Showing papers on "Pitching moment published in 2023"

Effect of Airfoil Design Parameters on Deep Dynamic Stall under Pitching Motion

Abstract: This paper presents an investigation of dynamic stall under a sinusoidal pitching motion using a parametric airfoil design. The parametric airfoil design method performs a parameterization starting from a baseline airfoil and then morphs it with different design parameters. These parameters include the camber, thickness, thickness crest position, leading-edge radius, trailing-edge camber, and boat-tail angle. OVERFLOW CFD is used to simulate the deep dynamic stall of a NACA 0012 airfoil. The airfoil is exposed to a freestream flow of Mach = 0.3 and Re = 3.76×10^6 and under a sinusoidal 15◦ ± 10 ◦ pitch oscillation with a reduced frequency of k=0.101. First, the numerical simulations are validated against experimental data for aerodynamic loads. Then, the peaks of the coefficients of lift, drag, and moment are compared to identify the trends and to analyze the significance of the effect of the changes in each design parameter. Furthermore, the effects of the different design parameters are analyzed with Morris’ sensitivity analysis in order to further assess their relative influences. The objective is to analyze how each airfoil geometry parameter influences the dynamic stall characteristics and to rank and assess the quantitative effect of these parameters on the dynamic stall characteristics. Overall, it has been found that the thickness crest position has a sizable influence on all the dynamic stall characteristics.

Aero-Propulsive Interactions between UAV Wing and Distributed Propellers Due to Their Relative Position

Abstract: The purpose of this paper is the evaluation of the aero-propulsive effects on a UAV wing model with distributed propulsion. An array of three propellers is placed ahead of the leading edge of a rectangular wing with flap. The investigation was performed with high-fidelity numerical analyses to provide insights into the phenomenology and to screen the interesting positions to be validated in the wind tunnel. The propellers’ array is moved into twelve different positions, allowing longitudinal and vertical translations. The wing has an untwisted and constant section profile, with a single slot trailing-edge flap that is deflected into three positions. The flap span is entirely covered by the propellers’ blowing. Results show an increment of lift, drag, and pitching moment coefficients with distributed propellers enabled. For a given thrust level, the magnitude of such increments depends on the propellers’ positions, the flap configuration, and the angle of attack. The lift enhancement sought in distributed propulsion applications comes at the expense of a significant increase in drag and pitching moment magnitude. In some combinations, the wing’s contribution to the aircraft longitudinal stability is severely affected. Conversely, the propellers’ inflow is altered such that thrust is increased in all the investigated configurations, with a small reduction of propulsive efficiency.

Force and torque reactions on a pitching flexible aerofoil

Abstract: Abstract Experimental measurements in a wind tunnel of the unsteady force and moment that a fluid exerts on flexible flapping aerofoils are not trivial because the forces and moments caused by the aerofoil's inertia and others structural tensions at the pivot axis have to be obtained separately and subtracted from the direct measurements with a force/torque sensor. Here we derive from the nonlinear beam equation general relations for the force and torque reactions at the leading edge of a pitching aerofoil in terms of the fluid force and moment on the aerofoil and its kinematics, involving geometric and structural parameters of the flexible aerofoil. These relations are validated by comparing high-resolution numerical simulations of the flow–structure interaction of a two-dimensional flexible aerofoil pitching about its leading edge with direct force and torque measurements in a wind tunnel.

HLPW-4: Wall-Modeled Large-Eddy Simulation and Lattice–Boltzmann Technology Focus Group Workshop Summary

Abstract: A summary of the nine submissions to the Wall-Modeled Large-Eddy Simulation and Lattice–Boltzmann (WMLESLB) Technical Focus Group (TFG) at the 4th High lift Prediction Workshop is provided. The focus of this TFG was to assess the current capabilities of WMLES and LB methods on a complex high-lift configuration across a wide range of angles of attack. Analysis of the submitted data suggests that [Formula: see text] spatial degrees of freedom are needed to accurately predict pitching moments at high angles of attack due to large pressure gradients present on the outboard slat and main element for [Formula: see text] (corrected for free-air). While some scatter is reported in pitching moment coefficient at the low-angles of attack ([Formula: see text]), excellent agreement is observed between submissions near the [Formula: see text] state. Objective superiority of WMLES methods over Reynolds-averaged Navier–Stokes (RANS) can be seen in terms of lack of excess outboard separation; a majority of the WMLES and LB submissions predict wedge-shaped separation patterns consistent with the experimental oil flow. The in-tunnel simulations show excellent agreement with the experiment in terms of a) integrated loads, b) surface flow-topology, and c) mechanism for the onset of inboard stall. Further evidence is provided to demonstrate both qualitative and quantitative superiority of the WMLES submissions over RANS.

Scaling and lateral maneuverability of pitching foil in periodic freestream

Abstract: We formulate the thrust and lift coefficients using scaling laws to develop a guideline for the lateral maneuverability of a pitching foil in a periodic freestream. The scaling laws for thrust and lift coefficients of two-dimensional pitching foil in a periodic freestream are derived by considering added mass and circulatory forces. We examined the validity of scaling laws by conducting water tunnel experiments at a Reynolds number of 4.2 × 103. The key parameters are the pitch amplitude and phase difference between the periodic freestream and pitching foil. The pitch amplitude was changed from 4° to 24° with 4° increments, and the phase difference was changed from 0 to 2 π with 0.25 π increments. It was discovered that our scaling laws were consistent with experimental data for small pitch amplitude. By using scaling laws, we proposed guidelines to control the thrust and lift coefficients for lateral maneuver. Our guideline demonstrates that pitch amplitude can be employed to control the thrust coefficient to cancel out drag, and the phase difference is useful to control the lift coefficient without changing the adjusted thrust coefficient.

Assessment of Turbulence Models for Unsteady Separated Flows Past an Oscillating NACA 0015 Airfoil in Deep Stall

Abstract: This paper provides 2D Computational Fluid Dynamics (CFD) investigations, using OpenFOAM package, of the unsteady separated fully turbulent flows past a NACA 0015 airfoil undergoing sinusoidal pitching motion about its quarter-chord axis in deep stall regime at a reduced frequency of 0.1, a free stream Mach number of 0.278, and at a Reynolds number, based on the airfoil chord length, , of . First, eighteen 2D steady-state computations coupled with the SST model were carried out at various angles of attack to investigate the static stall. Then, the 2D Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations of the flow around the oscillating airfoil about its quarter-chord axis were carried out. Three eddy viscosity turbulence models, namely the Spalart-Allmaras, Launder-Sharma , and SST were considered for turbulence closure. The results are compared with the experimental data where the boundary layer has been tripped at the airfoil’s leading-edge. The findings suggest that the SST performs best among the other two models to predict the unsteady aerodynamic forces and the main flow features characteristic of the deep stall regime. The influence of moving the pitching axis downstream at mid chord was also investigated using URANS simulations coupled with the SST model. It was found that this induces higher peaks in the nose-down pitching moment and delays the stall onset. However, the qualitative behavior of the unsteady flow in post-stall remains unchanged. The details of the flow development associated with dynamic stall were discussed

Aerodynamic Interaction and Analysis of Nose-Mounted Propeller Aircraft

Abstract: The paper deals with the aerodynamic analysis of a nose mounted propeller aircraft using the flow solver HiFUN. Unsteady RANS simulations using sliding mesh technology is performed on aircraft with propeller. The study on the aerodynamics of a propeller-driven aircraft is challenging because of the interaction of propeller slipstream with wing and other components, leading to the modification of force and moment coefficients of the aircraft, and performance parameters of the propeller as well. The effect of propeller slipstream on aircraft aerodynamics and the installation effects on propeller aerodynamics are studied using CFD. The regions on the aircraft influenced by the propeller slipstream is also identified by the means of pressure plots. The comparison of force and moment coefficients obtained from powered and unpowered simulations are also discussed and this includes a comment on the pitch stability of the aircraft. The results obtained from powered simulations are also compared with the flight stall tests. The work establishes the suitability of the present day CFD tools for the aerodynamic analysis of propeller driven aircraft, and the need for super-computing platform to accomplish the unsteady powered simulations.

Numerical Analysis of Dynamic Stall of a Tubercled Airfoil

Abstract: The intention of the present work is to analyse numerically the effect of tubercles on the aerodynamic performance of an airfoil section in dynamic conditions at a low Reynolds number. The performance analysis is done for the airfoil section, E216 and the lift trends for its pitching motion are studied. Numerical simulation is carried in ANSYS FLUENT. The transition SST (4 equation) viscous model is considered for the study. The results show that the lift coefficient increases while pitching up motion of the airfoil up to an angle of attack of 15°. A hysteresis loop is formed while plotting the lift coefficient against the angle of attack, indicating that the lift coefficient during pitching up is higher than that during pitching back for the same angle of attack. The tubercles reduce the lift coefficient but considerably reduce the hysteresis loop in the lift.

Multi Domain-Decomposed Reduced-Order Modelling of Steady Aerodynamics for 2D Store Separation Analysis

Abstract: Multi-body aerodynamic analysis is crucial whenever there is a store that separates from its parent aircraft. Certification of a store for use with an aircraft demands a meticulous analysis of the separation trajectory across a range of operating parameters (freestream conditions). The present work demonstrates an efficient albeit approximate technique that employs a reduced-order model (ROM) based on proper orthogonal decomposition (POD) for predicting the flow field around a store-aircraft dyad. The main innovation is a domain-decomposition approach which allows POD-based ROM to be used for the majority of the flow domain, keeping small regions that must be addressed by full-order simulations. Steady Reynolds-Averaged Navier Stokes (RANS) is used to generate the learning database for a particular set of operating conditions. The prediction of the lift and drag forces and pitching moment coefficients for a new set of operating conditions is performed using the proposed approach. Encouraging results are obtained in the validation that is pursued for simplicity on a two-dimensional problem; the approach applies to three-dimensional problems too.

Analysis of Aircraft Parking Stability Based on Atmosphere Boundary Theory

Abstract: Based on numerical simulation technology, the aerodynamic load research of civil aircraft parked on the ground is conducted. The CRM model parked on the ground is established by CFD software. Based on the atmospheric boundary layer theory, the seven incoming flow conditions for numerical calculation are designed. And the aerodynamic loads’ change of the aircraft model is calculated when the -90° sideslip angle. The result shows that the mooring load on the nose landing gear mainly comes from the longitudinal load caused by the upwards pitching moment on the flat tail and the lateral load caused by the yaw moment; since the rolling moment coefficient is less than the pitching moment coefficient by two orders of magnitude, which hardly affects the mooring load. The study provides a reference for reducing the mooring load of civil aircraft under heavy wind conditions.

Effect of Turbulence Intensity on Time-Averaged Aerodynamics of NACA0012 Wing at Low Reynolds Numbers

Abstract: In this study, we investigated the effect of the turbulence intensity and the aspect ratio of the NACA0012 airfoil at low Reynolds numbers. Moreover, we compared the effect of the turbulence intensity on nonlinearity between the 2D and 3D models. The angles of attack of the extrema of pitching moment coincide with the angle of attack of the changing lift slope. And the aerodynamic characteristics of the 3D models are similar to those of the 2D model. Aerodynamic testing results indicate that the nonlinearity of the aerodynamic characteristics decreases with increasing turbulence intensity for both the 2D and 3D models.

Modification on Static Response Under Wind Load: Effects of Rectangular Tall Building Vertical Chamfered Edge

Abstract: Now adays, due to architectural and structural requirements, complicated tall and slender buildings with various corner configurations and cross-sectional shapes are emerged, which are difficult to design using the existing wind load standards as well as using available software packages. For such conditions, an experimental study is the best solution to develop new standards and solve such design limitations. In this study a total of five rigid plywood models of equal height are prepared at a scale of 1:100, the principal model is a rectangular building with the geometry of B*D*H, 200mm*300mm*500mm and other models are vertically chamfered edges as B/8, B/4, 3B/8, and B/2. In properly designed open rectangular boundary layer wind tunnel with 2m*2m*15m simulation section at IIT Roorkee, India. The model is placed on the top floor and the mean wind velocity profile of approaching flow 9.61m/sec corresponding to terrain Category-II is allowed to pass through the circuit and various digital signal readings are taken at various wind incidences then converted to forces, moment, coefficients and results are compared with existing codes. As vertical chamfering size increases, twisting and torsional moment increases, drag force coefficient and lift-force coefficient increase due to the slenderness of the chamfered building compared with the principal building.

DLR Results for the 1.5 AIAA Stability and Control Prediction Workshop Investigating a Wing and Wing-Tail Section of the Common Research Model

Abstract: A summary about the DLR results for the Special Session of the AIAA Stability and Control Prediction Workshop regarding the wing section only and wing/tail section of the Common Research model (CRM) is presented. The first prediction workshop revealed a deficit in the accurate determination of the pitching moment coefficient of the Common Research wind tunnel model. Thus, the idea is to perform investigations on a wing only and wing/tail section to improve the prediction accuracy for the pitching moment, and in consequence pitching moment derivatives, to increase the prediction reliability for future workshops. The two-dimensional sections of the CRM wind tunnel model are used to calculate a transonic Mach number sweep for a given lift coefficient to explore mesh-independent solutions. Using aerodynamic coefficients and their partial and total derivatives, and determining the velocity vectors at a defined location provides insight into the different meshing strategies for both airfoils and the wing wake. In addition, DLR also computed the optional test cases by evaluating the lift coefficient range from zero to the maximum for the wing only and the wing/tail case, and evaluating the derivative of the pitching moment coefficient with respect to angle of attack and tail incidence angle for the wing/tail case. The analysis shows that the derivative prediction on the two-dimensional CRM case proves to be very sensitive regarding the grid quality, wing and tail incidence angle as well as the shape of the tail geometry.

Experimental Study on Dynamic Stall of Airfoil in Rotor Reverse Flow Region

Abstract: The large reverse flow region of the rotor with a high advance ratio is an important factor that affects the performance improvement of helicopters. This paper examines the dynamic stall of the airfoil in the reverse flow region of the rotor to develop a set of dynamic pressure measurement systems for the airfoil in the reverse low region. The pitch oscillation experiment of the NACA0018 airfoil in and out of the rotor reverse flow region has been carried out, and the influence of the airfoil motion parameters on dynamic stalls has been studied. The results show that the airfoil is more likely to stall in the reverse flow region under static conditions and that stall is invariant to the Reynolds number. After a stall occurs, the lift coefficient decreases more slowly with the increase of the angle of attack (about 10% of that in the forward flow state). Under the dynamic environment, in a pitching cycle, the quarter chord moment coefficient of the airfoil alternates between positive and negative frequently during reverse-blowing. The pitching oscillation in the reverse flow region is more sensitive to the changes in airfoil parameters than that under normal flow, and there is a marked difference. The alternating moment of the airfoil in the reverse flow region is significant: the greater the pitching amplitude, the greater the alternating moment. In the reverse-blowing state, with the increase in reduced frequency, the dynamic stall angle of attack increases more significantly.

Sinusoidal Gust Response of RC Propellers in Tandem Configuration

Abstract: The study of the fixed-pitch small-scale propeller under sinusoidally time-varying freestream is extended to a tandem propeller configuration. The changes in thrust and pitching moment of both the front and back propeller were characterized when encountering the sinusoidal gust in edgewise flight conditions. The propeller's steady freestream performance obtained in the previous study was used to predict response under sinusoidal time-varying freestream in edgewise flight. Below a reduced frequency of 0.2, the propeller response agrees with the prediction model, suggesting a linear superposition and quasi-steady dynamics for the propellers. At a higher reduced frequency, a reduction in mean thrust and pitching moment was measured. A phase lag in the propeller response was also observed indicating an unsteady response of the propeller. When placing the propeller in close proximity to each other, additional variations in the back propeller's performance were also observed at higher reduced frequencies, creating additional instability in the system.

Aerodynamic Performance of Swept Wings in Unsteady Streamwise Flow

Abstract: The aerodynamic response of two finite-span wings with sweep angles of 0° and 30° was studied under the impact of a convectively unsteady freestream. To assess the aerodynamic response, the unsteady total lift and pitching moment measurements were collected and analyzed, along with time-resolved pressure distributions at select locations across the wingspan. The convective nature of the unsteady freestream generates a streamwise velocity that varies both temporally and spatially over the wing surface, generating spatial velocity gradients that are acceleration dependent. The total lift coefficient response was found to be similar for the unswept and swept wings, while the hysteresis in the total pitching moment coefficient is magnified with increased sweep angle.

Numerical Investigation of a Dynamically Morphing UAS-S45 Wing Airfoil at moderate Reynolds number

Abstract: The unsteady flow characteristics and responses of the UAS-S45 airfoil with a morphing trailing edge shape at high angles of attack undergoing deflections are investigated at a Reynolds number of 2.4 × 106. The flexible trailing edge was simulated using a computational fluid dynamics approach using a dynamic mesh and user-defined functions. The goal was to achieve a dynamically deflected trailing edge in an unsymmetrical airfoil and assess the influence of unsteady morphing trailing edge deflection on transient forces and flow field unsteadiness. The steady aerodynamic characteristics of the morphing deflection and the conventional deflection was initially studied. Then, the unsteady aerodynamic characteristics of the morphing wing was investigated as the trailing edge deflects at different rates. The dynamic flow responses to downward deflections are studied using the turbulence model. The time histories of the lift and drag coefficient responses exhibit a proportional relationship between the morphing frequency and the slope of response at which these parameters evolve. Coefficients of lift, drag, and moment of the deflected trailing edge airfoils were compared to those of the reference airfoils for various angles of attack. The numerical results show that the transient lift coefficient in the deflection process was higher than that of the static case at different angles of attack. The transient lift coefficient were higher as the deflection frequency increased. It was also revealed that the trailing edge deflection did not favor the flow reattachment. In addition, the dynamic mesh strategy, cell quality, and the proposed method of deforming the morphing trailing-edge was presented. increased. It was also revealed that the trailing edge deflection did not favor the flow reattachment. In addition, the dynamic mesh strategy, cell quality, and the proposed method of deforming the morphing trailing-edge was presented.

Off-Board Aerodynamic Measurements of Small-UAVs in Glide and Powered Flight Using Motion Tracking

Abstract: Aerodynamic estimation of small UAVs operating at Reynolds numbers less than 30, 000 can be cumbersome and expensive due to the size of the vehicles and the magnitude of the resulting forces and moments. The current paper explores an off-board aerodynamic measurement method using motion tracking technology. The UMX-Vapor and F4U-Corsair aircraft in un-powered glide flight are used as the baseline aircraft configurations. The trajectory tracking system was validated through a set of static and dynamic tests to account for uncertainties and errors. Multiple flight trajectory data was processed to obtain the aircraft’s force and moment behavior as a function of angle-of-attack in quasi-steady conditions. The lift, drag, and moment data is compared with existing literature and theory to further validate the system

Flowfield Analysis of a Quadrotor in Forward and Maneuvering Flight Modes

Abstract: The paper presents a flow field characterization study of a small quadrotor via static and dynamic Particle Image Velocimetry tests that were performed at ODU low-speed wind tunnel. Differential rotor RPM levels were tested with 6 m/s and 12 m/s wind speeds at a 1 Hz pitching motion rate. Flow topology of the quadrotor at 0° and +10° (nose-up) mean pitch angles are the main interest of the paper, since nonlinear pitching moment behavior is observed at these conditions. It was shown that the highest inflow disturbance occurs at +10° mean pitch oscillation for 12 m/s which causes unsteady transient effects on the pitching moment of the quadrotor.

Multi-Objective Airfoil Optimization Under Unsteady-Freestream Dynamic Stall Conditions

Abstract: Aimed at alleviating dynamic stall, an optimization method for rotor airfoils is proposed considering the unsteady-freestream circumstance and pitching motion. The method is based on the unsteady Reynolds-averaged Navier-Stokes equations, kriging model, and non-dominated sorting genetic algorithm II (NSGA-II). Three objective functions are built for minimizing the area of lift hysteresis loop, value of peak drag, and peak pitching moment. An optimized airfoil with larger maximum thickness, maximum camber, and upper leading-edge radius is obtained based on the baseline SC1095 airfoil. Besides, the optimized airfoil shows smaller local thickness and camber near the trailing edge. The results show that the flow separation and dynamic stall are suppressed or alleviated under both design and off-design conditions, attributed to a significant reduction of negative pressure peak and adverse pressure gradient. The dynamic stall is also alleviated for the rotor configured with the optimized airfoil in forward flight. This indicates that the optimized airfoil performs well in a rotor environment.

The cubic pitching moment coefficient of spin-stabilized projectiles

Abstract: This technical note presents a feasible method to effectively predict the cubic pitching moment coefficient for spin-stabilized projectiles. First, a surrogate model for predicting the cubic moment coefficient is constructed by using the Kriging method to relevant published data of several typical spin-stabilized projectiles. The result of a wind tunnel test validates the accuracy of the Kriging prediction, implying that this prediction model complements the current research literature. Second, the global sensitivity analysis combined with this prediction model is used to assess the effect of the shape parameters of spin-stabilized projectiles on the cubic pitching moment coefficient. As a result, the relationship between the shape parameters and the nonlinear pitching moment coefficient is preliminarily explored. The results of an example show that the cylindrical part length, the head shape parameter and the nose length have greater influence, whereas the boat-tail length has the weakest influence.

Numerical Investigation of the Effect of Trailing-Edge Morphing on Dynamic Stall using Delayed Detached Eddy Simulations

Abstract: This paper presents a study on the effect of trailing-edge morphing on dynamic stall using delayed detached eddy simulations (DDES). The dynamic stall of a NACA 0018 airfoil is simulated using OVERFLOW CFD, with a freestream Mach number of 0.1 and Reynolds number of 200,000, undergoing a ramp-up pitching motion. First, DDES numerical simulations are used to predict and analyze the aerodynamic loads for the baseline NACA 0018 airfoil and two trailing-edge morphing geometries. The peaks of the coefficients of lift, drag, and moment for the baseline case and the morphed cases are compared to identify trends and percent differences, and to analyze the significance and effect of the trailing-edge morphing design parameter. It is found that modifying the trailing-edge angle has global effects on dynamic stall. For example, the morphed trailing-edge airfoil yields a sizable reduction in the pitching moment without compromising the loss of lift by too much. The dynamic stall development stages, as well as the detailed flow physics and flow features, are analyzed. It is found that the morphed airfoils exhibit stronger secondary shear layer separation in the middle and aft airfoil sections at higher angles of attack (AoAs), compared to the baseline airfoil. It is also found that the morphed trailing-edge with the largest selected design parameter causes the laminar separation bubble (LSB) to burst at an earlier stage, resulting in the dynamic stall vortex (DSV) occurring at an earlier stage compared to the baseline case.

Analysis of the unsteady surface pressure distribution of a pitching airfoil using modal decomposition

Abstract: This work presents an exploratory attempt to understand how modal decomposition can be utilized for characterizing the behavior of the unsteady surface pressure distribution on a pitching airfoil. The unsteady aerodynamics of a thick airfoil geometry across a wide range of conditions were studied. Analyzing the pressure distributions across cases with different levels of flow separation yielded results that exhibited transitional behavior that encouraged modal analysis. The utility of the Proper Orthogonal Decomposition in capturing the distinct physical features of the unsteady pressure distribution was then evaluated. The first four global spatial modes extracted from surface pressure data resemble important and understandable attributes of the pressure distribution for an oscillating airfoil. The four-mode description sufficiently reconstructs the surface pressure data even for conditions with complex unsteady flow interactions. The resulting reconstructed pressure distributions can be used to approximate lift and moment coefficients with good accuracy.

Identification and Modeling Method of Longitudinal Stall Aerodynamic Parameters of Civil Aircraft Based on Improved Kirchhoff Stall Aerodynamic Model

Abstract: The stall aerodynamic model based on Kirchhoff’s theory of flow separation is widely used in the identification and modeling of stall aerodynamic parameters. However, it has two defects. First, its model structure is significantly different from the pre-stall model used for a small attack angle, meaning the identification results cannot be combined with the pre-stall model to form the full flight envelope model. Second, the pitching moment model, which is used in conjunction with the Kirchhoff lift model, cannot accurately describe the aircraft stall pitching moment characteristics. To ensure the compatibility of the two models, this paper proposes a method to determine some unknown parameters in the stall model. The mechanism for the pitching moment generation of the aircraft stall is analyzed, and two high-order correction terms are added to the pitching moment model to better describe the longitudinal stall aerodynamic characteristics. Based on the identification of aerodynamic parameters, a longitudinal stall aerodynamic modeling method used for the aircraft stall process is developed. The identification and simulation validation results based on the quasi-steady stall flight data of a civil aircraft show that the improved stall model can accurately describe the quasi-steady stall pitching moment. The established stall aerodynamic model can accurately characterize the longitudinal quasi-steady stall aerodynamic characteristics of aircraft under different stall degrees.

Aerodynamic Coefficients of a Microspoiler for Spin-Stabilized Projectiles

Abstract: In this paper, the aerodynamic coefficients of a microspoiler for a spin-stabilized projectile are studied using a computational fluid dynamics (CFD) simulation. To guarantee an effective study, the CFD simulation methodology is validated by the current literature and a wind-tunnel test. As a result, the additional axial force coefficient, additional normal force coefficient, and normal moment coefficient are obtained and varied with a wide range of Mach numbers (from 0.6 to 2.0), angles of attack (from 0 to 30°), and aerodynamic roll angles (from 0 to 180°). The numerical simulation results show that, in addition to the freestream Mach number and the angle of attack, the effect of the aerodynamic roll angle on the additional axial force and normal force coefficients cannot be negligible. By observing and analyzing a series of pressure field plots around the uncontrolled and controlled projectiles, some important phenomena are reasonably discussed. It was found that the complicated variation in the aerodynamic coefficients of the microspoiler is induced by flow modifications, such as the pressure distribution around the projectile. The results of this research are expected to be supplementary to those concerning the aerodynamic characteristics of spin-stabilized projectiles with microspoilers, as concluded in the current literature.

Vortex Dynamics of a Separated Wing in a Time-Varying Freestream

Abstract: Abstract Unsteady flows threaten the performance and efficiency of systems operating in gusty environments. The impact of an unsteady freestream, generated in a closed test-section unsteady wind tunnel, on the flow separation and aerodynamic performance of a wing at a post-stall angle of attack is examined within the current study. Synchronized two-dimensional, high-speed particle image velocimetry and integrated surface pressure measurements were collected for a finite-span wing in a time-varying, spatially uniform freestream. Freestream accelerations impose additional unsteady pressure gradients within the wind tunnel that alter the behavior of shed vortical structures within the separated flow above the wing. Freestream acceleration and conservation of circulation determine the orientation and interaction of shed vortical structures, which alter the magnitude of the fluctuations in the lift force and pitching moment experienced by the wing. Specifically, fluctuations in the sectional lift and pitching moment coefficients are amplified during deceleration and attenuated during acceleration.