Supercritical Airfoil Research Articles

Advancing buffet onset prediction: a deep learning approach with enhanced interpretability for aerodynamic engineering

The interaction between the shock wave and boundary layer of transonic wings can trigger periodic self-excited oscillations, resulting in transonic buffet. Buffet severely restricts the flight envelope of civil aircraft and is directly related to their aerodynamic performance and safety. Developing efficient and reliable techniques for buffet onset prediction is crucial for the advancement of civil aircraft. In this study, utilizing a comprehensive database of supercritical airfoils generated through numerical simulations, a convolutional neural network (CNN) model is firstly developed to perform buffet classification based on the flow fields. After that, employing explainable machine learning techniques, including Gradient-weighted Class Activation Mapping (Grad-CAM), random forest algorithms, and statistical analysis, the research investigates the correlations between supervised CNN features and key physical characteristics related with the separation region, shock wave, leading edge suction peak, and post-shock loading. Finally, physical buffet onset metric is established with good generalization and accuracy, providing valuable guidance for engineering design in civil aircraft.

Prediction of Transonic Shock Buffet over Supercritical Airfoil OAT15A Based on Zonal Detached-Eddy Simulation

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.

Behaviour of Whitcomb Integral Supercritical airfoil at various angles of attack in sonic condition using CFD

Understanding the aerodynamic behaviour of an airfoil is crucial for evaluating its performance in generating lift and drag. In this study, the aerodynamic performance of the Whitcomb Integral Supercritical Airfoil is analysed across a range of angles of attack—specifically, 2°, 4°, 6°, 8°, and 10°—under sonic conditions. The primary objective is to investigate and characterize the lift and drag properties exhibited by the airfoil at these various angles of attack. This analysis will provide insights into how the airfoil performs in terms of efficiency and stability at sonic speeds.

Numerical Simulation of Circulation Control for a Wing Section Using Coanda Jets

Large-eddy simulations were carried out to describe the subsonic flow over a wing section, using Coanda-jet circulation control to augment lift. The section geometry consists of a modified supercritical airfoil, with a jet that is blown over a one-quarter circular cylindrical trailing-edge Coanda surface. Because the configuration does not include a slotted trailing-edge flap, the mechanical complexity and weight may be reduced. The computations correspond to an experimental investigation, which provides data for comparison. High-fidelity solutions were obtained to the unsteady three-dimensional Navier–Stokes equations at a chord-based Reynolds number of 4.75×105 and freestream Mach number of 0.1. Several angles of attack were considered, and solutions were obtained both with and without circulation control. In the control cases, three different jet-mass flow rates were simulated at each angle of attack. A grid-resolution study was carried out to assure numerical accuracy. Comparisons are made between the respective cases and with the experimental data, and features of the flowfields are characterized. It was found that Coanda-jet control was able to augment lift in excess of factors of three with reasonable amounts of jet-mass flow.

Coupling Analysis between the Transonic Buffeting Flow and a Heaving Supercritical Airfoil Based on Dynamic Mode Decomposition

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 λ-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=fbuffet 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>fbuffet 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.

Optimizing Obscurity: Advancing Stealth Capabilities and Performance of BWB Fighter with Symmetric Supercritical Airfoils

Optimizing Obscurity: Advancing Stealth Capabilities and Performance of BWB Fighter with Symmetric Supercritical Airfoils

Spatial And Temporal Modes On A Generic Tandem Configuration In Transonic Shock Buffet

Certain combinations of upstream flow conditions in transonic flight may incite a highly unsteady shock-wave/boundary-layer interaction, often referred to as transonic buffet. The coupling of periodic shock motion and intermittent separation is seen to convey a characteristic unsteadiness in the evolution of the turbulent wake. This article uses high-speed focusing Schlieren and PIV measurements at high spatial resolution to characterize the temporal and spectral modes governing the flow past a generic 2D tandem configuration. This interaction, consisting of an OAT15A supercritical airfoil as the main wing and a NACA 64A-110 profile representing the tailplane, is investigated at chord-based Reynolds numbers of 2 million and 1 million, respectively and compared against fully-established shock buffet conditions in an isolated airfoil scenario operated at identical inflow conditions. The strongest buffet is observed in both configurations for a Mach number of 0.72 and an angle of attack of 5 deg, occurring at frequencies of 112 Hz and 103 Hz. Despite an equally periodic nature of the buffet unsteadiness, both shock amplitude and frequency are seen to decrease slightly in the tandem interaction. Global spectral analysis performed on the entire field of view identifies the buffet instability as the governing mode in both flow scenarios, imposing its unsteadiness even far downstream of its origin, allowing the extraction. of relevant sensor locations for a subsequent localized assessment of the involved time scales. Except for the buffet mode, complementing DMD analyses reveal a strong influence of a vortex-shedding mode throughout the entire buffet cycle. Mode shapes and associated frequencies furthermore suggest an intermittent low-frequency/large wavelength and high-frequency/low wavelength behavior, involving leading contributions between 2000 Hz and 4000 Hz.

On the Lock-In Phenomena near the Transonic Buffet Onset of a Prescribed Pitching Airfoil

The limit cycle oscillation (LCO) in the transonic buffet on the fixed supercritical airfoil OAT15A under Ma = 0.73, AoA = 3.5° and Re≈3×106, is successfully simulated by means of the Reynolds Stress Model. Further, the buffet lock-in phenomena under prescribed pitch conditions near the buffet onset are also studied by evaluating the modified energy exchange based on the pitching component of the moment coefficients as well as the normalized relative phase map between the pitching component of the moment coefficients and the airfoil’s angular velocity. The zero energy transfer branches in the modified energy map fail to indicate the lock-in boundaries, while the normalized phase map generally outlines the lock-in boundaries for small pitch amplitudes near the buffet onset, which suggests that the lock-in occurs where the moment is in phase with the angular velocity at small pitch amplitudes near the buffet onset. For pitch amplitudes larger than 0.4°, the lock-in onset deviates from the phase shift, possibly due to the fact the instantaneous angle of attack can be lower than the buffet onset where the buffet phenomena may vanish.

Investigation on Flow over Conventional and Supercritical Airfoils at Transonic Regimes

Investigation on Flow over Conventional and Supercritical Airfoils at Transonic Regimes

Comparative analysis of compressible inviscid flow over symmetric and supercritical airfoil

Studying compressible inviscid flow over symmetric and supercritical airfoils is important because it is useful to understand and maximize aerodynamic performance in a range of industrial contexts. This study addresses the analysis of symmetric and supercritical airfoils for compressible inviscid flow for both time-dependent and stationary scenarios. The primary goal of these simulations’ is to look at how different velocity variations affected certain airfoil parameters. Air is utilized as the material above airfoils. The best fit for these simulations is the Spalart-Allmaras Turbulence model, which shows good agreement over a wider velocity range with published experimental data from other studies. The COMSOL Multiphysics software is used for all the analysis, for angle of attack 0°, temperature 288K, pressure 1bar and the airfoils that are constructed by importing airfoil data file in COMSOL in the form of excel file. On the comparison of compressible inviscid flow, the supercritical airfoil has better results on the basis of velocity magnitude, pressure, vorticity magnitude, shear rate and rotation rate. The results are converging faster in supercritical airfoil than symmetric airfoil. At a zero-degree angle of attack, velocity increases more on the suction side while decreases on the pressure side (bottom). The final solution error for supercritical airfoil is 1.6E-05, while final residual error for “velocity u pressure p” is 1.2E-05. For symmetric airfoil, final solution error is 0.15, although final residual error is 2.6. Based on the error plot, it decreases rapidly in case of supercritical with a range from 100 to 10-4. Additionally, the wall resolution is constructed for both cases i.e., symmetric airfoil and supercritical airfoil. The main result is that ,with the passage of time, the flow is becoming to stationary state. In the end, model validation via comparison with experimental data highlights the validity and applicability of the results.

Design and Validation of the Trailing Edge of a Variable Camber Wing Based on a Two-Dimensional Airfoil.

Variable camber wing technology stands out as the most promising morphing technology currently available in green aviation. Despite the ongoing advancements in smart materials and compliant structures, they still fall short in terms of driving force, power, and speed, rendering mechanical structures based on kinematics the preferred choice for large long-range civilian aircraft. In line with this principle, this paper introduces a linkage-based variable camber trailing edge design approach. Covering coordinated design, internal skeleton design, flexible skin design, and drive structure design, the method leverages a two-dimensional supercritical airfoil to craft a seamless, continuous two-dimensional wing full-size variable camber trailing edge structure, boasting a 2.7 m span and 4.3 m chord. Given the significant changes in aerodynamic load direction, ground tests under cruise load utilize a tracking-loading system based on tape and lever. Results indicate that the designed single-degree-of-freedom Watt I mechanism and Stephenson III drive mechanism adeptly accommodate the slender trailing edge of the supercritical airfoil. Under a maximum cruise vertical aerodynamic load of 17,072 N, the structure meets strength requirements when deflected to 5°. The research in this paper can provide some insights into the engineering design of variable camber wings.

Numerical Study of Transonic Buffet on SC(2)-0518 and OAT15A with Vortex Generators

Predicting the transonic buffet and its onset is important for ascertaining the performance limits of an aircraft at its critical angle of attack. Additionally, a physical understanding of the buffet suppression technique is important for preventing shock wave oscillations. In this study, we conducted zonal detached-eddy simulations to numerically investigate the effects of vortex generators (VGs) on buffet suppression and to discuss the differing flow characteristics of the SC(2)-0518 and OAT15A supercritical airfoils when the chordwise position of the VGs is varied. The results for both airfoils equipped with VGs demonstrated significant suppression of large-scale lift oscillations across all calculation steps. VGs placed at 10% of the chord (10%c) from the leading edge produced higher time-averaged lift coefficients for both airfoils, with the OAT15A airfoil showing a particularly notable 2.5% improvement in lift coefficient, leading to a 0.82% increase in L/D ratio. The visualized results indicated that the interaction between the shock wave and VGs leads to variations in the separation point, depending on the VG chordwise position. This separation is affected by the aerodynamic characteristics of the airfoil shapes and the wake induced by the VGs, ultimately resulting in changes to the lift coefficient.

Fast Buffet-Onset Prediction and Optimization Method Based on Pretrained Flowfield Prediction Model

A transonic buffet is a detrimental phenomenon that occurs on supercritical airfoils and limits the aircraft operating envelope. Traditional methods for predicting buffet onset rely on multiple computational fluid dynamics simulations to assess a series of airfoil flowfields and then apply criteria to them, which is slow and hinders optimization efforts. This study introduces an innovative approach for rapid buffet-onset prediction. A machine-learning flowfield prediction model was pretrained on a large database and then deployed offline to replace the simulations in the buffet prediction process for new airfoil designs. Unlike using a model to directly predict buffet onset, the proposed technique offers better visualization capabilities by providing users with intuitive flowfield outputs. It also demonstrates superior generalization ability, as evidenced by a 32.5% reduction in the average buffet-onset prediction error on the testing dataset. This method was used to optimize the buffet performance of 11 distinct airfoils within and outside the training dataset. The optimization results were verified with simulations and proved to yield improved samples across all cases. It was affirmed that the pretrained flowfield prediction model can be applied to accelerate aerodynamic shape optimization, but further work is still needed to raise its reliability for this safety-critical task.

Virtual leading-edge aero-shaping of an airfoil using a dielectric barrier discharge plasma actuator

Recently, it has been demonstrated that dielectric barrier discharge plasma actuators, which can be capable of generating a quasi-steady wall jet under the effect of a sinusoidal power supply, are well suitable for controlling the flow around the airfoil at a low Reynolds number. To uncover the controlling mechanism of plasma actuators, flow separation control over an SC (2)-0714 supercritical airfoil using an asymmetrical plasma actuator arranged at the leading edge of the airfoil, is studied at Reynolds number of 7.8 × 104. The stall angle of attack is delayed from 9° to 13°, and the maximum lift coefficient is increased by about 27%. In addition to the momentum injection to the boundary layer, which is one of the control mechanisms and can be achieved by the induced spanwise vortex of the plasma actuator, the closed recirculation region, which is similar to superimposing a hump on the leading edge of the airfoil, is another control mechanism, leading to an increase in the effective camber of the airfoil. The localized recirculation zone, which is created by the plasma actuator and modifies the leading-edge aero-shaping and results in the enhancement of the lift coefficient, is first observed, and this effect of the plasma actuator is called the virtual leading-edge aero-shaping.

Mesh-Agnostic Decoders for Supercritical Airfoil Prediction and Inverse Design

Mesh-agnostic models have advantages in terms of processing unstructured spatial data and incorporating partial differential equations. Recently, they have been widely studied for constructing physics-informed neural networks, but they need to be trained on a case-by-case basis and require long training times. On the other hand, fast prediction and design tools are desired for aerodynamic shape designs, and data-driven mesh-based models have achieved great performance. Therefore, this paper proposes a data-driven mesh-agnostic decoder that combines the fast prediction ability of data-driven models and the flexibility of mesh-agnostic models. The model is denoted by an implicit decoder, which consists of two subnetworks, i.e., ShapeNet and HyperNet. ShapeNet is based on implicit neural representation, and HyperNet is a simple neural network. The implicit decoder is trained for the fast prediction of supercritical airfoils. Different activation functions are compared, and a spatial constraint is proposed to improve the interpretability and generalization ability of the model. Then, the implicit decoder is used together with a mesh-based encoder to build a generative model, which is used for the inverse design of supercritical airfoils with specified physical features.

Data-driven prediction of aerodynamic noise of transonic buffeting over an airfoil

Accurately predicting buffet frequency and aerodynamic noise level is crucial in transonic buffet noise reduction studies. In this study, the Random Forest (RF) algorithm is employed to predict the Power Spectral Density (PSD) and Overall Sound Pressure Level (OASPL) distribution over the supercritical airfoil RAE2822. The study indicates that the RF algorithm exhibits greater advantages over the Multi-Layer Perceptron (MLP). This algorithm does not suffer from the problems of high-frequency divergence or inflection distortion, maintaining a reduction in prediction errors for OASPL and PSD by approximately three to four orders of magnitude. Additionally, this paper proposes a priori criterion for evaluating the accuracy of PSD prediction. When there is a strong correlation between PSD at adjacent points, a data-driven modeling approach can achieve higher prediction accuracy. However, when the root mean square error of the cross-correlation functions, auto-correlation functions, and the PSD between adjacent points are both high, the generalization ability of pure data-driven modeling is insufficient, necessitating the additional monitoring points to ensure prediction accuracy.

A deep reinforcement learning optimization framework for supercritical airfoil aerodynamic shape design

A deep reinforcement learning optimization framework for supercritical airfoil aerodynamic shape design

Fluidic Flow Control Devices for Gust Load Alleviation

A reduction in the structural weight and climate-relevant emissions of future transport aircraft can be realized through active gust load alleviation, limiting the peak aerodynamic loads experienced in flight. Two fluidic concepts, surface and Coandă jets, offer promising solutions. The surface jet induces a separated flow region on the wing’s suction side near the trailing edge, while the Coandă jet utilizes tangential blowing over a rounded trailing edge to make use of the Coandă effect for direct circulation control. This study investigates these fluidic actuation concepts using two-dimensional unsteady Reynolds-averaged Navier–Stokes simulations on a supercritical airfoil to alleviate gust-induced lift increases. Results reveal that fluidic concepts can surpass the load reduction capability of a trailing edge flap. Notably, the Coandă-type design, while more efficient, exhibits limited control authority compared to surface jet, achieving maximum gust load reductions of 40% versus 70% for surface jet. Optimizing the temporal deployment of the surface jet leads to increased peak lift reduction. Even under challenging conditions with reduced gust anticipation time and actuator placement near the wing tip with a reduced chord length, the surface jet maintains consistent performance and therefore offers a promising solution for active gust load alleviation on future aircraft.

Hovering performance analysis of helicopter rotor blades using supercritical airfoil

PurposeThis study aims to find the characteristics of supercritical airfoil in helicopter rotor blades for hovering phase using numerical analysis and the validation using experimental results.Design/methodology/approachUsing numerical analysis in the forward phase of the helicopter, supercritical airfoil is compared with the conventional airfoil for the aerodynamic performance. The multiple reference frame method is used to produce the results for rotational analysis. A grid independence test was carried out, and validation was obtained using benchmark values from NASA data.FindingsFrom the analysis results, a supercritical airfoil in hovering flight analysis proved that the NASA SC rotor produces 25% at 5°, 26% at 12° and 32% better thrust at 8° of collective pitch than the HH02 rotor. Helicopter performance parameters are also calculated based on momentum theory. Theoretical calculations prove that the NASA SC rotor is better than the HH02 rotor. The results of helicopter performance prove that the NASA SC rotor provides better aerodynamic efficiency than the HH02 rotor.Originality/valueThe novelty of the paper is it proved the aerodynamic performance of supercritical airfoil is performing better than the HH02 airfoil. The results are validated with the experimental values and theoretical calculations from the momentum theory.

Ice sensitivity analysis of different airfoils

When an aircraft passes through clouds containing supercooled water droplets, it condenses into ice on the surface of the wing. Wing icing will reduce the flight envelope of the aircraft as a whole, limit the flight range and speed, and threaten flight safety. The range and intensity of icing are not only determined by meteorological conditions but also closely related to the types of airfoils. In order to study the influence of airfoils on icing, GAW-2 high lift airfoil, NLF (1)-0215F natural laminar airfoil and SC (2)-0714 supercritical airfoil are selected as the representatives of the three mainstream airfoils. The Numerical simulation method is used to analyze the influence of icing parameters on the three airfoils, summarize the icing rules and analyze the differences.