High Angles Of Attack Research Articles

Study on vortex-induced vibration response of large-scale two-lay steel trusses bridge under large wind angle of attack

With the advancement of urbanization, two-lay trusses bridges are widely used because of their good traffic capacity and structural performance. However, the aerodynamic behavior of this beam type is still in the exploratory stage. The local microclimate characteristics at the bridge site in mountainous cities are obvious, and it is easy to form a large wind angle of attack, which has a significant impact on the vortex-induced vibration (VIV) performance of the bridge. Therefore, this study takes a long-span two-lay steel trusses bridge in a mountainous city as the engineering background, and uses wind tunnel test and numerical calculation methods to study the changes of the static three-component force coefficient and VIV response of the main beam in the construction and completion state under the action of high wind angle of attack. The results show that the three-component force coefficient curves under different wind speeds are close to each other, and the Reynolds number effect is not obvious. The vibration test shows that the vertical bending VIV first occurs at +3° and +5°, and then two torsional VIV with different amplitudes occur. Both vertical bending and torsional VIV are simple harmonic vibrations with a single frequency, and the vertical bending VIV frequency is locked at 2.227 Hz, and the torsional VIV frequency is locked at 4.289 Hz, which are close to the natural frequency of the test model. Compared with +3°, the maximum amplitude of vertical bending VIV under +5° increases by 30.0 %, while the maximum amplitude of torsional VIV under high and low wind speed increases by 16.6 % and 12.7 % respectively, and the locking range is longer. It can be seen that the wind angle of attack has a significant effect on the VIV response of the main beam in the completion state. Especially, the trusses beam at a large angle is more sensitive to VIV, and it is more prone to large-scale and large-amplitude VIV. The research results can provide a theoretical basis for the aerodynamic shape optimization and provide a reference for the design of related bridges.

Detached Eddy Simulation of Micro-Vortex Generators Mounted on NACA 4412 Airfoil

Abstract Micro Vortex Generators (MVGs) are simple vane-type devices installed on surfaces i.e. aircraft wing and tail, to control boundary layer flow separation. They are cost-effective and require an efficient numerical method to resolve the embedded longitudinal vortical structure, as the flow behind them is highly unsteady. This numerical study aims at analyzing the effect of MVGs on the NACA 4412 airfoil performance using the detached eddy simulation (DES) at 60,000 Reynolds number based on the free stream velocity of 11 m/s and the wing chord of 0.1 meter. The MVGs are installed in a row in counter-rotating configuration at 10% chord of the airfoil. The DES is utilized to resolve the high energetic scales of the vortex behind the MVGs which Reynolds Averaged Navier-Stokes (RANS) is not likely to resolve properly. A comparison of DES simulations with the RANS simulations shows that RANS modeling is not sufficient to capture the airfoil flow characteristics at higher angles of attack. The DES simulations resolve the turbulent scales downstream of the MVGs effectively and produce significant improvement in NACA 4412 wing performance. It has been observed that airfoil lift coefficient at 10 degree angle of attack with the MVGs is 5% higher than the airfoil without MVGs. MVGs along the airfoil chordwise location demonstrate that MVGs at 25% chord are more effective in managing separation over the airfoil compared to those at 10% chord location.

The influence of trailing edge flaps on the aerodynamic characteristics of S1223 aerofoil

The S1223 aerofoil is a low Reynolds number high lift aerofoil. Analysing the aerodynamic characteristics of this aerofoil can provide a theoretical basis for enhancing flight efficiency in the design of small unmanned aerial vehicles. This study employed the k--SST turbulence model in the fluid simulation software (ANSYS Fluent) to conduct two-dimensional numerical aerodynamic simulations on the original aerofoil and its modified versions, which included flaps (deflected 10 at 70% chord length) and slotted flaps (deflected 10 at 70% chord length with a slot width of 1.5% of the chord). The aerofoil's aerodynamic performance was confirmed by comparing lift and drag coefficients at different angles of attack under Reynolds number 5.0105, as well as by analysing the pressure and velocity gradients in the flow field. The results indicate that both the lower flap and the slotted flap can greatly enhance the lift-to-drag ratio. In contrast, slotted flaps delay boundary layer separation, providing greater lift at high angles of attack while reducing the impact on drag.

A New Grid-Slat Fusion Device to Improve the Take-Off and Landing Performance of Amphibious Seaplanes

To reduce the aerodynamic performance degradation caused by the sculling phenomenon on the flap of amphibious seaplanes, this study proposes a grid-slat fusion design method that integrates grid channels into the slats to create multiple lift surfaces. This new configuration enhances not only the lift capacity of the slats but also the lift characteristics of the main wing, leveraging ejector effects from the grid channels. A grid-slat fusion configuration parametrization method is developed based on the “new conic curve” concept, and an optimization approach is implemented using the NSGA-II algorithm. Computational fluid dynamics (CFD) verification of the 30P30N airfoil demonstrates that the grid-slat fusion design enhances the lift-to-drag ratio of the optimized 2D configuration by up to 8.5% at a specific condition, thereby significantly improving its aerodynamic performance at high angles of attack and meeting the requirements for take-off and landing. The three-dimensional configuration demonstrates a stall angle of attack delay of 2° and a maximum lift coefficient increase of 6%. Furthermore, the grid-slat composite configuration allows a better lift-to-drag ratio, and its aerodynamic characteristics improve with increasing wave height. During the wave runup phase, aerodynamic performance is further enhanced, with different wave positions significantly influencing the aerodynamic performance.

Research on Minimum Unstick Speed Flight Test Method for Civil Aircraft

The minimum unstick speed (VMU) is defined as the calibrated airspeed at which an aircraft can safely lift off and continue its takeoff without any difficulties. The VMU flight test, characterized by low-speed and high angle of attack under the influence of ground effect, poses significant challenges and high risks, making it one of the most hazardous flight test subjects in civil aircraft flight test. The research on VMU flight test methods for civil aircraft is of utmost importance in strengthening the foundation of flight test technology, improving flight test efficiency, and ensuring flight test safety.

Research on aerodynamic optimization of hypersonic missiles

Abstract To investigate the impact of different components on the aerodynamic characteristics of hypersonic missiles and missiles’optimization, a numerical simulation model of the typical hypersonic missile aerodynamic optimization was developed based on Ansys/Fluent. Based on this foundation, the missile was three-dimensionally modeled using Solidworks software. Detailed aerodynamic performance analysis was conducted on its head, tail, and canard configuration, which included key aerodynamic performance indicators such as drag coefficient and lift-drag ratio. The research findings indicate that the aerodynamic performance of the missile head design significantly affects the missile structure under investigation. Appropriate increase in the number of tail fins can effectively enhance the overall aerodynamic performance of the missile, however, if the number exceeds a certain limit, it may exert a detrimental impact on performance. In addition, at high attack angles, the use of canard configuration can significantly increase the missile’s lift coefficient and stability.

Enhancement of flying wing aerodynamics in crossflow at high angle of attack using dual synthetic jets

To address the asymmetric flow field of the flying wing under cross-flow conditions at high angles of attack, dual synthetic jet actuators (DSJAs) are positioned at the leading edge of the windward side. DSJ control effectively affects the flow separation structure on the windward side, thereby enhancing leading-edge suction. This leads to both lift enhancement and drag reduction. Furthermore, it strengthens the stabilizing roll moment and improves lateral static stability. Additionally, the effective suppression of the separation zone significantly reduces the aerodynamic load fluctuations of the flying wing after control. In terms of excitation frequency, low-frequency excitation more effectively generates lift, transfers energy downstream, promotes momentum transfer, and results in an 8.2% increase in lift. Moreover, the DSJ excitation exhibits fast response characteristics, with the entire flow establishment process taking only 190 ms. Therefore, through DSJ control, the asymmetric flow under lateral conditions can be effectively corrected, expanding the flight envelope and enhancing the maneuverability and reliability of the aircraft.

Flow Separation Control and Aeroacoustic Effects of a Leading-Edge Slat over a Wind Turbine Blade

To enable wind energy to surpass fossil fuels, the power-to-cost ratio of wind turbines must be competitive. Increasing installation capacities and wind turbine sizes indicates a strong trend toward clean energy. However, larger rotor diameters, reaching up to 170 m, introduce stability and aeroelasticity concerns and aerodynamic phenomena that cause noise disturbances. These issues hinder performance enhancement and social acceptance of wind turbines. A critical aerodynamic challenge is flow separation on the blade’s suction side, leading to a loss of lift and increased drag, ultimately stalling the blade and reducing turbine performance. Various active and passive flow control techniques have been studied to address these issues, with passive techniques offering the advantage of no external energy requirement. High-lift devices, such as leading-edge slats, are promising in improving aerodynamic performance by controlling flow separation. This study explores the geometric parameters of slats and their effects on wind turbine blades’ aerodynamic and acoustic performance. Using an adequate turbulence model at Re = 106 for angles of attack from 14° to 24°, 77 slat configurations were evaluated. Symmetric slats showed superior performance at high angles of attack, while slat chord length was inversely proportional to aerodynamic improvement. A hybrid method was employed to predict noise, revealing slat-induced modifications in eddy topology and increased low- and high-frequency noise. This study’s main contribution is correlating slat-induced aerodynamic improvements with their acoustic effects. The directivity reveals a 10–15 dB reduction induced by the slat at 1 kHz, while the slat induces higher noise at higher frequencies.

Unsteady Propeller Wake Interference on Wing in Tractor Configuration at Low-Reynolds-Number Condition

This study investigates the unsteady interaction between the propeller slipstream and NACA0012 airfoil, which causes laminar separation at a moderate angle of attack and nonlinear aerodynamic characteristics at low Reynolds numbers. The Reynolds number based on chord length was set to c, and the propeller advance ratio was set to J=0.8. Wind-tunnel experiments were conducted, including aerodynamic force measurement and time-resolved particle image velocimetry visualization. Regarding time-averaged characteristics, the propeller installed condition exhibits a linear change in lift; reduced drag; and, consequently, an improved lift-to-drag ratio. Consistent with the aerodynamic characteristics, suppressed separation and reduction in wake deficit are confirmed in the time-averaged flowfields. Additionally, vortex formation and shedding synchronized with propeller rotation are observed in unsteady flowfields at the middle and high angles of attack. This periodic and large-scale vortex structure suggests the possibility of further improving the performance of the propeller–wing system in low Reynolds numbers.

CFD Investigation of Dual Synthetic Jets on an Optimized Aerofoil's Trailing Edge

In fluid dynamics, a flow control device is used to control, manage, or modify the behavior of a fluid flow. Jet actuators work by releasing high-velocity jets of fluid, usually air or gas, into the surrounding environment to control or manipulate the flow of fluids. In this study, the flow control device, which was a dual synthetic jet actuator (DSJA), acted as a lift enhancement device over an optimized NACA 0012 aerofoil with a rounded trailing edge (TE) (Coanda surface approximately 9% of the trailing edge was modified) to enhance the lift at various angles of attack (AOAs). Fluctuating pressure inlets were introduced in two slots. When the dual synthetic jets were in control, the out-of-phase jets from the upper and lower trailing edge jets helped to boost the lift coefficient. The suction stroke from the lower half of the jet made the Coanda effect stronger in the upper half. The upper trailing edge jet deflected downwards merged with the lower one and helped to deflect the flow field closer to the bottom half. An unsteady CFD analysis was performed on optimized airfoils with and without a DSJ, with a driving frequency of 40.6 and a reduced frequency of 0.025 at a Reynolds number of 25000. The results obtained at different angles indicated that the L/D ratio was improved by 13.5% at higher angles of attack in the presence of the DSJA.

Design of Input Signal for System Identification of a Generic Fighter Configuration

This article investigates the design of time-accurate input signals in the angle-of-attack and pitch rate space to identify the aerodynamic characteristics of a generic triple-delta wing configuration at subsonic speeds. Regression models were created from the time history of signal simulations in DoD HPCMP CREATETM-AV/Kestrel software. The input signals included chirp, Schroeder, pseudorandom binary sequence (PRBS), random, and sinusoidal signals. Although similar in structure, the coefficients of these regression models were estimated based on the specific input signals. The signals covered a wide range of angle-of-attack and pitch rate space, resulting in varying regression coefficients for each signal. After creating and validating the models, they were used to predict static aerodynamic data at a wide range of angles of attack but with zero pitch rate. Next, slope coefficients and dynamic derivatives in the pitch direction were estimated from each signal. These predictions were compared with each other as well as with the ONERA wind tunnel data and some CFD calculations from the DLR TAU code provided by the NATO Science and Technology Organization research task group AVT-351. Subsequently, the models were used to predict different pitch oscillations at various mean angles of attack with given amplitudes and frequencies. Again, the model predictions were compared with wind tunnel data. Final predictions involved responses to new signals from different models. A feed-forward neural network was then used to model pressure coefficients on the upper surface of the vehicle at different spanwise sections for each signal and the validated models were used to predict pressure data at different angles of attack. Overall, the models predict similar integrated forces and moments, with the main discrepancies appearing at higher angles of attack. All models failed to predict the stall behavior observed in the measurements and CFD data. Regarding the pressure data, the PRBS signal provided the best accuracy among all the models.

Numerical simulation of cavitation flow around a wing with new tubercles design

The study investigates the benefits of adding non-uniform leading-edge tubercles to hydrofoils, drawing inspiration from the complex shaping of humpback whale flippers. The focus is on managing cavitation, a phenomenon that can affect hydrofoil performance. While previous research has mainly looked at uniform sinusoidal tubercles and their positive impact on flow dynamics and cavitation control, this study introduces a new perspective by examining the effects of non-uniform tubercles on hydrofoil performance. Advanced computational fluid dynamics (CFD) simulations using ANSYS Fluent 2024 were used to assess how these non-uniform tubercles affect the lift, drag, and cavitation characteristics of the NACA 634-021 hydrofoil. The simulations incorporated the Schnerr-Sauer cavitation model and the SST k-ω turbulence model to accurately capture the flow dynamics. The results show that non-uniform tubercles improve cavitation control by disrupting the flow in a way that delays the onset and reduces the severity of cavitation. The modified hydrofoils (non-uniform tubercles) display improved hydrodynamic performance compared to baseline designs, with significant reductions in drag and increased lift at higher angles of attack. This study provides valuable insights into the potential of mimicking natural designs to enhance flow stability and address cavitation issues, offering a significant contribution to advanced hydrofoil design in scenarios where controlling cavitation is essential. The broader implications of this research underscore the potential of mimicking natural designs to transform hydrofoil engineering and enhance flow stability in various applications.

Analysis of aerodynamic characteristics of drone wing based on CFD

In order to improve the aerodynamic characteristics of the drone wings, CFD method was used to simulate and calculate the lift coefficient, drag coefficient, and lift-drag ratio under different relative inflow velocities, as well as the velocity and pressure fields under different attack angles. Modal calculations were conducted on the wing to obtain the first four modal shapes, providing a basis for analyzing flutter characteristics. An iterative calculation method of incompressible potential flow-boundary layer based on surface element method was combined with the software XFOIL to optimize the airfoil at low wind speeds. The results indicate that the airfoil is susceptible to stall at high angles of attack, with the pressure of the separation flow being nearly equivalent to that at the separation point. Subsequent to separation, there is an increase in differential pressure resistance, resulting in a marked rise in the drag coefficient. At the optimized angle of attack, the lift-drag ratio of the optimized wing increases by 12.58 %, while there is a decrease of 0.084 % in lift coefficient and an increase of 11.21 % in drag coefficient.

Development on Unsteady Aerodynamic Modeling Technology at High Angles of Attack

Development on Unsteady Aerodynamic Modeling Technology at High Angles of Attack

Optimal Selection of Active Jet Parameters for a Ducted Tail Wing Aimed at Improving Aerodynamic Performance

The foldable tail of the box-type launch vehicle poses a risk of mechanical jamming during the launch process, which is not conducive to the smooth completion of the flight mission. The integrated nonfolding ducted tail proposed in this article can solve the problem of storing the tail in the launch box. Moreover, traditional mechanical control surfaces have been eliminated, and active jet control has been adopted to control the pitch direction of the flight attitude, which can improve the structural reliability of the tail wing. By studying the effects of parameters such as momentum coefficient, jet hole position, jet hole height, and jet angle on improving the aerodynamic performance of ducted tail wing, relatively good jet parameters are selected. Research has found that compared with jet hole height and jet angle, momentum coefficient and jet hole position are more effective in improving the aerodynamic performance of ducted tail wings. Under a trailing edge jet, a relatively good jet condition occurs when the jet hole height is equal to0.25% of the aerodynamic chord length, and the jet angle is equal to 0°. At this time, with the increase of the jet momentum coefficient, the effect of increasing the lift of the ducted tail wing is the best. Finally, a comparative analysis is conducted on the lift and drag characteristics between the ducted tail wing and traditional tail wing, and it is found that the ducted tail wing can generate lift at a 0° attack angle and will not stall in the high attack angle range of 12°~22°, with broad application prospects.

Research on assisted recovery algorithm of stall state based on signal guidance

Abstract Given the lack of quantitative guidance in the current stall recovery process, which leads to the pilot’s misoperation or untimely recovery, referring to the energy control theory of complex state recovery, a stall state-assisted recovery algorithm based on pitch angle, engine thrust, and roll angle signal guidance was determined. The structure pilot model and the kinematics simulation model of aircraft at a high angle of attack were established. The effectiveness of the algorithm has been verified by simulation analysis. The man-machine closed-loop simulation analysis results show that the algorithm can guide the pilot in effectively recovering from stall conditions under different stall scenarios and engine failure conditions.

Proper orthogonal decomposition analysis for two-dimensional wake transition behind a NACA 0012 airfoil in a soap film

Abstract An experimental study has been conducted to analyze the flow characteristics around a NACA 0012 airfoil in a horizontal soap film tunnel. The investigation involves both the qualitative observations and the quantitative measurements at various angles of attack (0° to 20°) for Reynolds numbers ∼ 3000 and 5000. Flow visualizations were carried out using the interference technique, while particle image velocimetry (PIV) was used for velocity field measurements. The study examines the two-dimensional wake transition of the NACA 0012 airfoil under different Reynolds numbers and angles of attack in a soap film tunnel. Results indicate that changes in the trailing flow within the soap film are primarily influenced by the Reynolds number and angle of attack. The visualization of the flow exposes different states of wakes and their corresponding flow structures. At lower angles of attack α ≤ 6°, vortex shedding occurs in an alternating mode, while at intermediate angles (8° to 16°), the wake widens. The vortices exhibit more chaotic and turbulent behavior at higher angles of attack, i.e., α ≥ 16°. Furthermore, the study indicates that the same wake transition takes place at lower angles of attack as Reynolds numbers rise.

Omnidirectional control of the wake of a circular cylinder with spinning rods subject to a turbulent flow

We numerically investigate the attribute of omnidirectionality of the flow-control system comprised of a large circular cylinder equipped with eight spinning rods of smaller diameter, subject to an incoming flow that adopts different angles of attack. Detached-eddy simulations are employed to compute hydrodynamic loads and to provide flow topology at a Reynolds number of 1000. Two cases are assessed regarding the rods angular velocities. In case 0, all rods spun with the same angular velocity. In case 1, velocities were inspired by potential-flow theory. The two systems have the same input kinetic energy in common. To assess the system response, the velocities were increased proportionally. Both cases succeeded in reducing the mean drag. However, while case 1 proved to become ever “more omnidirectional” with increasing angular velocities, case 0 demonstrated to be prone to the angle of attack as it was unable to suppress vortex shedding for sufficiently large slopes of the incoming flow, and in such circumstances, unable to reduce hydrodynamic forces. We verify that the lift is mitigated in case 1, in contrast to case 0. Even for a vortex-free downstream flow resulting from configurations of high velocities and high angle of attack, the latter produces asymmetric recirculation regions downstream of the system that drive a pressure imbalance. The different outcomes of the two systems are also explored from the viewpoint of power consumption, and it is revealed that the omnidirectionality of case 1 is intrinsically related to the emphasis imposed on rotation rates of a subset of the eight rods.

Design perspectives of a system identification approach of the NATO AVT-316 multi-swept wing aerodynamics

Air supremacy requires enhanced maneuvering capabilities at high angles of attack and even beyond the stall angle. High angle-of-attack (high-α) maneuverability can be achieved using swept wings and tailored leading-edge shapes to replace local and disorganized flow separation with controlled separation-induced leading-edge vortices (LEV). Strong leading-edge vortices delay the stall to higher angles and generate a non-linear lift increment up to the angle of attack where the jet-type flow structure of LEV changes to a reversed-flow bubble (vortex breakdown phenomenon). A multi-swept wing configuration has the potential to delay the vortex breakdown to even higher angles as the vortices formed over the front wing can energize vortices formed over the main wing and lead to vortex merging. This article is focused on understanding the unsteady interactions between multiple leading edge vortices formed over multi-swept wing configurations in the subsonic speed regime. Specifically, this article investigates the aerodynamic characteristics of wings being evaluated under the initiative of the NATO STO AVT-316 Task Group. Highly refined meshes, and the use of hybrid turbulence models such as Detached Eddy Simulations (DES) and Delayed DES are required to accurately resolve the vortical flows over these wings. Simulating all flow conditions of interest is a computationally expensive approach. A system identification method was therefore proposed to rapidly and accurately generate aerodynamic models of these wings. The method uses a novel piece-wise chirp (constant amplitude and increasing frequency) motion as an input signal (training maneuver). The motion computational cost is equivalent to the cost of six static CFD simulations, however it can predict aerodynamic responses of the wings over a wide range of angles of attack. The method has been tested for double and triple delta wings. Some design considerations are provided based on predicted flow features and aerodynamic data. Prediction results with different turbulence models, sting geometries, grid resolutions and an adaptive mesh refinement approach are provided.

Aerodynamic Analysis and Simulation for a Z-Shaped Folding Wing UAV

The potential of folding wing unmanned aerial vehicles (UAVs) in enhancing the adaptability of complex missions is substantial. Analyzing the aerodynamic characteristics of these UAVs is vital for optimizing the design of their folding wing configuration and airfoil shape. In this study, a model of a Z-shaped folding wing UAV was established with the objective of enhancing UAV maneuverability. An integrated vortex lattice method (VLM) was employed to analyze the aerodynamic characteristics of the Z-shaped folding wing and numerical simulations were utilized to validate the obtained results, which prove the effectiveness of the integrated VLM in studying aerodynamic characteristics at a high angle of attack of the Z-shaped folding wing UAV. This is a new way to reduce computation time while maintaining accuracy to calculate such complex folding structures in high fidelity. Furthermore, the Z-shaped folding wing configuration demonstrates enhanced maneuverability at high angles of attack, and a Simulink flight simulation model based on the aerodynamic coefficients of the Z-shaped folding wing verifies this property. This analysis can properly predict the post-stall characteristics for the Z-shaped folding wing UAV to ensure the safety of the vehicle during flight.