Showing papers on "Pitching moment published in 2022"

HLPW-4/GMGW-3: Wall-Modeled LES and Lattice-Boltzmann Technology Focus Group Workshop Summary

Abstract: A summary of the nine submissions to the Wall-Modeled LES 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 Lattice Boltzmann methods on a complex high-lift configuration across a wide range of angles of attack. Preliminary analysis of the submitted data suggests that > 250M 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 AoA > 17◦ (corrected for free-air). While some scatter is reported in pitching moment coefficient at the low-angles of attack < 11◦ - likely caused by differences in flap separation possibly due to low Reynolds number effects - excellent agreement is observed between the submissions near the CLmax state. Objective superiority of WMLES methods over steady state RANS can be seen in terms of lack of excess outboard separation; a majority of the good quality WMLES and LB submissions predict wedge-shaped separation patterns consistent with the experimental oil flow. Differences in the onset of stall mechanism in the free-air configuration for AoA > 20◦ is reported with two distinct topologies observed. Topology A is characterized by the onset of corner-flow separation which progressively grows to produce a pitch break in free-air with an angle of attack increase from AoA = 20.55◦ to AoA = 21.47◦ + eps where eps is a small perturbation (varying between submissions and likely to be within ±0.3◦). Topology B is characterized by boundary layer weakness emanating from the inboard side of the wing-pylon juncture substantially larger than any weakness in the wing-body juncture (due to corner-flow); submissions in this category do not show any tendency for occurrence of a pitch break for the free-air configuration within the vicinity of AoA = 21.47◦. The in-tunnel simulations submitted by 3 participants using different discretizations, grids and closure models 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 all 3 WMLES submissions over a representative steady state RANS submission to the workshop.

Unsteady aerodynamic prediction for iced airfoil based on Multi-Task Learning

Abstract: Ice accretion on wind turbine blades and wings changes the effective shape of the airfoil and considerably deteriorates the aerodynamic performance. However, the unsteady performance of iced airfoil is often difficult to predict. In this study the unsteady aerodynamic performance of iced airfoil is simulated under different pitching amplitude and reduced frequencies. In order to efficiently predict of aerodynamic performance under icing conditions, a multi-fidelity reduced-order model based on multi-task learning is proposed. The model is implemented using lift and moment coefficient of clean airfoil as low-fidelity data. Through using, the model can achieve aerodynamic prediction for different ice shapes and pitching motions. The results indicate that compared with single-fidelity and single-task modeling, the proposed model can achieve better accuracy and generalization capability. At the same time, the model can be generalized to different ice shapes, which can effectively improve the unsteady prediction efficiency.

Aerodynamic performance of traveling road vehicles on a single-level rail-cum-road bridge under crosswind and aerodynamic impact of traveling trains

Abstract: ABSTRACT Crosswind and train-induced wind are major factors influencing the aerodynamic performance of vehicles on single-level rail-cum-road bridges. Based on computational fluid dynamics (CFD) technology, this work developed a numerical model to discuss relevant issues. The flow features of the vehicle-bridge system, the influence of different lanes and vehicles are explored, and the superposition of crosswind and train-induced wind has been analyzed. The results indicate that the crosswind and train-induced wind superpose near the windward side of the concrete wall, producing two high-pressure and low-pressure zones, which are the primary cause of the aerodynamic variations on nearby vehicles. The crosswind decreases the variation amplitude of side force, rolling moment and yawing moment for 10% ∼ 20%, but the influence on the lift force and pitching moment is not significant. Therefore, the aerodynamic forces of the vehicle while meeting the train at different wind speeds can be obtained by superposing the aerodynamic variation caused by the moving train and the aerodynamic forces at its sole-traveling state, which are conservative and can provide references for actual engineering.

Propeller Position Effects over the Pressure and Friction Coefficients over the Wing of an UAV with Distributed Electric Propulsion: A Proper Orthogonal Decomposition Analysis

Abstract: New propulsive architectures, with high interactions with the aerodynamic performance of the platform, are an attractive option for reducing the power consumption, increasing the resilience, reducing the noise and improving the handling of fixed-wing unmanned air vehicles. Distributed electric propulsion with boundary layer ingestion over the wing introduces extra complexity to the design of these systems, and extensive simulation and experimental campaigns are needed to fully understand the flow behaviour around the aircraft. This work studies the effect of different combinations of propeller positions and angles of attack over the pressure coefficient and skin friction coefficient distributions over the wing of a 25 kg fixed-wing remotely piloted aircraft. To get more information about the main trends, a proper orthogonal decomposition of the coefficient distributions is performed, which may be even used to interpolate the results to non-simulated combinations, giving more information than an interpolation of the main aerodynamic coefficients such as the lift, drag or pitching moment coefficients.

Uncertainty quantification of wind turbine airfoil aerodynamics with geometric uncertainty

Abstract: An artificial neural network based reduced order model (ROM) is developed to predict the load coefficients and performance of wind turbine airfoils. The model is trained using a representative database of 972 wind turbine airfoil shapes generated by perturbing the design parameters in each of 12 baseline airfoils defining commercially relevant modern wind turbines. The predictions from our ROM show excellent agreement with the CFD data, with a 99th percentile maximum errors of 0.03 in lift-coefficient, 2 in lift-to-drag ratio and 0.002 in pitching moment coefficient. A Monte-Carlo based uncertainty quantification (UQ) and global sensitivity analysis (GSA) framework is developed using this computationally economical ROM. Using UQ, we observed the stall behavior to be very sensitive to geometric uncertainty, with more than 10% deviation in lift coefficient associated to 5% deviation in geometric features. Sobol’s analysis is used to identify the most influencing geometric feature for the stall behavior to be concentrated at the maximum thickness location on the airfoil suction surface.

Fixed Grid RANS Results and Turbulence Model Investigation using Simcenter STAR-CCM+ for 4thAIAA CFD High Lift Prediction Workshop

Abstract: This paper presents the results of fixed grid RANS turbulence model investigation performed with Simcenter STAR-CCM+ for the 4th AIAA High Lift Prediction Workshop. The analysis focuses on prediction of the maximum lift and understanding the different factors that have impact on near-stall simulation. The presented discussion includes validation of the SA model implementation available in Simcenter STAR-CCM+ executed on different grid families. The verification study demonstrates the impact of the chosen grid topology on the verification results and the changes in the simulation behavior depending on the choice of the turbulence model. The observations from the verification study are consistent with the nominal angle of attack results on the high lift Common Research Model, with Lag EB model predicting the highest lift. Obtained force coefficient polars show similar force values for different methods at low incidences and a large spread in the predicted forces close to the stall angle. The pitching moment coefficient predictions are most sensitive to the choice of the turbulence model even at the nominal angles of attack, with only the Lag EB model predicting values similar to the experimental data. The modified SST model predicts the lift behavior up to the wing stall. Lag EB results follow the experiment but separate prematurely due to wing-root junction separation. Runs using SA are dominated by outboard wing separation and fail to match the experiment. The presented work demonstrates that RANS can be used to successfully predict both integrated quantities and flow behaviors for high-lift configurations at low-to-moderate angles of attack, provided that adequate turbulence modelling is used. RANS can also predict the correct stall mechanisms but not the exact angle at which stall occurs.

Identification and Validation of the Cessna Citation X Longitudinal Aerodynamic Coefficients in Stall Conditions using Multi-Layer Perceptrons and Recurrent Neural Networks

Abstract: The increased number of accidents in general aviation due to loss of aircraft control has necessitated the development of accurate aerodynamic airplane models. These models should indicate the linear variations of aerodynamic coefficients in steady flight and the highly nonlinear variations of the aerodynamic coefficients due to stall and post-stall conditions. This paper presents a detailed methodology to model the lift, drag, and pitching moment aerodynamic coefficients in the stall regime, using Neural Networks (NN). A system identification technique was used to develop aerodynamic coefficients models from flight data. These data were gathered from a level-D Research Aircraft Flight Simulator (RAFS) that was used to execute the stall maneuvers. Multilayer Perceptrons and Recurrent Neural Networks were used to learn from flight data and find correlations between aerodynamic coefficients and flight parameters. This methodology is employed in here to optimize neural network structures and find ideal hyperparameters: training algorithms and activation functions used to learn the data. The developed stall aerodynamic models were successfully validated by comparing the lift, drag, and pitching moment aerodynamic coefficients predicted for given pilot inputs with experimental data obtained from the Cessna Citation X RAFS for the same pilot inputs.

Parameterizing Airfoil Shape Using Aerodynamic Performance Parameters

Abstract: A novel shape parameterization for airfoils (named as PAERO) is proposed to provide design variables related to the aerodynamic characteristics based on the linearized aerodynamic theory. The idea is inspired by the classical thin airfoil theory. Instead of describing the airfoil geometry explicitly, the mean camber line of an airfoil can be implicitly defined by the vortex distribution on the chord line that is expressed by a Fourier series in the thin airfoil theory. The Fourier series is parameterized by the Fourier coefficients specified by users. Within the frame of linearized aerodynamic theory, the first three Fourier coefficients are determined by the angle of attack, lift coefficient, and pitching moment coefficient, naturally providing three aerodynamic performance parameters. Then, the airfoil shape parameterization is completed by further parameterizing the thickness distribution by either the Class-Shape-Transformation method or the B-splines, depending on the specific applications. The test results show that the proposed shape parameterization has the same ability of fitting the existing airfoils as the traditional Class-Shape-Transformation method, but providing more aerodynamic performance parameters that are proved to be highly useful in applications.

Computational Validation That Whiffling-Inspired Gaps Require Less Work for Roll Control Than Conventional Ailerons at High Rolling Moment Coefficients

Abstract: Several species of birds have been known to invert in flight to lose altitude — a behavior known as whiffling. When the bird flies inverted, the flight feathers twist open to create gaps in the trailing edge of the wing, decreasing the lift produced by the wing. Gaps along the trailing edge of an aircraft wing were inspired by the feather rotation mechanism during whiffling, and asymmetrically applying these gaps on only one side of the wing produces a rolling moment due to the lift differential across the full wing. Previous experimental data and analytical estimates showed that whiffling-inspired gapped wings can produce a larger rolling moment coefficient than a conventional aileron, for a fraction of the actuation work. In the current work, we perform a computational study using Siemens STAR-CCM+ to estimate the work required to actuate nine gaps along the trailing edge of a whiffling-inspired wing and compare it to that of a representative aileron configuration. We show that the results of the simulation agree well with the prior experimental results. The results indicated that the work on the entire gap area may be higher than the work to deflect an aileron, however, the analytically estimated work on a smaller, more realistic, area corresponding to a gap cover was substantially lower than the work to deflect an aileron. These results provide evidence that sliding gaps that open in the plane of a wing require less work than deflecting an aileron into the flow for rolling moment coefficients above 0.0139. This computational validation is the first step in determining if smart materials can be used for this type of wing morphing. In all, the whiffling-inspired gapped wings could provide a far more energy-efficient method of roll control for energy-constrained fixed-wing uncrewed aerial vehicles than conventional ailerons, particularly at higher rolling moment coefficients.

Unsteady Aerodynamic Modeling and Analysis of Load Distribution for Helicopter Rotor Blades

Abstract: The complexity of the kinematics and aerodynamics of rotors is a challenging problem for achieving accurate modeling for prediction of rotor loads. The present paper describes an unsteady a...

Hypersonic Flow Control of Kinzhal Missile via Off-Axis, Pulsed Energy Deposition

Abstract: The interaction of an off-axis, spherical energy discharge with the Kh-47M2 Kinzhal missile at Mach 6 sea-level conditions was simulated. A parametric study of the energy discharge parameter (proportional to the ratio of the energy added to the internal energy within the energy deposition volume) was performed to examine the effect of energy added to the heated region in front of the missile and the changes it causes on the drag force, side (vertical) force, and pitching moment. The peak value for the pitching moment coefficient was shown to be 0.0045 for , which was shown to be 15.5% of the value due to a 10° front finset deflection. Both inviscid and Reynolds-averaged Navier–Stokes simulations were performed. The additional influence of the turbulent boundary layer on the peak value of the produced pitching moment was negligible. The time interval for the variation in the pitching moment coefficient due to energy deposition is 61 times faster than the standard actuation time (0.1 s) for conventional control surfaces, indicating the potential for multiple pulsed energy depositions as a means for hypersonic flight control.

Computational Investigation of Multirotor Interactional Aerodynamics with Hub Lateral and Longitudinal Canting

Abstract: This study investigates the interactional aerodynamics for laterally and longitudinally canted two-rotor systems with a front rotor and an aft rotor aligned with the flow. The -diameter, three-bladed fixed-pitched rotors are simulated using computational fluid dynamics at a targeted disk loading and 30 kt edgewise freestream. Simulations are performed using the commercial Navier—Stokes solver AcuSolve with a detached eddy simulation model. In addition to an uncanted case, two laterally canted cases (10° advancing sides up and 10° advancing sides down) as well as two longitudinally canted cases (10° inward and 10° outward) are simulated. Aft rotor performance is compared to isolated rotors operating at the same revolutions per minute, speed, and shaft tilt angle in order to quantify the effect of rotor–rotor aerodynamic interaction. For all configurations, the aft rotors experience a lift deficit at the front of the rotor disk, which also results in a nose-down pitching moment relative to an isolated rotor. The lift deficit for the uncanted rotor was around 15%. Lateral canting only slightly increases the lift deficit (to 16–18%) but also produces 28–38% change in roll moments. Change in aft rotor nose-up pitching moments for the uncanted and laterally canted rotors were in the 55–64% range. Longitudinal canting produces larger changes in the magnitude of the lift deficit and pitching moment, but has minimal effect on roll moments. In particular, canting inward results in a lift deficit as high as 21% and a 94% change in pitching moment. Canting outward, on the other hand, reduces the aft rotor lift deficit to 11% and the pitching moment change to 19%. The paper explains the changes in the flowfield and the underlying physics for the different cases in detail.

Unsteady Aerodynamic Modeling and Analysis of Load Distribution for Helicopter Rotor Blades

Abstract: The complexity of the kinematics and aerodynamics of rotors is a challenging problem for achieving accurate modeling for prediction of rotor loads. The present paper describes an unsteady aerodynamic model based on strip theory for the prediction of local aerodynamic loads on helicopter blades in translational flights. The proposed model accounts aerodynamically for unsteady behavior, poststall, leading-edge suction, and, structurally, local elastic torsion. Also, the local pitching moment coefficient is calculated according to the local parameters of both aerodynamic characteristics and unsteady angle of attack. A case study with published experimental data is selected to validate the model for the same operating conditions. The case is the 7A rotor high-speed test (point 312) performed in the French Space Lab’s (ONERA) S1MA wind tunnel in Modane-Avrieux, France. The proposed model is capable of predicting, qualitatively, the variation in both local normal force and pitching moment coefficients. Computational solver results are compared with experimental results to qualitatively clarify the physical differences between them. The main conclusion is that the proposed model calculations generally reflect the same trends as the test data, providing confidence in the ability to increase the model’s fidelity in calculating the aerodynamic behavior of rotors.

Two-Dimensional URANS Numerical Investigation of Critical Parameters on a Pitch Oscillating VAWT Airfoil under Dynamic Stall

Abstract: In this paper, a thorough 2D unsteady computational fluid dynamic analysis was performed on a pitching airfoil to properly comprehend the dynamic stall and aerodynamic forces. The computational software ANSYS Fluent was used to solve the unsteady Reynolds-averaged Navier–Stokes equations. Low Reynolds number flows were modeled using the k-ω shear stress transport turbulence model. Aerodynamic forces, fluid flow structures, and flow separation delay angles were explored as a function of the Reynolds number, reduced frequency, oscillation amplitude, and mean angle of attack. The maximum aerodynamic forces, including lift, drag, and the onset of the dynamic stall, were all influenced by these variables. The critical parameters that influenced the optimum aerodynamic forces and ended up causing dynamic stall delay were oscillation amplitude and mean angle of attack. The stall angle was raised by 9° and 6°, respectively, and a large increment in the lift coefficient was also noted in both cases. Additionally, for the highest Reynolds number, a considerable rise in the maximum lift coefficient of 20% and a 28% drop in drag coefficient were observed, with a 1.5° delay in the stall angle. Furthermore, a significant increase of 33% in the lift force was seen with a rise of 4.5° in the stall angle in the case of reduced frequency.

Pitch/Plunge Equivalence for Dynamic Stall of Unswept Finite Wings

Abstract: Pitch/plunge equivalence for deep dynamic stall of a straight finite wing is considered by employing large-eddy simulations. The flowfields are computed with a well-established time-implicit high-fidelity large-eddy simulation approach. The wing has a moderate aspect ratio of and a NACA 0012 section incorporating a rounded tip. The flow parameters are a freestream Mach number of and chord Reynolds numbers of . Pure pitching and equivalent plunging maneuvers are considered with a reduced frequency of and minimum and maximum effective angles of attack of 4 and 22 deg, respectively. The pitch and plunge dynamic stall cases are compared in detail in terms of the unsteady three-dimensional flow structure, surface pressure, and loading. Differences in the lift and moment coefficient are shown to be correctable, employing a steady thin-airfoil theory for a cambered airfoil that accounts for the rotation-induced apparent camber present in the pitching case. This pitch/plunge equivalence is extendable to the dynamic stall of a swept wing, as demonstrated in another paper by the authors [“Pitch–Plunge Equivalence for Dynamic Stall of Swept Finite Wings,” AIAA Journal (submitted for publication)].

Comparative study over double wedge and biconvex airfoils for laminar flow using CFD

Abstract: This paper is mainly focused on Supersonic Laminar Flow at Mach 3 for biconvex and double wedge airfoils. The coefficient of lift (Cl), coefficient of drag (Cd), and coefficient of moment along the respective airfoils are being analysed. The geometry of these is generated using the Designmodeler of ANSYS. Further, meshing is also achieved by ANSYS with around 50000 nodes which is satisfactory for the current flow analysis. The total number of iterations being set for the particular simulation is 1000. This article covers the approach of the Kutta-Joukowski theorem, from which we know that flow circulation impacts the lift of the airfoil and how it changes for biconvex and double wedge airfoils. Decisively, this paper delivers provides pressure, heat transfer, and velocity distribution for both the airfoils. This paper gives a comparative study of both the double wedge and the biconvex airfoils at MACH 3, zero angle of attack. The study will be analysing both the airfoils in 3D as well as in 2D.

High-Lift Computational Strategy for Slotted, Natural-Laminar-Flow Airfoils

Abstract: This work uses a computational fluid dynamics approach to evaluate the ability of the aft element of a slotted, natural-laminar-flow airfoil, designed for transonic applications, to function as a high-lift device. The analysis is based on the Reynolds-averaged Navier–Stokes equations with a laminar–turbulent transition model for subsonic flow at representative flight conditions and a fully turbulent model for the aft-element optimization. Results obtained at angles of attack near maximum lift contribute to the understanding of stall characteristics and show that maximum aerodynamic efficiency is obtained with a constant slot width between the flap and main element. Results indicate that the microflap can augment the effectiveness of the aft element. Drag calculations when compared with angle of attack and lift show insight on the aerodynamic efficiency of the microflap system in landing as a lift effector, as well as a drag device. Pitching-moment data are also presented for completeness. Results obtained with Fowler flaps are consistent with other studies of extended-flap configurations; more specifically, the aforementioned velocity ratio decreases toward the aft-element trailing edge, indicating that the multi-element high-lift system is operating as intended.

Improving Dynamic Stall Effects Using Leading Edge Tubercles

Abstract: This paper investigates the application of leading-edge tubercles, for reducing aerodynamic drag and nose-up pitching moments, as well as mitigating hysteresis during dynamic stall. The effect of different tubercle shapes are evaluated using transient computational fluid dynamics models at different flight conditions. Results suggest a reduction of drag, and moment hysteresis of 29.4% and 34.5%, respectively, averaged over all flight conditions, compared to the baseline straight leading-edge model. This improvement comes with a lift decrease penalty of 8.9%. Additionally, the maximum drag and nose-up pitching moments are reduced through the application of leading-edge tubercles, with minimal change in maximum lift.

Study on Nonlinear Aerodynamic Characteristics of a Semi-Closed Box Bridge Deck Based on Coupled Amplitude Variation

Abstract: This paper explores the nonlinear characteristics of the self-excited aerodynamic forces of a semi-closed box deck section to perfect the theory of aeroelastic response analysis. A numerical wind tunnel model was established based on the computational fluid dynamics (CFD) method. The heaving-pitching coupled motion is realized by loading user-defined function (UDF) and dynamic grid technology. The self-excited aerodynamic forces varying with amplitude are identified and analyzed, and the reliability of the aerodynamic results obtained by numerical simulation is verified in the wind tunnel test. In the heaving-pitching coupled motion, the results show that the nonlinear characteristics of aerodynamic forces, especially the aerodynamic moment, are mainly affected by the pitching motion. The phenomenon of high-order harmonic energy transfer is observed with the increase in pitching amplitude, and the main component of high-order harmonic can be determined by the pitching amplitude. The contribution of heaving motion to aerodynamic forces nonlinear components is small, but its influence on nonlinear characteristics is complex. Small amplitude heaving motion plays a positive damping role in heaving-pitching coupled motion, and its scope and effect of positive damping action are affected by pitching motion. The extreme value heaving amplitude of positive damping action is observed in the aerodynamic lift.

Computational Validation, Verification, and Stability Analysis of Ring-slot and Flat Circular Parachutes

Abstract: This paper describes a computational aerodynamics study of the drag and stability characteristics of rigid extraction parachute models. Computational fluid dynamics (CFD) simulations were conducted for both a 20% geometric porosity ring-slot canopy (20P RS) and 0% geometric porosity canopy (0P RS) in freestream conditions. The primary purpose of these simulations was to verify and validate simulations with the 20P RS and 0P RS canopies, thus creating increased confidence in the accuracy of extraction parachute CFD for future implementations as a part of the analysis for the Heavy Equipment Large Low Velocity AirDrop System (HELLVADS). Variation in Newton sub-iterations between three and five was conducted to determine the effect on temporal accuracy for verification of parachute aerodynamics with theoretical expectations. Validation of these CFD simulations was carried out through comparison of computational results to that of experimental results for similar rigid parachute models. Simulations predicted that the minimum number of Newton sub-iterations required for verification was five. Validation of drag coefficient for the 20P RS canopy was achieved, along with verification of lift and pitching moment coefficients at zero and five degrees angle of attack (AoA). Validation of drag coefficient for the 0P RS canopy was also achieved at 0°AoA, and verification data was also collected.