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.

Thrust estimation is a significant part of aeroengine thrust control systems. The traditional estimation methods are either low in accuracy or large in computation. To further improve the estimation effect, a thrust estimator based on Multi-layer Residual Temporal Convolutional Network (M-RTCN) is proposed. To solve the problem of dead Rectified Linear Unit (ReLU), the proposed method uses the Gaussian Error Linear Unit (GELU) activation function instead of ReLU in residual block. Then the overall architecture of the multi-layer convolutional network is adjusted by using residual connections, so that the network thrust estimation effect and memory consumption are further improved. Moreover, the comparison with seven other methods shows that the proposed method has the advantages of higher estimation accuracy and faster convergence speed. Furthermore, six neural network models are deployed in the embedded controller of the micro-turbojet engine. The Hardware-in-the-Loop (HIL) testing results demonstrate the superiority of M-RTCN in terms of estimation accuracy, memory occupation and running time. Finally, an ignition verification is conducted to confirm the expected thrust estimation and real-time performance.

An improved Reduced-Order Model (ROM) is proposed based on a flow-solution preprocessing operation and a fast sampling strategy to efficiently and accurately predict ionized hypersonic flows. This ROM is generated in low-dimensional space by performing the Proper Orthogonal Decomposition (POD) on snapshots and is coupled with the Radial Basis Function (RBF) to achieve fast prediction speed. However, due to the disparate scales in the ionized flow field, the conventional ROM usually generates spurious negative errors. Here, this issue is addressed by performing flow-solution preprocessing in logarithmic space to improve the conventional ROM. Then, extra orthogonal polynomials are introduced in the RBF interpolation to achieve additional improvement of the prediction accuracy. In addition, to construct high-efficiency snapshots, a trajectory-constrained adaptive sampling strategy based on convex hull optimization is developed. To evaluate the performance of the proposed fast prediction method, two hypersonic vehicles with classic configurations, i.e. a wave-rider and a reentry capsule, are used to validate the proposed method. Both two cases show that the proposed fast prediction method has high accuracy near the vehicle surface and the free-stream region where the flow field is smooth. Compared with the conventional ROM prediction, the prediction results are significantly improved by the proposed method around the discontinuities, e.g. the shock wave and the ionized layer. As a result, the proposed fast prediction method reduces the error of the conventional ROM by at least 45%, with a speedup of approximately 2.0 × 10⁵ compared to the Computational Fluid Dynamic (CFD) simulations. These test cases demonstrate that the method developed here is efficient and accurate for predicting ionized hypersonic flows.

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 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.

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.

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.

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.

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.