Search Results (58)

This study investigates the aerodynamic performance of a blended multi-winglet configuration installed on the wingtip of a transonic commercial aircraft, focusing on both subsonic and transonic regimes. Conventional single winglets are typically optimized to reduce induced drag during cruise, but multi-winglets have the potential to enhance lift during takeoff and landing. However, their effectiveness in transonic conditions remains insufficiently explored. In this work, a reference Boeing 767 blended winglet was divided into three distinct elements, each retaining the original wingtip airfoil. Computational simulations were conducted to compare single- and multi-winglet configurations under cruise conditions. Additional analyses were performed at subsonic speeds to evaluate lift performance. Under transonic conditions, the multi-winglet configuration exhibited a 1.4% increase in total drag due to a greater projected frontal area. However, it achieved reduced induced drag, attributed to the rearmost winglet’s negative cant angle, which suppresses vortex formation by inhibiting upward airflow. In subsonic flight, lift improved by up to 1.3% due to accelerated flow over the upper surface, enhanced by smaller leading-edge radii and air acceleration through inter-winglet gaps. These findings suggest that multi-winglets outperform single winglets in reducing induced drag during cruise and enhancing lift during takeoff and landing. Full article

To investigate the aerodynamic characteristics and multi-objective optimization of the variable camber airfoils, the influence of leading- and trailing-edge deflections on aerodynamic performance is conducted. A novel prediction model is presented using the Kriging surrogate model, with leading and trailing edge deflection angles as inputs and lift coefficients and drag coefficients as outputs. The Non-dominated Sorting Genetic Algorithm II (NSGA II) multi-objective optimization technique is applied to ascertain the ideal deflection parameters. The results show that upward deflection of the leading edge raises the lift, whereas downward deflection increases the value of the critical angle of attack. The deflection of the trailing edge increases the value of the critical angle of attack, while the downward deflection can enhance the lift coefficient. Appropriate upward deflections of both leading and trailing edges can delay the critical Mach number, while downward deflections of both the leading and trailing edges can enhance the value of the critical Mach number. The discrepancies between the Kriging model prediction and the CFD simulation are less than 2%. Compared to the basic airfoil, the aerodynamic performance of the optimized airfoil has been improved, with the lift coefficient increasing by 7.55% and 7.37% and the lift-to-drag ratio rising by 6.97% and 10.27% at two Mach numbers, respectively. The efficiency and reliability of this method have been verified. Full article

The aerodynamic optimization of airfoil shapes remains a critical research area for enhancing aircraft performance under various flight conditions. In this study, the RAE 2822 airfoil was selected as a benchmark case to investigate and compare the effectiveness of surrogate-based methods under an Efficient Global Optimization (EGO) framework and an adjoint-based approach in both single-point and multi-point optimization settings. Prior to optimization, the computational fluid dynamics (CFD) model was validated against experimental data to ensure accuracy. For the surrogate-based methods, Kriging (KRG), Kriging with Partial Least Squares (KPLS), Gradient-Enhanced Kriging (GEK), and Gradient-Enhanced Kriging with Partial Least Squares (GEKPLS) were employed. In the single-point optimization, the GEK method achieved the highest drag reduction, outperforming other approaches, while in the multi-point case, GEKPLS provided the best overall improvement. Detailed comparisons were made against existing literature results, with the proposed methods showing competitive and superior performance, particularly in viscous, transonic conditions. The results underline the importance of incorporating gradient information into surrogate models for achieving high-fidelity aerodynamic optimizations. The study demonstrates that surrogate-based methods, especially those enriched with gradient information, can effectively match or exceed the performance of gradient-based adjoint methods within reasonable computational costs. Full article

Kolmogorov–Arnold Networks (KANs) are a recent development in machine learning, offering strong functional representation capabilities, enhanced interpretability, and reduced parameter complexity. Leveraging these advantages, this paper proposes a KAN-based reduced-order model (ROM) for unsteady aerodynamics and aeroelasticity. To effectively capture temporal dependencies inherent in nonlinear unsteady flow phenomena, an architecture termed Kolmogorov–Arnold Gated Recurrent Network (KAGRN) is introduced. By incorporating a recurrent structure and a gating mechanism, the proposed model effectively captures time-delay effects and enables the selective control and preservation of long-term temporal dependencies. This architecture provides high predictive accuracy, good generalization capability, and fast prediction speed. The performance of the model is evaluated using simulations of the NACA (National Advisory Committee for Aeronautics) 64A010 airfoil undergoing harmonic motion and limit cycle oscillations in transonic flow conditions. Results demonstrate that the proposed model can not only accurately and efficiently predict unsteady aerodynamic coefficients, but also effectively capture nonlinear aeroelastic responses. Full article

Airfoil aerodynamic design represents an essential domain in aircraft development, where the pursuit of advanced and intelligent optimization strategies is important for achieving significant advancements. In this paper, we demonstrate the effectiveness and versatility of reinforcement learning (RL)-based optimization methods in enhancing aerodynamic performance for both transonic and supersonic airfoils. We introduced a novel methodology using RL to optimize airfoil designs, leveraging ADflow as the aerodynamic solver and constructing an RL environment where Class-Shape Transformation (CST) parameters describe the airfoil geometry, transforming it into a finite state variable. Key flow field features, especially shock waves, were incorporated to guide the optimization process, enabling the RL model to iteratively improve designs based on real-time feedback from simulations. Applied to transonic airfoils, this method yielded remarkable results, including a 70.20% increase in the lift-to-drag ratio for one airfoil, with consistent improvements across various initial geometries and flight conditions. Extending to the NASA SC(2)-0404 supersonic airfoil, the optimized design achieved significant geometric changes that resulted in a 6.25% increase in the lift-to-drag ratio, with improvements ranging from 4.90% to 25.46% across different lift coefficients. These findings highlight the robustness and adaptability of RL techniques in addressing the unique challenges of both transonic and supersonic aerodynamics while maintaining structural integrity. Full article

Aerodynamic shape design optimization faces challenges due to the computational demands and the vast design space, limiting its practicality and scalability. While progress has been made in subsonic and transonic regimes, the real-time optimization for supersonic conditions remains unexplored. To bridge this gap, this work exploits knowledge learned from subsonic and transonic real-world data and introduces a rapid optimization framework tailored for the supersonic regime. A novel end-to-end multitask Convolutional Neural Network is proposed to predict the aerodynamic coefficients of an airfoil shape, extracting global and local features directly from the geometry. The surrogate model is thoroughly examined and validated, including an analysis of model explainability. The surrogate model achieves on par results with the state-of-the-art, with relative errors in aerodynamic coefficient predictions below 1.7%. Furthermore, a surrogate-based optimization strategy integrates the surrogate model with a Generative Adversarial Network to generate realistic airfoil shapes, thereby reducing the design space to a low-dimensional representation. This approach provides a robust solution that accelerates the optimization routine by over 3000 times when compared to simulation-based methods while achieving a deviation of less than 1.9% from their optimum performance. Overall, this work strikes a balance between efficiency and effectiveness without compromising reliability. Full article

It is well established that increasing vehicle efficiency enables the achievement of N + 3 sustainable air travel goals. To this end, the integration of a slotted natural-laminar-flow airfoil with a transonic, truss-based commercial wing configuration is projected to significantly decrease fuel consumption demand. The slotted natural-laminar-flow airfoil is designed with two elements to extend favorable pressure gradients further aft than single-element airfoils. This two-element design increases the extent of laminar flow to approximately 90% of the airfoil surface, thus decreasing streamwise instabilities, which in turn reduces the wing profile drag. The slotted natural-laminar-flow airfoil also exhibits the dumping-velocity effect and achieves an off-surface pressure recovery, both critical to achieving laminar flow and overcoming single-element airfoil limitations. Given the potential of this novel concept, the objective of this literature review is to discuss the history of slotted natural-laminar-flow airfoils, recent research to mature the design, and future work needed for the implementation of this airfoil on a commercial aircraft. Full article

The missions of modern aircraft require multiple abilities, such as highly efficient taking-off and landing, fast arrival, and long-endurance hovering. It is difficult to achieve all technical objectives using traditional aircraft design technology. The active flow control technology using the concept of a co-flow jet (CFJ) is a flow control method without a mass source that does not require air from the engine. It has strong flow control ability in low-speed flow, can greatly improve the stall angle of the aircraft, and can obtain large lift enhancement. At transonic conditions, it can lead to a larger lift–drag ratio with a small expense. CFJ technology has great application potential for aircraft due to its flexible control strategy and remarkable control effect. In this paper, the concept of a combination of CFJ and variable camber technology is proposed which realizes the change of airfoil camber to meet different task requirements with the movable droop head. By using the built-in ducted fan, air is blown and sucked in the jet channel so as to realize CFJ flow control. In a state of high-speed flight, complete geometric restoration is achieved by closing the channel and retracting the droop head. In this paper, the design and aerodynamic analysis of a CFJ device with variable camber based on a supercritical airfoil with small camber and a small leading-edge radius are carried out using the computational fluid dynamics (CFD) method. Comparative studies are conducted for different schemes on the taking off and landing performances, and discussions are had on core technical parameters such as power consumption. The results indicate that by utilizing the CFJ technology with more than 10 degrees of droop device, the maximum lift coefficient of a supercritical airfoil with a small camber and leading-edge radius, which is suitable for transonic flight, can be increased to a value larger than 4.0. Full article

Many real-world expensive industrial and engineering multi-objective optimization problems (MOPs) are driven by historical, experimental, or simulation data. In such scenarios, due to the expensive cost and time required, we are only left with a small amount of labeled data to perform the optimization. These offline data-driven MOPs are usually solved by multi-objective evolutionary algorithms (MOEAs) with the help of surrogate models constructed from offline historical data. The key challenge in developing these data-driven MOEAs is that they have to replace multiple conflicting fitness functions by approximating these objective functions, which may produce cumulative approximation errors and misguide the search. In order to build a reliable surrogate model from a small amount of multi-output offline data and solve the DDMOPs, we have proposed an adaptive model selection method with a reliable individual-based model management-driven MOEA. The proposed algorithm dynamically selects between DNN and XGBoost by comparing their k-fold cross-validation MAE error, which can capture the true generalization ability of the surrogates on unseen data. Then, the selected surrogate is updated with a reliable individual selection strategy, where the individual who is closest, both in the decision and objective space, to the most preferred solution among labeled offline data is chosen. As a result, these two strategies guide the underlying MOEA to the Pareto optimal solutions. The empirical results of the ZDT and DTLZ benchmark test suite validate the use of the three state-of-the-art offline DDMOEAs, showing that our algorithm is able to achieve highly competitive results in terms of convergence and diversity for 2–3 objectives. Finally, our algorithm is applied to an offline data-driven multi-objective problem—transonic airfoil (RAE 2822) shape optimization—to validate its efficiency on real-world DDMOPs. Full article

Large transport aircraft tend to adopt a wing layout with a high aspect ratio and swept-back angle due to the requirement of a high lift-to-drag ratio. Composite material is typically employed to ensure the light weight of the structure, causing serious static aeroelasticity problems to the aircraft. When the airplane is flying in the transonic region, its aerodynamic load is very complex, and the large load leads to large deformation of the wing, triggering geometric nonlinear effects, which further affects the static aerodynamic elasticity characteristics of the wing. In this study, in order to study the static aeroelastic characteristics of the transonic flow of a high-aspect-ratio airfoil, a new design method of the scaled similar optimization model is described, and the change in the model lift coefficient due to geometrically nonlinear static aeroelasticity effects when the angle of attack is changed was investigated by using simulation and wind tunnel test methods. In order to ensure the accuracy of the wing shape when the model was deformed greatly, this study employed the structural design scheme of the wing with the skin as the main stiffness component, and the thicknesses of different regions of the skin were used as the design variables for the stiffness optimization design. The engineering algorithm of nonlinear finite elements was used in this study to calculate the curve of lift with the angle of attack considering the geometric nonlinear static aeroelasticity effect. The results show that the similarity optimization process employed in this study can be used to complete the design of the high-speed aerostatic wing test model, and the wind tunnel test results show that geometric nonlinearity has a large impact on the lift coefficient of the wing. Full article

The uncertainty of the turbulence/transition model is a problem with relatively high attention in the CFD area. Wall distance is an important physical parameter in turbulence/transition modeling, and its accuracy has a large effect on numerical simulation results. As most CFD solvers use the solving strategy to calculate the nearest distance to the wall based on mesh topology, this makes wall distance one important source of the uncertainty of the simulation results. To investigate the role of wall distance in turbulence/transition simulations, we have conducted simulations for various aerodynamic shapes, such as the plate with zero pressure gradient (ZPG), RAE2822 supercritical airfoil and ONERA M6 transonic wing. Further, the prediction abilities on turbulence/transition and shock wave phenomena of several physical models, including SA, SST and Wilcox-k-ω turbulence models as well as the γ-Re_θt-SST transition model, are analyzed with different degrees of mesh orthogonality. The results imply that the numerical solution of wall distance in the boundary layer has a relatively large error when the mesh orthogonality is bad, having a large effect on the accuracy of the turbulence/transition model. In detail, the Wilcox-k-ω turbulence model is unaffected by mesh orthogonality; under the condition of mesh non-orthogonality, the SA model leads to a substantially larger friction drag and change in the location of shock wave; the SST model also leads to a larger friction drag under the condition of mesh non-orthogonality, whose effect is much less than that for SA model; and the γ-Re_θt-SST model leads to a substantial upstream shift of transition location. Full article

The zonal detached-eddy simulation (ZDES) method divides the flow field into different computational modes, offering flexibility in the simulation of complex flows. The transonic shock buffet on the upper surface of the OAT15A supercritical airfoil is numerically simulated by ZDES based on the k-ω SST model. The results show that the error in the low-frequency characteristics of the transonic shock buffet predicted by ZDES compared to experiments is within 3%. Its predictions of pressure fluctuations and averaged velocity agree better with the experimental data. Overall, ZDES is effective in predicting the periodic oscillations of shock waves along the streamwise direction, flow separation induced by shock wave motion, and the small-scale vortex structures in the wake region. Full article

To understand the asymmetric flow of a slender body with low-aspect ratio fins, a wind tunnel experiment was carried out, and the asymmetric flow was observed when the pair of fins had a symmetric deflection angle of 30° at a small angle of attack and zero sideslip angle at transonic speeds. The unsteady characteristics of flow around the moving fins, especially for the evolution of the asymmetric flow, was carefully numerically investigated via the RANS method. To verify the numerical method, the experimental steady wind tunnel data of the NACA 0012 airfoil with sinusoidal pitching motion were adopted. A hysteresis loop exists as a function of the deflection angle during the upstroke and downstroke motions. The side force is periodic due to the asymmetric flow peaks at the downstroke and their peak value appeared at around δz = 25°, which was independent of the deflection frequency. As the deflection frequency increased, the asymmetric flow formed at a higher deflection angle during the upstroke motion, but decayed at a lower deflection angle during the downstroke motion, resulting in a more significant unsteady hysteresis effect. Full article

The coupling between a transonic buffeting flow and a supercritical airfoil with harmonic heave motion was studied. A parametric space of the heave frequency and amplitude was investigated using a verified fluid–structural interaction framework. The spatial-temporal flow pattern around the transonic airfoil was studied using dynamic mode decomposition (DMD) to unveil the physical coupling mechanism. The results show three types of flow responses under the heave motion: (I) A buffet frequency response with a $\lambda$-shape shock wave structure and recirculation zone at the shock foot. The aerodynamic performance was alike the scenario in the flow past the stationary airfoil. (II) A transitional response with a weakened shock and enhanced boundary layer. The aerodynamic performance deteriorated sharply at $f=f_{\mathrm{buffet}}$ and recovered after the frequency was past the buffet frequency. The flow pattern was characterized by a double-shock structure that interacted with the enhanced boundary layer. (III) A heave frequency response with the dominant heave motion. The variance in the aerodynamic loading increased significantly at $f>f_{\mathrm{buffet}}$ and there were higher heave amplitudes in this stage. The driving motion of the airfoil transferred the energy of the buffet mode to the boundary layer with a more even energy balance according to the energy contribution analysis of the DMD modes. Full article

Transonic buffet flow is a classical complex and unstable flow that has a negative effect on aircraft fly safety. Therefore, it is crucial to study the unsteady characteristics of buffet flow. The numerical analysis method is very useful in achieving the aforementioned goal. In this paper, focused on the typical supercritical airfoil OAT15A in fixed and pitching conditions, unsteady Reynolds averaged Navier–Stokes (URANS) closed with the sst-kω turbulence mode, coupled with the structure dynamical equation, is utilized to investigate the transonic buffet flow. Firstly, from the perspective of coherent flow structure, flow velocity divergence snapshots constructed from unsteady flow solutions are used to analyze the feature of transonic buffets in the two cases mentioned. Then, DMD modes are extracted by the dynamic mode decomposition technique from the velocity snapshots and adopted to analyze the flow modes of the two distinct flow fields. The numerical simulation results show that, in the fixed case, the regular motion feature of the buffet is present, the shock oscillation is closely related to the vortex structure, and the durations of rearward and forward movements of the shock are both equal to half of the buffet period. In the pitching case, the duration of the rearward motion of the primary shock is approximately five eighths of one buffet period, and the secondary shock appears with the primary one moving downstream, and they interact with each other. The region of the shock movement is larger than that of the fixed case, and there is chaotic flow rather than periodic flow in its wake. Structural elastic oscillation changes the characteristics of the aerodynamic response, which is solely affected by the frequency of the pitching oscillation. Full article