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Coupled Aeroelastic Study of a Flexible Micro Air Vehicle-Scale Flapping Wing in Hovering Flight

JOURNAL OF AIRCRAFT 2022年第1期59卷 154-172页

作者： Lankford, James L. Chopra, Inderjit Univ Maryland Dept Aerosp Engn College Pk MD 20742 USA Univ Maryland College Pk MD 20742 USA

Instantaneous force and structural deformation experiments were performed on a flexible, structurally characterized, low-aspect-ratio representative flapping wing. A six-component force balance was used to measure aerodynamic-force time history over a flap cycle. A VICON motion capture setup tracked the wing deformations while flapping. Measured aerodynamic forces and wing deformations were compared against coupled computational fluid dynamics/computational structural dynamics (CFD/CSD) aeroelastic analysis results. The CFD solver is an unsteady Reynolds-averaged Navier-Stokes solver. The CSD solver is a general-purpose multibody dynamics solver capable of modeling geometrically nonlinear beam and shell elements. The CFD/CSD results were able to capture the overall trend in aerodynamic forces and wing deformations. Although predicted and measured variations in lift were similar, the drag-force magnitudes tended to be underpredicted by the coupled aeroelastic solver. The coupled CFD/CSD solver was used to evaluate the influence of wing flexibility on wing performance. Results showed that, in particular instances, decreasing wing stiffness increased the time-averaged aerodynamic lift and lift-to-power ratio. Decreased wing stiffness led to reduced leading-edge vortex circulation strength. This suggests that the increased wing performance is mainly due to a redirection of the resultant force vector allowed by the increased wing compliance.

关键词： Flapping Frequency Micro Air Vehicle Aerodynamic Coefficients CFD Simulation computational structural dynamics Aeroelastic Analysis Reynolds Averaged Navier Stokes Aspect Ratio Vortices Multibody dynamics

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Blade Vibration and Its Effect on the Optimal Performance of Helicopter Rotors

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JOURNAL OF AIRCRAFT 2022年第1期59卷 184-195页

作者： Tedesco, Matthew B. Hall, Kenneth C. Duke Univ Dept Mech Engn & Mat Sci Durham NC 27708 USA

In this paper, we develop a computationally efficient frequency-domain model that can be used to compute the required shaft power and vibratory loads for a trimmed helicopter rotor with flexible blades in forward flight. The aerodynamic forces and power are modeled using a vortex-lattice method. A finite element model based on the linearized form of the Hodges-Dowell rotating beam equations is used to model the vibrating blades. Guyan reduction and harmonic balance are used to reduce the number of degrees of freedom. The model is validated against several previous computational and experimental models, with generally good agreement. For rotors that use higher harmonic control, the problem of minimizing the required power and/or vibratory loads is cast as a quadratic programming problem requiring a single linear matrix solve to find the optimum. We show that for moderate and high advance ratios, higher harmonic control can substantially reduce vertical hub forces, but only with an increase in required cruise power. For example, using four-per-revolution higher harmonic control, the vertical vibratory loads on the four-bladed HART II rotor can be decreased by about 30% for a 3.0% increase in induced power for at a forward flight advance ratio of 0.45.

关键词： Helicopter Rotor Finite Element Analysis computational structural dynamics Rotor Aerodynamics Quadratic Programming Vortex Lattice Method Frequency Domain Wake Vortices Blade Pitch Control Rotor Blades

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The effect of the tower's modeling on the aero-elastic response of the NREL 5 MW wind turbine 8

The effect of the tower's modeling on the aero-elastic respo...

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8th Wake Conference

作者： Bernardi, Claudio Della Posta, Giacomo De Palma, Pietro Leonardi, Stefano Bernardoni, Federico Bernardini, Matteo Cherubini, Stefania Politecn Bari Dipartimento Meccan Matemat & Management Via Re David 200 Bari Italy Sapienza Univ Rome Dept Mech & Aerosp Engn Via Eudossiana 18 Rome Italy Univ Texas Dallas Dept Mech Engn Richardson TX 75083 USA

In this work, we aim at evaluating the aeroelastic response of the blades of a standalone NREL 5MW wind turbine by means of a high-fidelity fluid-structure interaction solver based on large-eddy simulation, and compare the results with those of engineeringfidelity methods based on the Blade Element Momentum (BEM) theory. For the latter, we use the software OpenFAST [1], which couples an aerodynamic solver based on the BEM theory with a solver of the blades' structural dynamics. Concerning the computational fluid dynamics (CFD) solver, the tower and nacelle are modeled by means of an immersed boundary method, whereas the aeroelastic rotor is modeled by an actuator line model coupled with a computational structural dynamics (CSD) solver representing the blades as rotating cantilever beams. A comparison of the CFD-CSD results with the corresponding ones obtained by OpenFAST shows that the predicted displacements at the blade tip remarkably differ between the two approaches in correspondence of the passages of the blades in front of the tower. Indeed, the interaction between the blades and the tower introduces a significant perturbation in the local aerodynamics that leads to a drop of the displacement at the tip of the blade and of the root reaction magnitude, which appear to be not accurately described by OpenFAST.

关键词： Aeroelasticity computational Fluid dynamics computational structural dynamics Actuator Line Model Blade Element Momentum CFD-CSD model NREL 5MW Wind Turbine

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Torque Analysis of IPMC Actuated Fin of a Micro Fish like Device using Two-Way Fluid Structure Interaction Approach

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INTERNATIONAL JOURNAL OF ENGINEERING RESEARCH IN AFRICA 2022年第1期59卷 25-38页

作者： Ul Haq, Mazhar Gang, Zhao Sun, Zhuang-Zhi Aftab, S. M. Harbin Engn Univ Dept Mech & Elect Engn Harbin 150001 Heilongjiang Peoples R China

In this paper, a numerical simulation of three dimensional model of IPMC actuated fin of a fish like micro device is presented using two-way fluid structure interaction approach. The device is towed by the surface vessel through a tow cable. Fin is acting as dorsal fin of the fish to control depth of the device and also acts as a stabiliser against its roll motion. Fin's displacement disturbs water flow streamlines around it, as a result velocity and pressure profile of fluid's domain changes around the actuated fin. As fin's position continuously changes throughout its actuation cycle, this makes it transient structural problem coupled with a fluid domain. Fin's displacement is received by the fluid and resulting fluid forces are received by the fin making it a two-way fluid structure interaction (FSI) problem. Such problems are solved by multi field numerical simulation approach. This multifield numerical simulation is performed in ANSYS WORKBENCH by coupling transient structural and Fluid Flow (CFX) analysis systems. It is desirous to determine the torque acting on the fin due to fluid forces through its actuation cycle by IPMC actuators. The objective of this study is to develop the methodology (two-way fluid structural interaction (FSI)) used to simulate the transient FSI response of the IPMC actuated fin, subjected to large displacement against different flow speeds. Efficacy of fin as depressor and riser is also required to be judged by monitoring the forces acting on wing in response to its displacement under IPMC actuation. Same approach is also applicable to the self-propelled systems.

关键词： Numerical simulation Fluid structure interaction Ionic polymer metal composite computational structural dynamics computational fluid dynamics

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Active Manifold and Model-Order Reduction to Accelerate Multidisciplinary Analysis and Optimization

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AIAA JOURNAL 2021年第11期59卷 4739-4753页

作者： Boncoraglio, Gabriele Farhat, Charbel Stanford Univ Dept Aeronaut & Astronaut Durand BldgRoom 224-2 Stanford CA 94305 USA Stanford Univ Dept Aeronaut & Astronaut Aircraft Struct Durand BldgRoom 257 Stanford CA 94305 USA

A computational framework is proposed for efficiently solving multidisciplinary analysis and optimization (MDAO) problems in a relatively high-dimensional design parameter space. It relies on projection-based reduced-order models (PROMs) and a new concept of an active manifold (AM) to mitigate the curse of dimensionality during the training of the PROMs. The AM is discovered using a deep convolutional autoencoder for dimensionality reduction: it is proposed as a superior alternative to the concept of active subspace whose capabilities are limited by the associated affine approximation. The computational framework also blends the concept of a global PROM as a surrogate model of a nonlinear partial differential equation (PDE)-based behavior function with that of a database of local, linear PROMs for approximating a linear PDE-based behavior function. It is demonstrated for the solution of a flexible instance of NASA's Common Research Model for transport aircraft, where the objective function pertains to aerodynamics, the constraint relates to flutter, and the design space contains 58 structural and shape parameters. The obtained results illustrate the potential of the AM concept for mitigating the aforementioned curse of dimensionality. They also demonstrate the feasibility of the proposed computational framework for realistic MDAO problems and its ability to reduce solution time.

关键词： Model Order Reduction Aerodynamic Configurations Transport Aircraft CFD Fuselages computational structural dynamics Greedy Algorithm Broyden Fletcher Goldfarb Shanno Damping Ratio structural Modeling

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On the Dispersion Mechanism of the Flutter Boundary of the AGARD 445.6 Wing

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AIAA JOURNAL 2021年第7期59卷 2657-2669页

作者： Gao, Chuanqiang Liu, Xi Zhang, Weiwei Northwestern Polytech Univ Sch Aeronaut Natl Key Lab Aerodynam Design & Res Xian 710072 Peoples R China Northwestern Polytech Univ Sch Aeronaut Xian 710072 Peoples R China

The variation in the flutter boundary of the AGARD 445.6 wing in transonic and low supersonic states is an unresolved issue in the field of aeroelasticity. This well-known variation phenomenon is mainly reflected in three aspects: 1) the discrepancy between the computational and the experimental results;2) the large dispersion of the computational results between different solvers;3) the sensitivity of calculated flutter boundary to many factors, such as computational fluid dynamics discretization scheme and spatial resolution. However, the root cause of this phenomenon is not clear yet. In this paper, the physical mechanism of the dispersion phenomenon is investigated in the case of M-infinity = 1.141 using the reduced-order model (ROM)-based aeroelastic analysis model. A dominant least stable flow mode, which has an important effect on the flutter characteristic, is captured by the ROM. The variation in the damping of this dominant flow mode significantly affects the flutter boundary or even changes the instability branch of the structural mode. By adjusting the aerodynamic damping of the dominant flow mode, the flutter boundary curve under the aerodynamic damping variation is predicted. When comparing with the available literature results, the scattered literature data fall around the predicted curve, which indicates that the sensitivity of the damping of the dominant flow mode is the root cause for the dispersion phenomenon of the flutter boundary.

关键词： Aerodynamic Coefficients Detached Eddy Simulation Aeroelastic Stability computational structural dynamics Angle of Attack Reynolds Averaged Navier Stokes Supersonic Flow Turbulence Models Sensitivity Analysis Wind Tunnel Models

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Three-Dimensional Strains on Twisted and Swept Composite Rotor Blades in Vacuum

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JOURNAL OF AIRCRAFT 2021年第1期58卷 1-16页

作者： Chi, Cheng Datta, Anubhav Chopra, Inderjit Chen, Renliang Nanjing Univ Aeronaut & Astronaut Natl Key Lab Rotorcraft Aeromech Nanjing 210016 Peoples R China Univ Maryland Alfred Gessow Rotorcraft Ctr College Pk MD 20742 USA

This paper presents an investigation of the effects of tip sweep on highly twisted composite rotor blades by acquiring strain data in vacuum. Three parametric test cases were designed for strain measurements, and predictions from a special three-dimensional (3-D) finite element method were used for assessment of data. A set of rotating aluminum beams was also tested as a rudimentary baseline. Three sets of composite rotors (straight, twisted, and twisted-swept) were fabricated and tested, and blade properties carefully characterized. Prediction of 3-D strains was conducted using X3D, a 3-D multibody structural dynamic solver for rotor aeroelasticity. Comparison with measured strains showed overall satisfactory agreements. Under centrifugal loading, strong 3-D strain patterns were observed near the twisted-swept tip. The largest increase in strain magnitude is found to be caused by the twist. Evidence of strong lead-lag bending concentrations due to counteracting axial extension and localized in-plane shear were found in the twisted-swept tip.

关键词： Rotor Blades FEM Aeroelastic Stability Articulated Rotor Displacement Sensor Bending Stiffness Material Properties Computer Aided Design computational structural dynamics Strain Distribution

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Efficient computational Fluid dynamics Approach for Coaxial Rotor Simulations in Hover

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JOURNAL OF AIRCRAFT 2021年第1期58卷 197-202页

作者： Cornelius, Jason K. Schmitz, Sven Kinzel, Michael P. Penn State Univ Aerosp Engn University Pk PA 16802 USA Univ Cent Florida Mech & Aerosp Engn Orlando FL 32816 USA

A study is conducted to demonstrate a new computational fluid dynamics (CFD) methodology to quickly assess coaxial unmanned aerial systems (UASs). The approach retains a high-fidelity, three-dimensional, blade-resolved CFD evaluation of hovering rotorcraft. The method explores the mixing plane approach within STAR-CCM+ in application to coaxial rotorcraft in hover. These mixing planes are common for turbomachinery applications to coaxial rotorcraft in hover. These mixing planes are common for turbomachinery applications are well established. The study starts with discussing the niche where a mixing plane computational approach is relevant to coaxial rotorcraft in the context of conventional computational technologies. The development of the CFD model is discussed from the initial airfoil grid to the final coaxial rotor model.

关键词： Coaxial Rotor Detached Eddy Simulation Reynolds Averaged Navier Stokes Vortex Wake Helicopter Rotor Incompressible Flow Aspect Ratio Interactional Aerodynamics NACA 23012 computational structural dynamics

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Unsteady fabric vibration and the resulting wake velocity oscillations

Unsteady fabric vibration and the resulting wake velocity os...

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AIAA Aviation Forum and Exposition

作者： Shumway, Nathan M. US Air Force Acad Dept Aeronaut Colorado Springs CO 80840 USA

ISBN: (数字)9781624106101

ISBN: (纸本)9781624106101

Currently, the best methods for determining the performance of a parachute are full scale testing and coupled computational fluid dynamics-computational structural dynamics simulations (CFD-CSD). The easier option of the two is the CFD-CSD simulations, but there is currently no way to validate their ability to simulate parachutes, as there is a lack of detailed experimental data for parachute fabric. In order to provide such data, an experimental campaign has begun at the United States Air Force Academy to determine the optimal conditions at which to collect validation data. These experiments tested a piece of F111 nylon at a variety of flow speeds and angles of attack to determine a condition where the fabric regularly vibrates and a condition where the fabric is mostly static. The results indicate that the fabric will vibrate at higher flow speeds for all angles of attack and lower angles of attack at lower flow speeds. At lower speeds the vibrations are more regular whereas at higher speeds the fabric motion is more chaotic. Experiments to determine the influence of boundary conditions found that, when the leading edge of the fabric was unconstrained there were significantly higher amplitude vibrations at lower angles of attack. The same experiments indicated that the fabric does not vibrate significantly at angles close to stall, which is likely due to the non-linear stress-strain relationship for this fabric resulting in smaller changes in strain at higher stresses. The optimal condition for gathering data on predictable fabric motion was found to be at an angle of attack of 2 degrees at a low freestream velocity (< 15 m/s), and the best condition for a static validation test was determined to be an angle of attack between 10 degrees and 20 degrees also at a low freestream velocity.

关键词： Lift Coefficient Flexible Wings Freestream Velocity computational Fluid dynamics computational structural dynamics United States Air Force Flow Separation Aspect Ratio Low Speed Wind Tunnel Material Properties

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Active Manifold and Model Reduction for Multidisciplinary Analysis and Optimization

Active Manifold and Model Reduction for Multidisciplinary An...

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AIAA Science and Technology Forum and Exposition (AIAA SciTech Forum)

作者： Boncoraglio, Gabriele Farhat, Charbel Stanford Univ Dept Aeronaut & Astronaut Durand BldgRoom 2242 Stanford CA 94305 USA Stanford Univ Dept Aeronaut & Astronaut Aircraft Struct Durand BldgRoom 257 Stanford CA 94305 USA

ISBN: (数字)9781624106095

ISBN: (纸本)9781624106095

A computational framework is proposed for efficiently solving multidisciplinary analysis and optimization (MDAO) problems in a relatively high-dimensional design space. It relies on the appropriate blend of linear and nonlinear projection-based model order reduction to accelerate analysis and optimization;and on a new concept of nonlinear active manifold (AM) to mitigate the curse of dimensionality during the training of projection-based reduced-order models (PROMs). The method of AM relies on the nonlinear concept of a deep convolutional autoencoder for dimensionality reduction: it is proposed as a superior alternative to the concept of an active subspace whose capabilities are limited by the capabilities of an affine approximation. The proposed computational framework also blends the concept of a global PROM as a surrogate model of a discretized nonlinear partial differential equation (PDE)based behavior function with that of a database of local, linear PROMs for approximating, wherever appropriate, a linear PDE-based behavior function. Adaptive parameter sampling is performed for training the global, nonlinear PROM as well as for populating the database of local, linear PROMs. The proposed computational framework is demonstrated for the solution of an MDAO problem formulated for a flexible instance of NASA's Common Research Model, where the objective function pertains to aerodynamics in the transonic regime, the constraint relates to flutter, and the design space contains 58 structural and aerodynamic shape design variables. The obtained numerical results illustrate the potential of the AM method for addressing the curse of dimensionality. They also demonstrate the feasibility of the computational framework for realistic MDA Oproblems and highlight its potential for reducing solution time.

关键词： Model Order Reduction Aerodynamic Configurations computational Fluid dynamics Fuselages computational structural dynamics Greedy Algorithm structural Modeling Damping Ratio Optimization Algorithm Sweep Angle

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