Chinese Journal of Aeronautics最新文献

Variable camber wing technology is one of the important development trends of green aviation at present. Through smooth, seamless, continuous and adaptive change of wing camber, the aerodynamic performance is improved in achieving increase in lift and reduction in resistance and noise. Based on the aerodynamic validation model CAE-AVM, Chinese Aeronautical Establishment (CAE) has carried out the design and validation of a variable camber wing, proposed an aerodynamic deformation matrix for the leading and trailing edges of aircraft wings in take-off, landing and cruise conditions. Various structures and driving schemes are compared, and several key technology problems of leading and trailing edge deformation are solved. A full-size leading edge wind tunnel test piece with a span of 2.7 m and a trailing edge ground function test piece are developed. The deformation and shape maintenance capabilities of the leading edge is verified under real wind load conditions, and the load bearing and deformation capabilities of the trailing edge is verified under simulated follow-on load. The results indicate that the leading and trailing edges of the variable camber wing can achieve the required deformation angle and have a certain load-bearing capacity. Our study can provide some insights into the application of variable camber wing technology for civil aircraft.

The metal cutting process is accompanied by complex stress field, strain field, temperature field. The comprehensive effects of process parameters on chip morphology, cutting force, tool wear and residual stress are complex and inter-connected. Finite element method (FEM) is considered as an effective method to predict process variables and reveal microscopic physical phenomena in the cutting process. Therefore, the finite element (FE) simulation is used to research the conventional and micro scale cutting process, and the differences in the establishment of process variable FE simulation models are distinguished, thereby improving the accuracy of FE simulation. The reliability and effectiveness of FE simulation model largely depend on the accuracy of the simulation method, constitutive model, friction model, damage model in describing mesh element, the dynamic mechanical behavior of materials, the tool-chip-workpiece contact process and the chip formation mechanism. In this paper, the FE models of conventional and micro process variables are comprehensively and up-to-date reviewed for different materials and machining methods. The purpose is to establish a FE model that is more in line with the real cutting conditions, and to provide the possibility for optimizing the cutting process variables. The development direction of FE simulation of metal cutting process is discussed, which provides guidance for future cutting process modeling.

With the great development of Multi-Target Tracking (MTT) technologies, many MTT algorithms have been proposed with their own advantages and disadvantages. Due to the fact that requirements to MTT algorithms vary from the application scenarios, performance evaluation is significant to select an appropriate MTT algorithm for the specific application scenario. In this paper, we propose a performance evaluation method on the sets of trajectories with temporal dimension specifics to compare the estimated trajectories with the true trajectories. The proposed method evaluates the estimate results of an MTT algorithm in terms of tracking accuracy, continuity and clarity. Furthermore, its computation is based on a multi-dimensional assignment problem, which is formulated as a computable form using linear programming. To enhance the influence of recent estimated states of the trajectories in the evaluation, an attention function is used to reweight the trajectory errors at different time steps. Finally, simulation results show that the proposed performance evaluation method is able to evaluate many aspects of the MTT algorithms. These evaluations are worthy for selecting suitable MTT algorithms in different application scenarios.

Dry friction damping structures are widely-used in aero-engines to mitigate vibration. The nonlinear nature of friction and the two-dimensional in-plane motion on the contact interface bring challenges to accurately and efficiently predict the forced response of frictionally damped structures. The state-of-the-art Multi-Harmonic Balance Method (MHBM) on quasi-3D contact model in engineering cannot precisely capture the kinematics on the friction interface although the efficiency is high. The full-3D contact model can describe the constitutive relationship of the interface in a more accurate manner; however, the efficiency and convergence are not guaranteed for large-scale models. In this paper, a semi-analytical MHBM on full-3D contact model is proposed. The original Trajectory Tracking Method (TTM) for evaluating the contact force is reformulated to make the calculation more concise and the derivation of the Analytical Jacobian Matrix (AJM) feasible. Based on the chain rule of derivation, the AJM which is the core to upgrade the performance is deduced. Through a shrouded blade finite element model, the accuracy and efficiency of the proposed method are compared with both the MHBM on full-3D contact model with numerical Jacobian matrix and the MHBM on quasi-3D contact model with AJM. The results show that the AJM improves significantly the efficiency of the MHBM on full-3D contact model. The time cost of the proposed method is in the same order of magnitude as that of the MHBM on quasi-3D contact model. We also confirm that the full-3D contact model is necessary for the dynamic analyses of shrouded blades. If one uses the quasi-3D model, the estimation relative error of damping can even reach 31.8% in some cases. In addition, the AJM also brings benefits for stability analysis. It is highly recommended that engineers use the MHBM on full-3D contact model for the dynamic analysis and design of shrouded blades.

Relative positioning is recognized as an important issue for vehicles in urban environments. Multi-vehicle Cooperative Positioning (CP) techniques which fuse the Global Navigation Satellite System (GNSS) and inter-vehicle ranging have attracted attention in improving the performance of baseline estimation between vehicles. However, current CP methods estimate the baselines separately and ignore the interactions among the positioning information of different baselines. These interactions are called ‘information coupling’. In this work, we propose a new multi-vehicle precise CP framework using the coupled information in the network based on the Carrier Differential GNSS (CDGNSS) and inter-vehicle ranging. We demonstrate the benefit of the coupled information by deriving the Cramer-Rao Lower Bound (CRLB) of the float estimation in CP. To fully use this coupled information, we propose a Whole-Net CP (WN-CP) method which consists of the Whole-Net Extended Kalman Filter (WN-EKF) as the float estimation filter, and the Partial Baseline Fixing (PBF) as the ambiguity resolution part. The WN-EKF fuses the measurements of all baselines simultaneously to improve the performance of float estimation, and the PBF strategy fixes the ambiguities of the one baseline to be estimated, instead of full ambiguity resolution, to reduce the computation load of ambiguity resolution. Field tests involving four vehicles were conducted in urban environments. The results show that the proposed WN-CP method can achieve better performance and meanwhile maintain a low computation load compared to the existing methods.

The multi-body flexible morphing airfoil can improve the aerodynamic characteristics based on different flight missions continuously. Recently researches have focused on the unsteady aerodynamic characteristics of flexible wings under passive actuation. However, the unsteady aerodynamic characteristics with the fluid–structure interaction effects in the multi-body active actuation process of morphing airfoil deserve further investigation. In this paper, a fluid–structure coupled simulation method for multi-body flexible morphing airfoil with active actuation subsystem was investigated, and the aerodynamic characteristics during deformation were compared with different skin flexibility, flow field environment, actuation mode and actuation time. The numerical results show that for the steady aerodynamic, the skin flexibility can improve the stability efficiency. In the unsteady process, the change trend of the transient lift coefficient and pitching moment are consistent with those of the active drive characteristics, while the instantaneous lift-drag ratio coefficient is greatly affected by the driving mode and can be improved by increasing the driving duration.

The design and application of morphing systems are ongoing issues compelling the aviation industry. The Clean Sky - program represents the most significant aeronautical research ever launched in Europe on advanced technologies for greening next-generation aircraft. The primary purpose of the program is to develop new concepts aimed at decreasing the effects of aviation on the environment, increasing reliability, and promoting eco-friendly mobility. These ambitions are pursued through research on enabling technologies fostering noise and gas emissions reduction, mainly by improving aircraft aerodynamic performances. Within the Clean Sky framework, a multimodal morphing flap device was designed based on tight industrial requirements and tailored for large civil aircraft applications. The flap is deployed in one unique setting, and its cross section is morphed differently in take-off and landing to get the necessary extra lift for the specific flight phase. Moreover, during the cruise, the tip of the flap is deflected for load control and induced drag reduction. Before manufacturing the first flap prototype, a high-speed (Ma = 0.3), large-scale test campaign (geometric scale factor 1:3) was deemed necessary to validate the performance improvements brought by this novel system at the aircraft level. On the other hand, the geometrical scaling of the flap prototype was considered impracticable due to the unscalability of the embedded mechanisms and actuators for shape transition. Therefore, a new architecture was conceived for the flap model to comply with the scaled dimensions requirements, withstand the relevant loads expected during the wind tunnel tests and emulate the shape transition capabilities of the true-scale flap. Simplified strategies were developed to effectively morph the model during wind tunnel tests while ensuring the robustness of each morphed configuration and maintaining adequate stiffness levels to prevent undesirable deviations from the intended aerodynamic shapes. Additionally, a simplified design was conceived for the flap-wing interface, allowing for quick adjustments of the flap setting and enabling load transmission paths like those arising between the full-scale flap and the wing. The design process followed for the definition of this challenging wind tunnel model has been addressed in this work, covering the definition of the conceptual layout, the numerical evaluation of the most severe loads expected during the test, and the verification of the structural layout by means of advanced finite element analyses.

Swept blades are widely utilized in transonic compressors/fans and provide high load, high through-flow, high efficiency, and adequate stall margin. However, there is limited quantitative research on the mechanism of the effect of swept blades on the flow field, resulting in a lack of direct quantitative guidance for the design and analysis of swept blades in fans/compressors. To better understand this mechanism, this study employs a reduced-dimensional force equilibrium method to analyze more than 1500 swept cascades data. Results verify that circumferential fluctuation terms are responsible for inducing radial migration in the inlet airflow field of the swept blade, resulting in variations in the incidence angle and consequently leading to changes in the characteristics of the swept blade. Thus, a combination of simple functions and machine learning is utilized to model the circumferential fluctuation terms and quantify the sweep mechanism. The prediction accuracy of the model is high, with coefficient of determination greater than 0.95 on the test set. When the model is applied in a meridional flow analysis program, the calculation accuracy of the program for the incidence angle is improved by 0.4° and 0.6° at the design and off-design conditions respectively, compensating for the program's original deficiencies. Meanwhile, the model can also provide quantitative guidance for the design of swept blades, thereby reducing the number of design iterations and improving design efficiency.

Small and micro unmanned aircraft are the focus of scientific interest due to their wide range of applications. They often operate in a highly unstable flight environment where the application of new morphing wing technologies offers the opportunity to improve flight characteristics. The investigated concept comprises port and starboard adjustable wings, and an adaptive elasto-flexible membrane serves as the lifting surface. The focus is on the benefits of the deforming membrane during the impact of a one-minus-cosine type gust. At a low Reynolds number of Re = 264000, the morphing wing model is investigated numerically by unsteady fluid–structure interaction simulations. First, the numerical results are validated by experimental data from force and moment, flow field, and deformation measurements. Second, with the rigid wing as the baseline, the flexible case is investigated, focusing on the advantages of the elastic membrane. For all configurations studied, the maximum amplitude of the lift coefficient under gust load shows good agreement between the experimental and numerical results. During the decay of the gust, they differ more the higher the aspect ratio of the wing. When considering the flow field, the main differences are due to the separation behavior on the upper side of the wing. The flow reattaches earlier in the experiments than in the simulations, which explains the higher lift values observed in the former. Only at one intermediate configuration does the lift amplitude of the rigid configuration exceeds that of the flexible by about 12%, with the elastic membrane resulting in a smaller and more uniform peak load, which is also evident in the wing loading and hence in the root bending moment.