Explore the vast range of titles available.

This paper introduces a generic model for the study of aerodynamic behaviour relevant to fifth-generation high-performance aircraft. The model design is presented, outlining simplifications made to retain the key features of modern high-performance vehicles while ensuring a manufacturable geometry. Subsonic wind tunnel tests were performed with force and moment balance measurements used to develop a database of experimental validation data for the platform at a freestream velocity of 20 m/s. Numerical simulations are also presented and validated by the experiments and further employed to ensure the vortex behaviour is consistent with contemporary high-performance platforms. A sensitivity study of the computational predictions from the turbulence modelling approach is also presented. This geometry is the first in a suite of representative aircraft geometries (the Sydney Standard Aerodynamic Models), in which all geometries, computational models, and experimental data are made openly available to the research community (accessible via this link: https://zenodo.org/communities/ssam_gen5/) to serve as validation test cases and promote best practices in aerodynamic modelling.

This paper presents an investigation of flow asymmetry around a slender body at high angles of attack. The paper investigated the numerical aspect of simulating such flows. The impact of three simulation parameters, including grid resolution, discretization scheme, and turbulent flow modeling, was assessed. It was shown that insufficient grid density resulted in highly dissipated solution. At high angles, where flow asymmetry is expected to develop around the body, the dissipation from poor grid resolution prevented the flow asymmetry. At higher grid resolution, the solution demonstrated a switch between two bistable states. Two spatial discretization schemes, namely central and bounded, were tested in the course of this study. The results illustrated the necessity to use non-dissipative unbiased discretization schemes. Large eddy simulation was performed using two sub-grid-scale models in addition to a run without a model. The sub-grid-scale models generated similar results except for switching of asymmetry direction and the axial location of separation foci. The study shows that grid resolution and solution scheme have a profound effect on the validity of the simulation of flow around slender bodies at high angles of attack. The study also showed that stringent grid requirements marginalized the effect of the sub-grid-scale model. Computations were then carried out at seven angles of attack \\[\\alpha = 30^{\\circ }\\], \\[40^\\circ \\], \\[50^\\circ \\], \\[52.5^\\circ \\], \\[55^\\circ \\], \\[57.5^\\circ \\], and \\[60^\\circ \\]. Analysis was performed on mean and unsteady flow fields. The total normal force increased with increasing angle of attack. On the other hand, the total side force started to increase rapidly for angles of attack \\[\\alpha > 50^{\\circ }\\] and reached a maximum at \\[\\alpha =57.5^{\\circ }\\] before decreasing at \\[\\alpha =60^{\\circ }\\]. A bistable mode was observed for \\[\\alpha > 50^{\\circ }\\] in which the orientation of resultant forces switches with angle of attack. Comparison of computed dominant frequencies with experiment showed an acceptable agreement. Several dominant modes were identified: very low-frequency mode, low-frequency mode, intermediate-frequency mode, and high-frequency mode. The modes were shown to develop with increasing angle of attack. Surface flow pathlines revealed the existence of separation foci at \\[\\alpha =57.5^{\\circ }\\] and \\[60^{\\circ }\\], and a high-frequency tonal mode was observed to accompany the formation of separation foci.

Airfoil slots, as a passive flow control technique-based wing improvement structure, may successfully delay the stall angle and increase the lift coefficient in situations with a high angle of attack. But when the angle of attack is minimal, it drastically reduces the airfoil’s initial aerodynamic performance. The NACA4412 airfoil is used as the research object in this study, which uses Computational Fluid Dynamics (CFD) techniques to examine how various slot configurations affect the airfoil’s aerodynamic properties. Based on the optimal slot configuration, a scheme for dynamically adjusting the slot angle is proposed. The research results demonstrate the following: 1) Compared to previous configurations, Slot Configuration III may greatly enhance the airfoil’s stall characteristics by postponing the stall angle to 24° and raising the maximum lift coefficient by 27.6% to 1.57; 2) Through the rotation of the leading edge, the study achieved changes in slot configuration and inlet/outlet parameters, resulting in two slot configurations capable of maintaining aerodynamic performance under small angles of attack; 3) Utilizing the geometric relationship between Slot Configurations III and IV (5°, 8°), a variable-angle slot scheme is proposed, which enhances small angle of attack lift while effectively suppressing stall phenomena.

Shock buffet on wings encountered in edge-of-the-envelope transonic flight remains an unresolved and disputed flow phenomenon, challenging both fundamental fluid mechanics and applied aircraft aerodynamics. Its dynamics is revealed through the interaction of spanwise shock-wave oscillations and intermittent turbulent boundary-layer separation. Resulting unsteady aerodynamic loads, and their mutual working with the flexible aircraft structure, need to be accounted for in establishing the safe flight envelope. The question of global instability leading to this flow unsteadiness is addressed herein. It is shown for the first time on an industrially relevant configuration that the dynamics of a single unstable oscillatory eigenmode plays a prominent role in near-onset shock buffet on a quasi-rigid wing. Its three-dimensional spatial structure, previously inferred both from experiment and time-marching simulation, describes a spanwise-localised pocket of shear-layer pulsation synchronised with an outboard-propagating shock oscillation. The results also suggest that the concept of a critical global shock-buffet mode commonly reported for two-dimensional aerofoils also applies to three-dimensional finite and swept wings, albeit different modes at play. Specifically, the modern wing design, NASA Common Research Model, with publicly available geometry and experimental data for code validation is studied at a free-stream Mach number of 0.85 with Reynolds number per reference chord of$5.0\\times 10^{6}$and varying angle of attack between 3. 5 ° and 4. 0 ° targeting the instability onset. Strouhal number at instability onset just above 3. 7 ° is approximately 0.39. At the same time, a band of eigenmodes shows reduced decay rate in the Strouhal-number range of 0.3 to 0.7, with additional unstable oscillatory modes appearing beyond onset. Importantly, those emerging modes seem to discretise the continuous band of medium-wavelength modes, as recently reported for infinite swept wings using stability analysis, hence generalising those findings to finite wings. Through conventional time-marching unsteady simulation it is explored how the critical linear eigenmode feeds into the nonlinearly saturated limit-cycle oscillation near instability onset. The established numerical strategy, using an iterative inner–outer Krylov approach with shift-and-invert spectral transformation and sparse iterative linear solver, to solve the arising large-scale eigenvalue problem with an industrial Reynolds-averaged Navier–Stokes flow solver means that such a practical non-canonical test case at a high-Reynolds-number condition can be investigated. The numerical findings can potentially be exploited for more effective unsteady flow analysis in future wing design and inform routes to flow control and model reduction.

This paper focuses on the discovery of optimal flapping wing kinematics using a deep learning surrogate model for unsteady aerodynamics and multi-objective optimisation. First, a surrogate model of the unsteady forces experienced by a 3-D flapping wing is built, based on deep neural networks. The model is trained on a dataset of randomly generated kinematics simulated using direct numerical simulation (DNS). Once trained, the neural networks can quickly predict the unsteady lift and torques experienced by the wing, using sparse information on the kinematics. This fast surrogate model allows multi-objective optimisation to be performed. The resulting Pareto front consists of new kinematics that may be very different from the kinematics of the initial dataset. A few arbitrarily chosen kinematics on the Pareto front are thus simulated using DNS and used to enhance the database. The new dataset is used to train again the networks, and this active deep learning/optimisation framework is performed until convergence, obtained after only two iterations. Overall, this method reduced the cost of optimisation by 83 %. Results reveal two distinct families of motions. Kinematics promoting high efficiency are characterised by large stroke amplitudes and relatively low angles of attack, as observed for fruit flies, honeybees or hawkmoths. For those, lift production is driven by quasi-steady effects and the formation of a stable leading edge vortex. Kinematics promoting high lift are characterised by small stroke amplitudes and high angles of attack, reminiscent of mosquitoes. Lift production is driven by the rapid generation of vorticity at the trailing edge.

Dynamic stall is an unsteady flow separation phenomenon. When the rotor flies forward, a dynamic stall caused by a high angle of attack will occur on the retreating blade. In contrast, dynamic stalls caused by shock-induced leading-edge separation will occur on the advancing blade. Dynamic stalls will lead to serious vibration load on the body and affect the service life. Rotor blades are always accompanied by pitching motion and plunging motion. In the past, the aerodynamic calculation of blades often ignored the influence of plunging motion. In this paper, a numerical calculation model is established by using the overlapping grid and computational fluid dynamics (CFD) method, which can consider the unsteady aerodynamic characteristics of airfoil pitching and plunging motion at the same time. Through the study of the aerodynamic parameters of the plunging motion airfoil, the aerodynamic difference between the two motion modes and its influence on the dynamic characteristics of the helicopter rotor is revealed. The unsteady aerodynamic calculation of the pitching and plunging motion of the NACA0012 airfoil and the NACA23012 airfoil is carried out, respectively, which verifies the accuracy and feasibility of the CFD model in this paper. The plunging motion of the NACA23012 airfoil is equivalent to the pitching motion, and the aerodynamic characteristics of the plunging motion are further analyzed. The lift characteristics calculated by the two motion modes are close, but the moment characteristics are significantly different. Increasing the plunging amplitude and the incoming Mach number, the moment difference is further amplified, and the aerodynamic calculation of the rotor blade is not suitable for the pitching motion equivalent to the plunging motion.

A high-speed train with wings (HSTW) is a new type of train that enhances aerodynamic lift by adding wings, effectively reducing gravity, to reduce the wear and tear of wheels and rails. This study, based on the RNG k−ε turbulence model and employing a sliding grid method, investigates the aerodynamic effects of HSTWs with different angles of attack when passing through tunnels. The precision of numerical simulation method is validated by data obtained through a moving model test. The results show that the lift of the HSTW increases upon entering the tunnel, with an average lift in the tunnel of 33.3% greater than that in the open air. The angle of attack is reduced from 12.5° to 7.5° when the train enters the tunnel, which can better reduce the lift fluctuations and concurrently also reduce the peak-to-peak pressure on the surface of the train and the tunnel, which is conducive to the train passing through the tunnel smoothly; hence, the angle of attack for the HSTW when passing through a tunnel is adjusted 7.5°. Furthermore, a comparison between the high-speed trains with and without wings demonstrates that the frontal pressure of the trains increases due to the blockage effect caused by the wings, while the rear of the trains experiences decreased pressure, which is primarily influenced by the wing wake. The outcomes of this study provide technical support for HSTWs passing smoothly through tunnels.

Solar-powered drones typically use flexible thin film material as skin materials to adapt to the high aspect ratio and low wing load wings. However, the thin film undergoes elastic deformation under aerodynamic loads, resulting in uncertain effects on the aerodynamic characteristics. To verify which turbulence model has higher prediction accuracy for the low Reynolds number aerodynamic characteristics of thin film wings, this paper conducted fluid-structure coupling analysis on thin film wings using both the S-A model and the Transition SST model. The influence of turbulence models on numerical analysis results was studied by comparing them with wind tunnel test results. The results indicate that: (1) Both models have high prediction accuracy for lift; (2) At low angles of attack, the two models have higher accuracy in predicting drag, while at high angles of attack, the predictive accuracy sharply decreases, and the S-A model has higher accuracy; (3) The prediction accuracy of pitch moment by the two models is worse than that of lift, while the Tran-SST model has higher accuracy. This has reference value for studying the aerodynamic characteristics of solar-powered drones.

Inspired by the wave-rider idea and momentum principle, the vehicle with inverted dihedral and momentum lift augmentation is a new aerodynamic configuration of high-speed gliding vehicle in the near-space, which has achieved a high lift-to-drag ratio and long-distance sliding. Numerical simulation of aerodynamic characteristics and stability of the aircraft are carried out in this paper. The lift-to-drag characteristics, longitudinal-directional stability and lateral-directional stability are evaluated based on the National Numerical Wind tunnel’s high-speed simulation software, named NNW-HyFLOW. An unstructured/hybrid grid is used in the calculation at the typical ballistic points of altitude of 10-75km and Mach number of 3-25. The results shows that the lift-to-drag ratio reaches a peak value of 4.11 at the altitude of 30km and attack angle of 8°. This value is decreased when the altitude raises. The usable lift-to-drag ratio is over 3 in the glide phase range from 30 to 50 kilometres. This vehicle shows better longitudinal-directional stability at large angles of attack than at small in the reentry phase and glide phase, which can be optimized by adjusting the center of mass or pitching rudder. It has a weak instability in the lateral direction at small angle of attack in the glide phase. Therefore, it is suggested to avoid to work at the high altitude with a small angle of attack. Or, the lateral-directional stability can be strengthened at this altitude by improving the V-tail.

Directly obtaining the dynamic values of the unsteady aerodynamics at large angle of attack by either the CFD or experimental technologies to present further analysis should pay great costs. Therefore, the unsteady aerodynamic modeling based on a few calculations or experimental data has been established and developed. This study mainly discusses the development and challenges of unsteady aerodynamic modeling of aircraft at high angle of attack, investigates the accuracy, efficiency, and future development of the conventional and modern intelligent models divided according to the established physical basis. The conventional methods have been built on valuating changing law of either the macroscopic aerodynamic performance or microscopic flow separating characteristics, which is mainly composed of linear/nonlinear aerodynamic derivative model, integrated models, differential models, aerodynamic incremental model and angular rate model. The intelligent methods are represented by fuzzy logic, support vector machines and shallow / deep neural network models, all of which are proposed by training the sample data based on various intelligence algorithms. Compared to the conventional aerodynamic models, these intelligent models have strong generalization ability and high predication efficiency. However, they are poorly interpretable due to the lack of physical basis on the dynamic flow fields. In general, the future unsteady aerodynamic models should be developed by focusing on the intelligently characterization of physical meaning of the nonlinear dynamic flow fields to improve the predication accuracy and efficiency on the complex aerodynamic forces/moments, and the applications in aircraft design and flight dynamics.