Angle Of Attack Research Articles

Aerodynamic Characteristics and Dynamic Stability of Coning Motion of Spinning Finned Projectile in Supersonic Conditions

For a spinning projectile, coning motion induced by disturbances during flight can have a unique impact on the lateral force and yawing moment, which may further affect flight stability and maneuverability. The flow over a coupled spinning–coning projectile and a spinning projectile was numerically simulated by solving the unsteady Reynolds-averaged Navier–Stokes (URANS) equation with an implicit dual-time stepping method and a spinning–coning coupled motion model established through a dynamic mesh technique. The variation in transient and time-averaged aerodynamic characteristics with the angle of attack (AoA), dimensionless spin rate, and dimensionless cone rate was analyzed, and the specific effect of coning motion on the lateral force and yawing moment was revealed. Based on these findings, the yawing moment term in traditional angular motion theory was modified, and the flight response to the initial disturbance was discussed. The results indicate that the time-averaged lateral force and yawing moment of the spinning–coning coupled projectile are multiplied compared with those of the spinning projectile and vary linearly with the dimensionless spin rate and cone rate. The main factors affecting the lateral force are the coning motion-induced effective angle of sideslip (AoS), asymmetric expansion waves, and asymmetric vortices. The much larger yawing moment induced by spinning–coning coupled motion can more easily cause AoA divergence and flight instability.

Dynamic analysis of cross brace anti-warp stiffness performance for heavy haul freight wagon

A dynamic model was developed to assess the impact of cross braces on the lateral stability and curve navigability of heavy haul freight wagons. Simulations evaluated the dynamic performance of empty and loaded wagons under varying cross-brace anti-warp stiffness. The study focused on stability, ride quality during straight-line travel and safety indices across different curve radii. The results show that cross braces significantly enhance vehicle nonlinear critical speed. In straight-line sections, variations in anti-warp stiffness have a minimal impact on vertical ride quality but improve lateral ride quality. In curved sections, stiffness changes have little impact on derailment coefficient, wheel load reduction rate and attack angle but notably affect wheelset lateral force and wear index. Safety and ride quality indices decrease with increasing vehicle speed, while the impact on vertical indices remains minimal. As the curve radius increases, safety indices decrease. Significant changes in attack angle and derailment coefficient are observed when the curve radius shifts from R400 to R600. The study confirms that larger bolt preloads increase anti-warp stiffness while larger mounting angles decrease it. Selecting the appropriate bolt preload and cross-brace angle is crucial for optimising performance and safety in vehicle engineering applications.

Aerodynamic coefficient models for disk-shaped biomass particles with low aspect ratios

In numerical simulations of biomass co-firing in coal-fired power plant boilers, the current literature lacks precise models for the drag, lift, and torque coefficients of non-spherical particles. To address this gap, this study develops a novel set of aerodynamic coefficient correlations specifically for disk-shaped biomass particles across varying aspect ratios (0<Ar < 1), Reynolds numbers (1≤Re ≤ 2000), and angles of attack (0°≤θ ≤ 90°). Using the body-fitted mesh method in OpenFOAM, combined with direct numerical simulation and theoretical analysis, this study reveals the critical roles of aspect ratio, Reynolds number, and angle of attack in determining the flow behavior and force characteristics of disk particles. A comprehensive parametric analysis demonstrates these dependencies. Numerical validation confirms that the proposed correlation models maintain high accuracy across different flow parameters, with low mean square errors (8.48 × 10−2, 2.5 × 10−2 and 8.1 × 10−3 for drag, lift, and torque, respectively) and low average relative errors (1.37%, 3.21%, and 1.89%). Furthermore, a comparative analysis with experimental and simulated data from existing literature shows excellent agreement, with relative errors below 5% for conditions up to Re ≤ 300. This correlation model significantly improves the simulation accuracy of non-spherical biomass particles in multiphase flow systems, providing a robust foundation for fluid dynamics optimization in industrial applications such as coal-fired boilers and biomass co-firing systems.

Hydrofoil Installation and Performance Optimisation for Ship Resistance Reduction in Trimaran Through Particle Swarm Optimisation Method

Abstract The trimaran vessel performs well both in calm waters and in waves. To improve its hydrodynamic efficiency, a hydrofoil is installed at the rear part of the trimaran. The primary aim of this hydrofoil is to reduce the overall resistance while the ship is moving. This study focuses on minimising the ship’s total resistance. An optimisation process is designed to determine the best position and angle of attack (AoA) for the hydrofoil at the design speed. To achieve this, a multi-disciplinary optimisation (MDO) platform is employed to conduct a computation fluid dynamics (CFD)-based automated design study. The optimisation method integrates STAR-CCM+ software with the particle swarm optimisation (PSO) algorithm as the optimiser. The flow field and wave patterns around the trimaran are analysed to assess resistance improvements. The results reveal that the optimal position for the NACA6612 hydrofoil is towards the stern and away from the midship, with the ideal AoA being 5.19 degrees at cruising speed. Comparisons indicate that the resistance of the trimaran with the optimised hydrofoil is reduced by approximately 4.49% compared to a trimaran without the hydrofoil.

NACA0012 airfoil at Reynolds numbers between 50,000 and 140,000 — Part 1: Steady freestream

NACA0012 airfoil at Reynolds numbers between 50,000 and 140,000 — Part 1: Steady freestream

A New Concept for Cervical Expansion Screws Using Shape Memory Alloy: A Feasibility Study.

In general, sufficient anchoring of screws in the bone material ensures the intended primary stability. Shape memory materials offer the option of using temperature-associated deformation energy in a targeted manner to compensate the special situation of osteoporotic bones or the potential lack of anchoring. An expansion screw was developed for these purposes. Using finite element analysis (FEA), the variability of screw configuration and actuator was assessed from shape memory. In particular, the dimensioning of the screw slot, the actuator length, and the actuator diameter as well as the angle of attack in relation to the intended force development were considered. As a result of the FEA, a special configuration of expansion screw and shape memory element could be found. Accordingly, with an optimal screw diameter of 4 mm, an actuator diameter of 0.8 mm, a screw slot of 7.8 mm in length, and an angle of attack of 25 degrees, the best compromise between individual components and high efficiency in favor of maximum strength can be predicted. Shape memory material offers the possibility of using completely new forms of power development. By skillfully modifying the mechanical and shape memory elements, their interaction results in a calculated development of force in favor of a high primary stability of the screw material used. Activation by means of body temperature is a very elegant way of initializing the intended locking and screw strength.

Triangular and semi-circular serrations in raked winglets: Numerical analysis of vortex dynamics and drag control

The present study explores the aerodynamic performance of serrated raked winglets (SRWs) through detailed computational fluid dynamics analysis, focusing on drag reduction, lift enhancement, and overall efficiency improvements. Utilizing the National Advisory Committee for Aeronautics (NACA) 653218 airfoil, simulations were conducted across a range of angle of attack using a realizable k–ε turbulence model. The study investigates the impact of key parameters, such as serration geometry, count, and spanwise placement on the aerodynamic characteristics. Results reveal that SRWs outperform conventional and raked winglet designs, achieving up to a 14.5% improvement in the lift-to-drag ratio (L/D) at higher angles of attack, with a 15% reduction in drag compared to a conventional wing. The incorporation of serrations was found to effectively minimize wingtip vortex intensity and turbulence, contributing to enhanced flow stability and reduced energy losses. A comparative analysis of triangular and semi-circular serrations highlights the superior vortex suppression capabilities of triangular designs, particularly when positioned near the wingtip, leading to a 6% higher L/D ratio than semi-circular configurations. These findings underscore the potential of SRWs as a transformative wingtip device for optimizing aircraft aerodynamic performance and fuel efficiency, offering valuable insight for future experimental and computational studies in advanced winglet design.

Flow Analysis of Hammerhead Launcher Geometries in the Transonic Regime

Hammerhead launcher configurations, characterized by a larger diameter in the payload fairing than the rest of the launch vehicle, face substantial challenges during transonic operations due to their susceptibility to flow separation. This experimental study investigates the influence of the nose and boat tail geometry on the flow around hammerhead configurations in the transonic regime (Ma=0.7–0.8) and for various angles of attack (α=0–4°). To gain a general understanding of the shockwave structures, flow separation and reattachment, oil flow and schlieren visualizations were employed. Schlieren visualizations were also utilized to characterize the level of unsteadiness in these regions. Additionally, particle image velocimetry was employed to quantify variations in the velocity field. The study’s findings reveal an optimization of flow performance in the presence of a bi-conic nose, attributed to the creation of two-shockwave structures with relatively low intensity. This is in contrast to the ogive and conic noses, which exhibit a single, more detrimental shockwave structure. The investigation into different boat tail angles indicates that adopting low-angle boat tails (5° and 15° compared to 34°) leads to a noticeable reduction in the separated area, albeit associated with an increase in the range of oscillation of the shockwave structures.

Aerodynamics of High-Bypass-Ratio Aeroengine Nacelles: Numerical and Experimental Investigation

This work presents a numerical and experimental investigation of the nacelle aerodynamics for high-bypass- ratio aeroengines. A conventional nacelle that is representative of a current standard, and a compact design that is envisaged for future aeroengines, were optimized with an existing computational method. Both nacelles were tested in a large-scale transonic wind tunnel. For the first time, the aerodynamic benefits of compact nacelles are demonstrated through an experimental test campaign. Measurements and computational fluid dynamics (CFD) simulations confirmed the drag reduction of compact configurations across a wide range of operating points with different flight Mach numbers, mass-flow capture ratios, and angles of attack. For midcruise conditions with a Mach number of 0.85, this was a drag reduction of 8.5% and 8.8% for the measurements and CFD, respectively. These benefits are similar to an isolated optimization, that is, not installed in the wind tunnel, which confirmed the capabilities of the method to identify the drag benefit of compact designs. Relative to the measurements, the main aerodynamic characteristics on the nacelles were captured by CFD in terms of isentropic Mach number distributions and shock location. This work provides a quantitative evaluation for the use of CFD within an industrial setting for nacelle design and analysis.

Natural convection of water/Titanium oxide nanofluid inside a closed Enclosure at different angles of attack

Natural convection of water/Titanium oxide nanofluid inside a closed Enclosure at different angles of attack

A novel variable pitch control strategy to improve the aerodynamics of vertical axis wind turbine

The low efficiency and complex aerodynamic characteristics of vertical-axis wind turbines (VAWTs) have limited their industrial development and application. An active variable pitch method can improve the aerodynamic performance of VAWTs, and different pitch control strategies yield varying improvements. In this study, a novel pitch control strategy for constant blade angle of attack (AoA) has been proposed to improve the aerodynamic performance of Darrieus H-type VAWTs. Numerical simulations have been performed to investigate the performance of this pitch control strategy by using the computational fluid dynamics (CFD) method based on an in-house Navier–Stokes (N–S) equations solver. The turbulence model is the k−ω shear stress transport (SST) model. The inviscid spatial discretization scheme is the fifth-order modified weighted essentially non-oscillatory (WENO-Z) scheme. The effect of pitch control factor κ and amplitude angle A of this novel pitch control strategy on the power coefficient Cp, instantaneous torque coefficient CT of single blade and flow fields has been investigated from a low tip speed ratio (TSR) of 1.44 to high TSR of 3.3. The extensive studies show that this novel pitch control strategy can effectively improve the aerodynamic performance of VAWTs, especially at relatively low TSRs, and the optimal values of κ and A are 3° and 14°, respectively. The maximum absolute increase in power coefficient Cp can reach 0.2444 at TSR of 1.68, and the average absolute increase for all TSRs is 0.1346.

Analytical forming forces in two roller flow forming

Analytical forming forces in two roller flow forming

Assessment of Model Predictive Control for Mars Entry Vehicles with Flaps

Flap-based steering systems on blunt-body Mars entry vehicles may improve flight performance relative to existing bank-angle steering systems. Successful implementation of aerodynamic flaps on a hypersonic entry vehicle requires an active control system to map angle of attack and sideslip angle commands to flap deflection commands. Here, a successive-linearization model predictive control algorithm and a linear-quadratic regulator are designed and assessed to address this multiple-input, multiple-output control problem. These two control algorithms are assessed in the presence of uncertainty in Monte Carlo simulations for various flap configurations and command profiles. While both control algorithms provide successful command tracking in the presence of uncertainty, the model predictive controller tracking errors are about half the value of those corresponding to the linear-quadratic regulator, indicating improved performance. Large uncertainties sometimes result in the linear-quadratic regulator failing to maintain control of the vehicle, while the model predictive controller remains successful. A comparison of several flap configurations shows the model predictive controller can be applied to various flap configurations successfully with only marginal performance differences between configurations, while the linear-quadratic regulator has a larger performance disparity between configurations and may require additional tuning to avoid controller failures when changing configurations.

Mach, Reynolds, and Strouhal Number Effects on Deployable Aeroshell Pitch Dynamics

This paper presents a computational study exploring the dependence of oscillation rates and Mach, Reynolds, and Strouhal numbers on the dynamic stability of a mechanically deployable aeroshell. Computational fluid dynamics free-oscillation simulations are performed to compute the pitch damping coefficient with dependence on pitch rate. The pitch damping coefficient is split in its fore- and aftbody components. The aftbody loads are shown to excite the oscillations at low angles of attack. High values of Mach number tend to decrease the aftbody damping coefficient, supporting the theory that the instability stems from a delayed adjustment of the recompression shocks with motion. The wake flow structure changes considerably at low Reynolds numbers, leading to significant and unpredictable changes in the aftbody damping coefficient, with relevance for Mars entry and ground testing. Conversely, the forebody loads always damp the oscillations, with a forebody damping coefficient that results broadly independent of Mach and Reynolds numbers. It is further shown how the forebody damping coefficient increases considerably with Strouhal number. Previous studies rarely considered this influence and assumed its effects to be caused by changes in Mach number, potentially leading to inaccuracies when flying through different atmospheres or along different trajectories.

Flow Control over a Two-Element Airfoil Using a Dielectric-Barrier-Discharge Plasma Actuator

Flow control over a two-element airfoil using a symmetrical dielectric-barrier-discharge plasma actuator is studied at the Reynolds number of 1.1×105. The results demonstrated that the lift–drag ratio can be increased by about 21.8% without drag penalty after plasma actuation. Meanwhile, the time-averaged flowfield indicated that the separation region area around the flap is reduced by the plasma actuator. Moreover, the leading-edge stagnation point deflects toward the lower surface of the airfoil, which is similar to the effect of increasing the angle of attack and leads to the increment of the lift. In addition, the controlling mechanisms of the plasma actuator are uncovered based on the instantaneous flowfield results. It is of great importance that two flow structures produced by the interaction between the plasma actuator and the separated shear layer at different times play an important role in suppressing the separation flow by promoting the mixing between the main flow and the flow near the wall surface, and transferring the momentum from the leading edge of the flap to the trailing edge of the flap. The different characteristics of the separated shear layer at different times is the main reason for the generation of different flow structures of the plasma actuator.

Active Hinged Wingtip Control for Reducing Wing Root Bending Moment

The development of lighter and more efficient transport aircraft has increased the focus on reducing gust loads. One recent design innovation is the use of hinged wingtip devices to increase the aspect ratio, thereby enhancing aircraft performance. Experimental tests have demonstrated that passive hinged wingtips can provide additional gust load alleviation. This study introduces a brushed DC motor in the hinge to control wingtip rotation, improving gust load reduction through a proportional-derivative control. A lightweight wingtip was designed to be either free-hinged or actively controlled by the motor, with the motor configuration also allowing for a fixed wingtip option. Wind tunnel experiments were conducted to test responses to 1-cosine and harmonic gusts for all wingtip configurations to measure the root bending moment caused by gusts. Additionally, the effects of nonzero angles of attack at the root, simulating takeoff conditions, and varying starting fold angles of the wingtip were examined to determine their impact on root loads under gust conditions. The results showed that an active wingtip significantly reduces both positive and negative peaks in the root bending moment and identified some limitations of passive wingtips, such as flapping at higher gust frequencies.

On the Wake/Tailplane Interaction for Established Transonic Airfoil Buffet

Specific upstream flow conditions in transonic flight may incite a highly unsteady flow mode called transonic buffet. The associated periodic shock motion and intermittent separation are transported via the turbulent wake, eventually impinging on aerodynamic components downstream. A generic tandem configuration is investigated in the Trisonic Wind Tunnel of Institute of Aerodynamics (AIA) at M∞ of 0.72, consisting of a main wing (OAT15A) at an angle of attack of 5° and a tailplane (NACA 64A-110) at 0°; chord Reynolds numbers are 2.0×106 and 1.0×106, respectively. Focusing schlieren, particle image velocimetry, and unsteady pressure measurements are conducted to capture the buffet phenomenon, the evolving wake, and its interaction with the tailplane. Temporal and spectral properties of the buffet mode are shown to replicate those of an isolated airfoil but are slightly modified due to a mutual interaction. Periodic shock oscillations at Stc of 0.066 are coupled with intermittent flapping of the wake, which conveys the varying momentum deficit downstream and links both airfoil flow domains. The buffet phase effectively modulates the intensity of emitted vortical structures, imprinting the periodic buffet mode onto the tailplane. Resulting load fluctuations reveal the superposition of a high-frequency unsteadiness attributed to vortex shedding, indicating the greatest receptivity to disturbances around the airfoil suction peak.

Numerical Simulation of Self-Sustained Roll Oscillations of an 80-Degree Delta Wing Caused by Leading-Edge Vortices

Numerical simulations of an 80-degree delta wing in free-to-roll motion are performed by applying the dynamic fluid–body interaction (DFBI) model and the overlap/chimera method using the URANS equations. The capabilities of modern computational fluid dynamics methods for predicting wing-rock phenomena over a wide range of angles of attack at low Mach numbers and strong wing–vortex interaction, including the vortex breakdown phenomenon, were investigated by comparing simulation results with wind tunnel test data. At low angles of attack, delays in the strength and position of the leading-edge vortices above the wing have a destabilizing effect on it, leading to the emergence of self-sustained limit-cycle oscillations. At high angles of attack, where vortex breakdown occurs, the available wind tunnel data show that there are two modes of wing self-oscillations in free-to-roll motion, namely, regular large-amplitude oscillations and irregular small-amplitude oscillations, where the excitation of the latter mode depends on the angle of attack and the initial roll angle of the wing motion. The performed numerical simulation also shows the existence of these two self-oscillatory modes in roll, qualitatively and quantitatively matching the experimental data.

Aerodynamic performance analysis of NACA 0015 airfoil at low Reynolds numbers

This study aims to enhance the aerodynamic performance of a NACA 0015 series symmetric airfoil. The research was conducted using the Ansys Fluid Flow (CFD) module. The analysis area comprised 300,000 mesh elements. Several comparative analyses were conducted at low Reynold number (Re) and angles of attack ranging from α=-100 to 100. An increase in the angle of attack typically led to an elevation in the aerodynamic force coefficients (Cl, Cd, and Cl/Cd). In our study, the optimal values were attained at α=80, utilizing the Spalart-Allmaras turbulence model and Re=1×106, in comparison with analogous studies in literature. A 30% increase in lift coefficient (Cl) was attained relative to the initial condition. Furthermore, owing to the pressure differential between the lower and upper surfaces of the wing profile, the average velocity values recorded were 29.6 m/s and 18.1 m/s, respectively. Consistent with these findings, it is believed that this series, particularly favored in wind turbines, may operate more efficiently and effectively in the future with the test data acquired from experimental settings.

Lateral-directional wind tunnel tests of the PROSIB 19-pax aircraft model

This paper presents the power-off, lateral-directional wind tunnel tests on the fixed-wing, 19-passenger aircraft model developed within the Italian PROSIB project. The concept is an innovative small air transport airplane with distributed propellers and hybrid-electric powerplant. By measuring the aerodynamic forces and moments, the experimental investigation focused on the estimation of the power-off stability and control derivatives, highlighting the effects of the aerodynamic interference. Tests included a belly-mounted pod, simulating a battery storage unit, and two distinct empennage configurations: a body-mounted (low) horizontal tail and a T-tail (high). Numerical analyses were also used to further highlight the role of aerodynamic interference in the generation of forces and moments. For instance, wind tunnel data have shown a beneficial effect of the belly pod on the aircraft directional stability (+13%), but were in contrast with the results of numerical analyses (−30%). The measured sidewash depends also from the empennage layout, not only from the vertical tail planform area. Simulations confirmed an excessive directional stability with respect to the directional control in the ratio of 1.65, suggesting that such class of airplane should have a larger rudder chord ratio or a horn balance. Combined tests at different angles of attack and flap deflections revealed some issues on the lateral stability of the model, which are related to the velocity circulation on the wing in high-lift conditions counteracting the effective dihedral of the model’s layout. The collected dataset of aerodynamic derivatives will serve as reference for a next experimental investigation on the aero-propulsive effects and provide useful information to researchers and professionals involved in similar design studies.