Angle Of Attack Research Articles

Endoscopic Endonasal Approach to the Inferolateral Intraconal Orbit: An Anatomical Analysis of Exposure and Maneuverability.

Endoscopic endonasal techniques, initially developed for sinonasal tumor resection, have revolutionized the approach to orbital lesions. The emergence of endonasal orbital tumor surgery has prompted anatomical studies focusing on the medial orbit, yet there remains a lack of literature on maneuverability lateral to the optic nerve (ON), with current feasibility assessments relying primarily on the plane of resectability (POR). Bilateral anatomical dissections were conducted on four latex-injected human cadaveric heads using an endoscopic medial and inferior orbitotomy and superomedial displacement of the inferior rectus muscle (IRM) to access the inferolateral intraconal quadrant. Measurements of distances, areas, angles of attack, and volumetric exposure were obtained using stereotactic points from an imaging-based navigation system. Additionally, an illustrative case was presented to demonstrate the endoscopic management of laterally based intraconal lesions. The intraconal space was safely accessed through superomedial displacement of the IRM. The mean intraconal volumetric exposure attained through this maneuver was 2.78cm3 (1.18cm3). The most superolateral point reachable by the ipsilateral endoscopic endonasal approach was consistently lateral and superior to the ON at a mean absolute distance of 1.45cm (0.37cm). Maneuverability at this target point was superior in the sagittal plane, noted by a larger vertical angle of attack compared with the horizontal angle of attack. This study demonstrates that inferolateral intraconal dissection through an ipsilateral endoscopic endonasal approach is feasible via a medial orbitotomy and superomedial retraction of the IRM. Additionally, our findings reaffirm lesions below the POR are suitable for endoscopic endonasal resection.

Intelligent aerodynamic modelling method for steady/unsteady flow fields of airfoils driven by flow field images based on modified U-Net neural network

An intelligent modelling method driven by flow field images for predicting steady and unsteady flow filed around aerofoils has been developed. Signed Distance Field (SDF) images achieve dimensionality enhancement of aerofoil geometric information, and ‘synthesised images’ achieve dimensionality enhancement of the angle of attack of the aerofoil and Mach number. An intelligent aerodynamic model for steady flow field of aerofoils is constructed based on the U-Net neural network architecture, and further incorporating a long short-term memory (LSTM) module to construct a U-Net-LSTM neural network architecture to extract the temporal features. Typical NACA aerofoils results show that, the prediction error for steady flow is less than 1.98%, while the prediction error for unsteady flow is less than 2.56%. Additionally, the model demonstrates good generalization capability, with a generalization error for steady flow less than 2.45% and a generalization error for unsteady flow less than 3.34%. This research provides a new method for intelligent aerodynamic modelling based on physical representations. Compared to existing methods, this method avoids the need for extracting aerofoil geometry information and eliminates the necessity of predicting the flow field point by point, making it more concise and efficient. Highlights 1. An aerodynamic model was constructed using U-Net to rapidly predict the steady flow field around airfoils. 2. A Long Short-Term Memory (LSTM) module was incorporated to capture temporal information, enabling the rapid prediction of the unsteady flow field around airfoils. To address the problem of ‘dimension loss’ in the modelling datasets, effective data dimensionality enhancement was achieved using SDF images and ‘synthesized images’.

Numerical Study on the Hydrodynamics of Fish Swimming with Different Morphologies in Oblique Flow

In confined and intricate aquatic environments, fish frequently encounter the need to propel themselves under oblique flow conditions. This study employs a self-developed ghost-cell immersed boundary method coupled with GPU acceleration technology to numerically simulate the propulsion dynamics of flexible biomimetic fish swimming in oblique flow environments. This research scrutinizes diverse biomimetic fish fin morphologies, with particular emphasis on variations in the Strouhal number and angle of attack, to elucidate hydrodynamic performance and wake evolution. The results demonstrate that as the fin thickness increases, the propulsion efficiency decreases within the Strouhal number range of St = 0.2, 0.4. Conversely, within the range of St = 0.6 to 1.0, the efficiency variations stabilize. For all three fin morphologies, an increase in the Strouhal number significantly augmented both the lift-to-drag ratio and thrust, concomitant with a transition in the wake structure from smaller vortices to a larger alternating vortex shedding pattern. Furthermore, within the Strouhal number range of St = 0.2 to 0.4, the propulsion efficiency exhibits an increase, whereas in the range of St = 0.6 to 1.0, the propulsion efficiency stabilizes. As the angle of attack increases, the drag coefficient increases significantly, while the lift coefficient exhibits a diminishing rate of increase. An increased fin thickness adversely affects the hydrodynamic performance. However, this effect attenuates at higher Strouhal numbers. Conversely, variations in the angle of attack manifest a more pronounced effect on hydrodynamic performance. A thorough investigation and implementation of the hydrodynamic mechanisms demonstrated by swimming fish in complex flow environments enables the development of bio-inspired propulsion systems that not only accurately replicate natural swimming patterns, but also achieve superior locomotion performance and robust environmental adaptability.

Experimental Aerodynamics of a NACA 4424 Airfoil at Low Reynolds Number Flow

This paper presents wind tunnel data on the aerodynamic characteristics of a NACA4424 airfoil operating under low Reynolds number flow conditions (∼ Re = 2 × 105). The study investigates the lift, drag, and stall behavior of the airfoil, which are critical for applications in engineering such as small unmanned aerial vehicles (UAVs) and micro air vehicles (MAVs). Experimental data were collected through wind tunnel testing across various angles of attack at a fixed Reynolds number.To provide further insight, the experimental results are complemented by XFOIL simulations, which illustrate the impact of low Reynolds number conditions on aerodynamic performance. These findings enhance the understanding of airfoil behavior in low Reynolds number regimes and support the design and optimization of efficient airfoil profiles for small-scale aerial systems.

The Impact of Camber Variation on NACA 2412 Airfoil Efficiency and Its Implications for Adaptive Engineering Solutions

This paper investigates the effects of varying the camber on the aerodynamic efficiency of the NACA 2412 airfoil by analyzing the Lift-to-Drag (L/D) ratio. Using wind tunnel tests at a constant speed of 95 MPH, data was collected for different camber configurations, and L/D ratios were computed for each trial. The NACA 2412 airfoil camber was modified to increase the camber by 20%, decrease it by 20%, and decrease surface area by 20%. These were all tested at Angle of Attack values from 0 to 30 in 5-degree increments. The results revealed a strong correlation between camber variation and aerodynamic efficiency, with certain camber settings significantly enhancing performance at specific Angles of Attack. While the original NACA 2412 served as a control, modifications such as reduced camber and surface area demonstrated significant efficiency changes, underscoring the role of camber in optimizing performance. The study provides valuable insights for optimizing airfoil design, offering practical applications in aircraft engineering, particularly in the development of systems that can adapt wing geometry dynamically to optimize performance. However, limitations such as fixed airspeed and limited camber variations were noted, highlighting the need for further investigation into more diverse conditions. These findings contribute to a broader understanding of how engineering solutions can enhance aircraft performance by incorporating adaptable design elements.

Effects of variable blowouts on aerodynamic loss reduction performance of compressor bionic blades

Abstract A passive flow control method, inspired by blowouts, is employed to eliminate flow separation and reduced losses associated with higher compressor loads. By implementing bionic-blowout variant dimples on the blade suction surface, the flow characteristics of the dimple-shaped cascade were investigated. The loss generation mechanism was also analysed. Firstly, the reliability of the numerical method was confirmed through experimental validation. Subsequently, biomimetic principles were applied to arrange dimples on the suction surface of the cascade blades, and the effects of various blowouts were analysed The result revealed that vortices within the dimples induce external fluid into the dimples, enhancing the turbulent kinetic energy of the external fluid and improving wall-adjacent flow adherence. The bionic-blowout variant dimples creates a "rolling bearing" effect that reduces frictional losses, which control flow separation. Within a certain blowout range, the bionic-blowout variant dimples significantly improve the flow conditions. At -6° angle of attack, the total pressure loss of the dimple-structured cascade decreased by 35.85%, and the pressure ratio increased by 2.35%. The bionic-blowout variant dimples on the blade suction surface exhibit a three-dimensional disturbance effect. The induced vortex structures regulates the boundary layer transition and suppress the formation of laminar separation bubbles, effectively improving the flow conditions near the corner region.

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 water flow characteristics and stress around bridges during floods

ABSTRACT Due to the frequent threat of floods to structures and engineering constructions near rivers, this study examines the impact characteristics of river hydrodynamics on structures under excessive flow during floods, using Jiefang Bridge as an example. We employ the fluid volume two-phase flow model (volume of fluid) in computational fluid dynamics, combined with advanced geometric reconstruction techniques such as the isoAdvector method, to simulate the dynamic changes of the gas–liquid interface in the river. On the premise of ensuring grid independence, high-precision structural grids were used to finely divide the study area and numerical simulations were conducted. The research results indicate that when a flood contacts a bridge, the force on the bridge rapidly increases and fluctuates, reaching a significant peak of over 6,000,000 N. Bridge piers have a significant hindering effect on floods and their impact gradually expands over time. Vorticity and turbulence energy analysis indicate the presence of strong flow disturbances around the bridge pier. In addition, the characteristics of the contact surface between water flow and bridges also significantly affect the stress and flow characteristics of bridges. Especially at a 45° angle of attack, the force on the bridge decreases, but the wake velocity increases.

Angle of Attack Effects on the Induced Structural Loads of a Weapons Bay

AbstractAero-acoustic analysis was conducted on a weapons bay numerical model with doors, incorporating radar cross section reduction features. The effect of the angle of attack on the aero-acoustic response of the cavity was analysed at Mach numbers of 0.85 and 1.20. It was found that incidence influenced both mean-flow features and acoustic response. Further, linear and angular accelerations induced by the flow on the bay doors revealed potential adverse fluid–structure coupling when the results were compared with modal analysis. Again, the angle of attack did influence the aeroacoustic effects on the cavity door structure.

The Effect of Formal Specifications and Working Conditions on the Resistance and Vibration of the NACA 4415 Aircraft Wing Model

Due to their role in airplane performance, wings receive much attention considering their strength enhancement and vibration reduction. Many parameters have been considered and various materials have been used to achieve these objectives. The current work studies numerically the effect of the number of ribs and the angle of attack, on strength, response, and natural frequency at various speed values, using the ANSYS 2021 R1 solver. The adopting material is the AA 7075 T6 aluminum alloy with 71.7 GPa modulus of elasticity, 503 MPa tensile yield strength, 2810 kg/m3 density, and 0.33 Poisson’s ratio. Results show that when the velocity is increased by 30%, a corresponding elevation of 11% can be seen in vibrational distortion. Regarding the angle of attack, it was noted that doubling its value leads to a 28% reduction in vibration-induced deformation. This phenomenon occurs as a result of the alteration in the pressure distribution on the wing caused by the change in the angle of attack.

Effects of cavitation number and pitching frequency on hysteresis characteristics of a pitching hydrofoil

In this study, the effect of cavitation number σ and pitching frequency f* on hysteresis characteristics of a pitching hydrofoil, has been investigated. The angle of attack α changed from 5° to 15°, then from 15° to 5° at each pitching period. A pitching 2D(Two-dimensional) Clark-y hydrofoil is analyzed with high-speed video recording for the cavitation pattern. The hysteresis phenomenon is observed in increasing and decreasing of α, and the hysteresis effects changed with σ and f*. The cavitating flow around the pitching hydrofoil during different conditions are simulated by revised k-ω SST(Shear Stress Transfer) turbulence model and Merkle cavitation model. The calculation results of hysteresis characteristic parameters showed that the decrease of σ leads to the increase of hysteresis effect. As σ decreased, the evolution of cavity vortex is more complex. Especially in the downstroke, there are complex phenomena such as vortex decomposition and merging, which leads to the intensification of hydrodynamic hysteresis effect. There is a nonlinear relationship between the hysteresis characteristic parameters and f*. As f* increases, its influence on the cavitation flow in the downstroke becomes more and more serious. Besides, the evolution form of cavitation vortices also changes, which leads to the change of hysteresis characteristics.

Aerodynamic interaction mechanisms in typical wingtip-mounted tractor propeller configurations

The wingtip-mounted tractor propeller configuration has been extensively studied due to its great potential for improving wing aerodynamic performance. In the present work, the aerodynamic interaction mechanisms in typical wingtip-mounted tractor propeller configurations are analyzed in depth using the reformulated vortex particle method. The results show that the elliptical lift distribution over the entire wing is altered by the installation of the tip-mounted propeller. The lift coefficient increases with inboard-up rotation and decreases with outboard-up rotation. Three key aerodynamic interaction mechanisms, swirl recovery, slipstream distortion, and slipstream impingement, are investigated. The swirl recovery mechanism generated by the inboard-up rotating propeller positively contributes to the performance of downstream wing. For the outboard-up rotation, the propeller-induced downwash results in reduced lift and increased induced drag. The interaction between the propeller-induced spanwise velocity and the wingtip-induced crossflow results in slipstream distortion. At α = 0°, for either inboard-up or outboard-up rotation, the slipstream on the retreating side is moved toward the propeller axis and away from the propeller axis on the advancing side. With the change of the rotation direction and angle of attack, the slipstream geometry exhibits different features. The slipstream impingement induced by the propeller generates time-varying loads on the downstream wing at the blade passing frequency. The propeller-induced tip vortices start to bend close to the leading edge and their vorticity increases, and then the vortex tube begins to deform. A higher angle of attack results in larger fluctuations in the downstream wing's drag coefficient.

Experimental study of flow-induced vibration in a two degrees-of-freedom flexibly mounted triangular prism in crossflow

This study experimentally investigates the flow-induced vibration (FIV) of a flexibly mounted triangular prism with two degrees of freedom (DoF), capable of oscillating in its first two vibrational modes in the crossflow direction. The experiments were conducted by varying the angle of attack (α) in the range of 0°–60° and eigenfrequency ratio (R), which is the ratio between the second and first eigenfrequency, from R = 1.5 to 3. For α = 0° and 15°, no significant oscillations were observed. At α=30°, both vortex-induced vibration (VIV) and galloping-type response were detected. For higher angles of attack, α = 45° and 60°, a pure galloping type response was identified. Hydrogen bubble flow visualization was employed to analyze the vortex-dominated wake and to discern the nature of the FIV response—whether it was VIV or galloping. Although the prism was free to oscillate in both its first and second modes, only the first mode contributed to the FIV response at α = 45° and 60°, where galloping was dominant. The FIV response remained primarily influenced by the first mode, except when mode two was externally excited, resulting in pronounced hard mode-two galloping behavior. Because mode one predominantly drives the system's overall FIV response, variations in the eigenfrequency ratio had minimal impact on the system's overall FIV behavior.

On the mechanism of frequency lock-in vibration of airfoils during pre-stall conditions

Potential frequency lock-in vibration can frequently occur in aircraft flying at separated flow conditions during take-off and landing stages, severely threatening the safety of the aircraft. A deeper understanding of the lock-in phenomenon in pre-stall (steady separated flow) conditions is necessary to improve aircraft reliability and safety. In this paper, a reduced-order model (ROM) for the pitching NACA0012 airfoil in steady separated flow is established. A linear aeroelastic model is then obtained by coupling the ROM with the structural dynamical equation with the pitching degree of freedom, and it is verified by the computational fluid dynamics/computational structural dynamics (CFD/CSD) simulation. Next, the mechanism of frequency lock-in vibration is revealed by the ROM-based aeroelastic model of different structural natural frequencies. Results from the complex eigenvalue analysis indicate that the instability can be divided into two patterns. At high frequencies, the flutter frequency locked onto the natural frequency of the structure, and it is dominated by the instability of structural mode. At low frequencies, the flutter frequency follows the fluid characteristic frequency, which is dominated by the instability of the fluid mode. Finally, the effects of the angle of attack and mass ratio are investigated. The damping of dominant fluid mode decreases with the increase of angle of attack, which affects the structural mode through coupling effects. Therefore, the angle of attack influences the upper boundary of the coupling system’s instability (high frequency boundary). On the contrary, the mass ratio mainly influences the lower boundary of instability (low frequency boundary), because fluid mode becomes unstable at low frequencies merely when the mass ratio is relatively low.

Critical Assessment of Quadratic Closures for Prediction of Corner Flow Separation

The work proposed in this paper aims at improving the physical understanding and modeling of junction flows by conducting an analysis of several quadratic constitutive relations (QCRs) applied to corner vortices. Reynolds-averaged Navier–Stokes computations are performed on two academic configurations for verification purposes and on a technical application of wing–body juncture featuring corner flows to achieve a better comprehension of the QCR variants’ ability to reproduce turbulent stress combinations relevant to secondary flows generation. This addresses the more theoretical interest of analyzing the onset of corner separation (at an angle of attack α=11 deg) and the role of corner flow vortices. Linear eddy viscosity model and the extended QCR failed to detect these vortical structures; the latter encountered numerical stability difficulties. On the other hand, QCR2000, QCR2020, and QCR(r) showed behavior consistent with a simulation using the Reynolds Stress Model, experiments, and literature results. This better prediction was found to be related to the ability of these models to accurately predict the stress-induced vortex that acts in delaying and reducing the size of the corner separation. Notably, the more recent QCR(r) and QCR2020 have enhanced the estimation of the normal stress combination v′2¯−w′2¯ compared to the more widespread QCR2000, demonstrating their validity as alternative models.

Advancing graph neural network architecture for fluid flow and heat transfer surrogate modeling: Variable boundary conditions and geometry

Graph neural networks (GNNs) represent a promising instrument for surrogate modeling, capable of handling unstructured computational meshes naturally. We address a typical issue of the accuracy degradation for larger computational domains due to the limited receptive field of GNN models and long-range global interactions between nodes of the mesh. We propose a modification of the GNN architecture allowing to improve the accuracy by a factor of 3 without significant increase in computational costs. The validation tests of the model concentrate on the two-dimensional stationary fluid flow around a bluff body in a channel and corresponding heat transfer. The problem formulation includes bluff bodies of randomly generated shapes and various boundary conditions. The model shows a robust performance for the out-of-domain data, i.e., the flow over an airfoil for different angles of attack.

Numerical analysis of flow-induced vibrations and heat transfer in a triangular arrangement of circular cylinders

This numerical study explores the flow characteristics and heat transfer performance of three isothermal circular cylinders arranged in a triangular configuration at angles of attack of 45° and 60°. The impact of one-degree-of-freedom (1DOF) flow-induced vibrations (FIV) in the cross-flow direction on forced convective heat transfer is analyzed using ANSYS FLUENT, considering reduced velocities from 4 to 8 at a constant Reynolds number of 100. Comparative simulations are conducted for both stationary and vibrating cylinders. Results indicate that, when stationary, the cylinders at a 45° angle exhibit lower heat transfer rates compared to those at 60°, with a 2.66% reduction in overall heat transfer. The study also examines the nuanced effects of 1DOF FIV in the cross-flow direction on heat transfer: while the upstream cylinder generally experiences increased heat transfer during vibrations, the downstream cylinders often show reduced rates. Specifically, at a 45° angle, the most significant reduction in heat transfer from downstream cylinders, nearly 9.99%, occurs at reduced velocities of 5 and 6. For the stationary tube bundle at 45°, the average Nusselt number is 11.77, but it decreases by approximately 5.21% at a reduced velocity of 5 under vibration. Conversely, at a 60° angle, the average Nusselt number generally increases at higher reduced velocities, except at Ur = 4, where it drops by 2.89% from the stationary state. These findings highlight the complex interplay between 1DOF vibration and heat transfer in triangular cylinder arrangements.

Experimental investigation of the flow disturbance near the trailing edge of slotted and non-slotted blades using skewness and kurtosis

The present study conducts an experimental investigation into the flow characteristics over a cascade of both slotted and non-slotted compressor blades. The focus is on evaluating potential statistical correlations between higher-order moments of velocity fluctuations, including Skewness and Kurtosis. The linear axial cascade comprises three NACA6409 blades, which are tested in both normal and slotted blade. Data acquisition was conducted using a hot wire anemometer at three measurement stations within the cascade. The hot wire sensor was positioned at distances of x/c = 0.125, 0.25, and 0.5 from the trailing edge (x), where x represents the distance from the probe to the trailing edge of the airfoil and (c) is the chord length of the blade. Measurements were taken at a blade angle of attack of 0° and two Reynolds numbers: 22,750 and 45,500. Results indicate that blade grooving enhances flow velocity, postpones separation and improves flow control in the trailing edge region. By comparing calculated Skewness and Kurtosis values with those predicted by existing boundary layer and free jet relations, more consistent correlations were identified. To provide more accurate relationships, two polynomials of the second and third order have been used. It was found that high-order values of velocity were obtained more accurately with the relations presented in this research. Although the accuracy of these predictions is significantly reduced in the proportion of larger distances. In distant stations, the loss velocity has decreased. As the distance from the model increases, the amount of inhomogeneities in the sequence increases and the values of the opposite Skewness become zero. Turbulence intensity has been reduced by slotting the blades.

Experimental Investigation of Aerodynamic Noise Characteristics of Tandem Asymmetric Airfoils Across Varied Angles of Attack

Experimental Investigation of Aerodynamic Noise Characteristics of Tandem Asymmetric Airfoils Across Varied Angles of Attack

Empirical formulas of the flutter critical wind speed for cable-suspended bridges under various wind angles of attack

Empirical formulas of the flutter critical wind speed for cable-suspended bridges under various wind angles of attack