerospace applications because it can fully exploit the complementary and valuable information contained in the amount and diversity of remote sensing images. However, it remains a challenging task due to significant non-linear radiometric, geometric differences, and noise across different sensors. To improve the performance of heterologous image matching, this paper proposes a normalized self-similarity region descriptor to extract consistent structural information. We first construct the pointwise self-similarity region descriptor based on the Euclidean distance between adjacent image blocks to reflect the structural properties of multi-modal images. Then, a linear normalization approach is used to form Modality Independent Region Descriptor (MIRD), which can effectively distinguish structural features such as points, lines, corners, and flat between multi-modal images. To further improve the matching accuracy, the included angle cosine similarity metric is adopted to exploit the directional vector information of multi-dimensional feature descriptors. The experimental results show that the proposed MIRD has better matching accuracy and robustness for various multi-modal image matching than the state-of-the-art methods. MIRD can effectively extract consistent geometric structure features and suppress the influence of SAR speckle noise using non-local neighboring image blocks operation, effectively applied to various multi-modal image matching.

This paper is devoted to application of the Reduced-Order Model (ROM) based on Volterra series to prediction of lift and drag forces due to airfoil periodic translation in transonic flow region. When there is large amplitude oscillation of the relative Mach number, as appeared in helicopter rotor movement in forward flight, the conventional Volterra ROM is found to be unsatisfactory. To cover such applications, a matched Volterra ROM, inspired from previous multistep nonlinear indicial response method based on Duhamel integration, is thus considered, in which the step motions are defined inside a number of equal intervals with both positive and negative step motions to match the airfoil forward and backward movement, and the kernel functions are constructed independently at each interval. It shows that, at least for the translation movement considered, this matched Volterra ROM greatly improves the accuracy of prediction. Moreover, the matched Volterra ROM, with the total number of step motions and thus the computational cost close to those of the conventional Volterra ROM method, has the additional advantage that the same set of kernels can match various translation motions with different starting conditions so the kernels can be predesigned without knowing the specific motion of airfoil.

This article focuses on asymptotic precision motion control for electro-hydraulic axis systems under unknown time-variant parameters, mismatched and matched disturbances. Different from the traditional adaptive results that are applied to dispose of unknown constant parameters only, the unique feature is that an adaptive-gain nonlinear term is introduced into the control design to handle unknown time-variant parameters. Concurrently both mismatched and matched disturbances existing in electro-hydraulic axis systems can also be addressed in this way. With skillful integration of the backstepping technique and the adaptive control, a synthesized controller framework is successfully developed for electro-hydraulic axis systems, in which the coupled interaction between parameter estimation and disturbance estimation is avoided. Accordingly, this designed controller has the capacity of low-computation costs and simpler parameter tuning when compared to the other ones that integrate the adaptive control and observer/estimator-based technique to dividually handle parameter uncertainties and disturbances. Also, a nonlinear filter is designed to eliminate the “explosion of complexity” issue existing in the classical back-stepping technique. The stability analysis uncovers that all the closed-loop signals are bounded and the asymptotic tracking performance is also assured. Finally, contrastive experiment results validate the superiority of the developed method as well.

The wheel brake system of an aircraft is the key to ensure its safe landing and rejected takeoff. A wheel’s slip state is determined by the brake torque and ground adhesion torque, both of which have a large degree of uncertainty. It is this nature that brings upon the challenge of obtaining high deceleration rate for aircraft brake control. To overcome the disturbances caused by the above uncertainties, a braking control law is designed, which consists of two parts: runway surface recognition and wheel’s slip state tracking. In runway surface recognition, the identification rules balancing safety and braking efficiency are defined, and the actual identification process is realized through recursive least square method with forgetting factors. In slip state tracking, the LuGre model with parameter adaptation and a brake torque compensation method based on RBF neural network are proposed, and their convergence are proven. The effectiveness of our control law is verified through simulation and ground experiment. Especially in the experiments on the ground inertial test bench, compared to the improved pressure-biased-modulation (PBM) anti-skid algorithm, fewer wheel slips occur, and the average deceleration rate is increased by 5.78%, which makes it a control strategy with potential for engineering applications.