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Impulsive Loading Noise of a Lift-Offset Coaxial Rotor in High-Speed Forward Flight

AIAA JOURNAL 2020年第2期58卷 687-701页

作者： Jia, Zhongqi Lee, Seongkyu Univ Calif Davis Dept Mech & Aerosp Engn Davis CA 95616 USA

This study was conducted to investigate the impulsive acoustic characteristics of a lift-offset coaxial rotor in high-speed forward flight, as well as the impact of wake-grid resolution and turbulence modeling on acoustic prediction. High-fidelity computational fluid dynamics/computational structural dynamics loose-coupling simulations were performed for air-load prediction using the high-fidelity rotorcraft aeromechanics simulation software Helios, and impulsive loading noise was simulated using the acoustic prediction software PSU-WOPWOP at eight microphones positioned below the lower rotor plane. No significant discrepancy in air-load and acoustic predictions was found between the three turbulence modeling cases [Spalart-Allmaras (SA)-Reynolds-averaged Navier-Stokes, SA-detached-eddy simulation, and SA-delayed-detached-eddy simulation] with Delta finest=10%Ctip. It was found that the Delta finest=10%Ctip case showed a good convergence of impulsive loading noise at most microphones in terms of the wake-grid resolution. Isolated rotor simulations were also carried out to quantify the relative importance of the two impulsive loading-noise sources of a lift-offset coaxial rotor: self-blade-vortex interaction (BVI) and blade-crossover events. Contours of induced inflow ratio on the rotor disks revealed higher induced velocity for the lift-offset coaxial rotor than the isolated rotors. The higher induced flow ratio reduced the distribution of sectional normal force, strength of self-BVIs, and BVI noise of the lift-offset coaxial rotor. Even with the reduced BVI noise, the lift-offset coaxial rotor showed a dramatically higher impulsive sound-pressure level than the isolated rotors, especially at high speed, as a consequence of mainly blade-crossover events.

关键词： Rotorcraft Simulations Blade Vortex Interaction Detached Eddy Simulation Freestream Mach Number Turbulence Models Reynolds Averaged Navier Stokes computational structural dynamics Sound Pressure Level Acoustic Simulation Aerodynamic Efficiency

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Automation Tools for Rotorcraft Analysis on High-Performance Computing Centers

Automation Tools for Rotorcraft Analysis on High-Performance...

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AIAA Science and Technology Forum and Exposition (AIAA SciTech)

作者： Haehnel, Robert B. Wissink, Andrew George, Glover Hardin, Deanna Fegyveresi, John US ARMY Engineer Res & Dev Ctr Cold Reg Res & Engn Lab Hanover NH 03755 USA US Army CCDC Aviat Missile Command Aviat Dev Directorate Moffett Field CA USA US ARMY Engineer Res & Dev Ctr Informat Technol Lab Vicksburg MS USA

ISBN: (数字)9781624105951

ISBN: (纸本)9781624105951

Rotorcraft aerodynamic calculations are computationally intensive and, to determine the performance characteristics for a single airframe (e.g., hover, forward flight), require calculations over a range of representative flight conditions. To obtain performance curves for hover and forward flight can take millions of computer hours. In addition to the computational effort, considerable person-hours are expended submitting, monitoring, and postprocessing the results for each evaluation point. In this effort, we have developed a new CREATE-AV Helios plugin that monitors convergence of rotor hub forces and moments and can be used to reduce computational expense needed to determine hover performance. Additionally, we demonstrate the use of Galaxy Simulation Builder (GSB), a workflow management tool that efficiently works with an HPC environment, to automate standard rotorcraft performance calculations using Helios, i.e., hover and forward flight performance, and streamline case management and postprocessing the results of these workflows. GSB is flexible for a variety of workflows, including the ensemble modeling capability included as an additional example here.

关键词： Rotorcraft Simulations High Performance Computing Galaxies Airframes Flight Performance Turbulence Models Drag Coefficient Reynolds Averaged Navier Stokes computational structural dynamics Separated Flows

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Aerodynamic Shape Optimization for Flutter/LCO based design using Coupled Adjoint

Aerodynamic Shape Optimization for Flutter/LCO based design ...

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AIAA Science and Technology Forum and Exposition (AIAA SciTech)

作者： Prasad, Rachit Cho, Seongim Virginia Polytech Inst & State Univ Aerosp & Ocean Engn Dept Blacksburg VA 24060 USA Virginia Polytech Inst & State Univ Aerosp & Ocean Engn Blacksburg VA 24060 USA

ISBN: (数字)9781624105951

ISBN: (纸本)9781624105951

When designing aircraft wings shapes, it is important to ensure that the flight envelope does not overlap with regions of flutter or Limit Cycle Oscillation (LCO). A quick assessment of this condition for various design candidates is key to successful design. For this, sensitivity of the flutter velocity needs to be known with the respect of design parameters. The conventional approach of computing this sensitivity has been to differentiate the eigenvalues of the aero-structural system. However, such technique is only applicable for linear or linearized models and cannot be applied to systems undergoing LCO or other nonlinear effects. Though high fidelity CFD modeling can be implemented to overcome this problem for aerodynamic nonlinearities, the method becomes prohibitively expensive, as it requires time accurate calculations. Same goes for computing its sensitivity with respect to design variables. In this work, the time spectral method has been used to compute conditions for both flutter onset, LCOs and their design sensitivities in a computationally efficient way. One of the advantages of the time spectral based formulation is the computational efficiency obtained by eliminating transient flow solutions to reach a periodic steady state, through the solution approximation of a discrete Fourier series. Also, the time spectral form of the governing equation facilitates the application of steady form of adjoint sensitivity analysis for dynamic problems. Large memory and computational cost requirements of unsteady adjoint sensitivity analysis are circumvented by using the periodic steady state formulation. In this paper, steady adjoint formulation for time spectral method based flutter/LCO prediction has been implemented and used to carry out aerodynamic shape optimization for a two DOF flutter model with NACA 64010A airfoil cross section. The objective function has been to maximize with LCO velocity with bounds on the bump function coefficients.

关键词： Aerodynamic Shape Optimization Airfoil computational Fluid dynamics Sensitivity Analysis Computing structural System Flight Envelope Nonlinear Aeroelastic Systems Fluid Structure Interaction computational structural dynamics

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CFD/CSD Study of Interactional Aerodynamics of a Coaxial Compound Helicopter in High-Speed Forward Flight

CFD/CSD Study of Interactional Aerodynamics of a Coaxial Com...

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AIAA Science and Technology Forum and Exposition (AIAA SciTech)

作者： Klimchenko, Vera Baeder, James Univ Maryland Dept Aerosp Engn College Pk MD 20740 USA

ISBN: (数字)9781624105951

ISBN: (纸本)9781624105951

A computational study was conducted to investigate the aerodynamic interactions between various components of a compound coaxial helicopter, using a full vehicle CFD/CSD coupling methodology. A notional X2TD helicopter consisting of a coaxial rotor, airframe and an aft-mounted propeller, was modeled in this study. A high-fidelity computational fluid dynamics framework, HPCMP CREATE(TM)-AV Helios, was used in conjunction with an in-house computational structural dynamics solver, to simulate the helicopter in steady forward flight. A full vehicle coupling methodology was implemented to correct the low fidelity aerodynamic model of main rotor blades and airframe, within the structural solver. Rotor blade sectional airloads, mean propulsor power and time-averaged fuselage airloads were transferred to the structural solver during each coupling iteration. Efforts were made to identify and analyze effects of full vehicle CFD/CSD coupling methodology on rotor trim variables. The aerodynamic interactions between various components of the vehicle were also investigated.

关键词： Helicopter Rotor computational Fluid dynamics computational structural dynamics Interactional Aerodynamics Airframes Propellers Coaxial Rotor Rotor Blades Yaw Aerodynamic Performance

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A Numerical Investigation of Parachute Deployment in Supersonic Flow

A Numerical Investigation of Parachute Deployment in Superso...

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AIAA Science and Technology Forum and Exposition (AIAA SciTech)

作者： Boustani, Jonathan Anugrah, Gokul Barad, Michael F. Kiris, Cetin C. Brehm, Christoph Univ Kentucky Dept Mech Engn Lexington KY 40506 USA NASA Ames Res Ctr Computat Aerosci Branch Moffett Field CA 94035 USA

ISBN: (数字)9781624105951

ISBN: (纸本)9781624105951

A validated computational fluid-structure interaction method applied to supersonic parachute inflation is extended to consider a unique, parallel self-contact algorithm, porosity interface conditions on the canopy, improved flow field sampling procedures for obtaining quality loading on the parachute canopy, adaptive mesh refinement, and improved treatment of thin geometries in an immersed boundary framework. These extensions are discussed in detail and demonstrated individually on test problems. Finally, the developments are brought together for demonstration on a sub-scale MSL parachute geometry.

关键词： Compressible Flow computational Fluid Structure Interaction Adaptive Mesh Refinement computational structural dynamics computational Fluid dynamics Free Stream Velocity Bow Shock Navier Stokes Equations Stress Distribution Permeability

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Multifield Variational Sectional Analysis for Accurate Stress Computation of Multilayered Composite Beams

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AIAA JOURNAL 2019年第4期57卷 1702-1714页

作者： Dhadwal, Manoj Kumar Jung, Sung Nam Konkuk Univ Dept Aerosp Informat Engn Seoul 05029 South Korea

A multifield variational beam sectional analysis is proposed based on the Hellinger-Reissner principle for anisotropic beams with arbitrary cross-sectional geometries and material distributions. Both stresses and three-dimensional (3D) warping deformations are treated as unknowns, which are modeled using the isoparametric finite element (FE) shape functions. The nodal stresses are solved on each material domain, resulting in the required continuity within the domain and discontinuity at the material interfaces. A generalized Timoshenko-like stiffness matrix is constituted from the 3D warping solution inherently describing Timoshenko model for transverse shear, Poisson deformations, and associated couplings. The accuracy of the present analysis is demonstrated for benchmark composite beams with elastic couplings. The computed elastostatic responses are in excellent agreement with those of 3D FE analysis and experimental data. The stress predictions from the present multifield formulation show excellent correlation with 3D FE results using fewer elements in comparison to the conventional displacement-based approach while maintaining the stress continuity requirements for multilayered composite beams.

关键词： Interlaminar Stress Stiffness Matrices Lagrange Multipliers Material Properties structural Optimization Bending Moment Nastran computational structural dynamics computational Fluid dynamics Cantilever Beam

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Numerical Simulation of Horizontal Axis Wind Turbines with Vortex Generators

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INTERNATIONAL JOURNAL OF AERONAUTICAL AND SPACE SCIENCES 2019年第2期20卷 325-334页

作者： Lee, Hak Min Kwon, Oh Joon Korea Adv Inst Sci & Technol Dept Aerosp Engn Daejeon 34141 South Korea

In the present study, a simulation about the effects of vortex generators on horizontal axis wind turbine rotor blade was numerically conducted using a static coupled CFD-CSD method. A Navier-Stokes CFD flow solver based on unstructured meshes was used to obtain the blade aerodynamic loads. A FEM-based CSD solver employing a nonlinear coupled flap-lag-torsion beam theory was utilized to calculate the blade elastic deformation. The coupling of the CFD and CSD solvers was accomplished in a loosely coupled manner by exchanging the information between the two solvers at infrequent intervals. The static coupled CFD-CSD method was applied to the NREL 5MW reference wind turbine rotor under steady axial flow conditions. Triangular counter-rotating vortex generators were adopted to control flow separation and radial flow in the inboard section of the NREL 5MW reference rotor blades. They were installed on the inboard part of the blade from 0.2 to 0.4R. As a result of the flow analysis considering the counter-rotating vortex generators, strong vortices were generated by counter-rotating vortex generators. It can be seen that the regions where flow separation and radial flow occur in the inboard sections were reduced compared to the baseline wind turbine. For this reason, the maximum power improvement due to counter-rotating vortex generators was 1.04% at the rated wind speed.

关键词： computational fluid dynamics computational structural dynamics Horizontal axis wind turbine Vortex generators

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Nonlinear Airfoil Limit Cycle Analysis Using Continuation Method and Filtered Impulse Function

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AIAA JOURNAL 2020年第5期58卷 1976-1991页

作者： Yu, Q. Damodaran, M. Khoo, B. C. Natl Univ Singapore Singapore 119077 Singapore Natl Univ Singapore Ctr Flight Sci Singapore 119077 Singapore Natl Univ Singapore Temasek Labs Singapore 119077 Singapore Dept Mech Engn Block EA9 Engn Dr 1 Singapore 117575 Singapore Temasek Labs T Lab Bldg5A Engn Dr 1 Singapore 117411 Singapore

In this study, an adaptive step size control algorithm incorporated in the continuation method (CM) is developed and combined with the filtered impulse function method based on aerostructural solvers and applied to two aeroelastic analysis tasks concerned with modes tracking and parameter variation. The nonlinear limit cycle oscillation (LCO) of a NACA0012 airfoil with control surface free-play behavior is considered to illustrate how this adaptive step can achieve a balance between the stability, accuracy, and efficiency in the modes crossing region in modes tracking, the flutter point region in modes tracking, and the detrimental LCO region in parameter variation. It is shown that the computation time for modes tracking using this approach can be reduced by more than 65% while achieving almost the same estimate of the flutter speed as when using a fixed step size. The study also addresses a few unique and important phenomena in parameter variation such as modes jumping in the LCO curve that occur frequently using this adaptive step size algorithm. Furthermore, a combination of the modes tracking results to provide an estimate for the restart point for the CM solver to overcome the occurrence of possible extraneous solutions or divergence is proposed. The results of flutter analysis for linear structural system and nonlinear LCO analysis are validated against the results from experiments and the classical Theodorsen theory. The effect of viscous damping on the occurrence of detrimental LCO phenomena is also discussed and compared with the corresponding nondamping cases.

关键词： Airfoil Aeroelastic Stability Viscous Damping computational structural dynamics Control Algorithm structural System CFD Simulation Airspeed Influence Coefficients Lift Coefficient

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Local Finite Element Refinement for Accurate Dynamic Stress via Modal Information Only

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AIAA JOURNAL 2020年第8期58卷 3593-3606页

作者： Zhou, Yadong Nanjing Univ Aeronaut & Astronaut Coll Civil Aviat 29 Jiangjun Ave Nanjing 211100 Peoples R China

Accurate stress responses are the basics for failure analysis of aerospace structures, but they still can be challenging in numerical simulations for dynamic systems. This work exploits the stress mode shapes (SMSs) in local finite element (FE) refinement for the purpose of accurate dynamic stress estimation. Toward structural FE modeling, identification of critical locations via predominant SMSs is theoretically demonstrated. To pursue more accurate dynamic stress, a strategy for local FE refinement is proposed by using the information from stress modal analysis. The strategy involves a two-step procedure. First, modal participation factors (MPFs) are used to extract the predominant modes. Second, retained SMSs are evaluated for the local remeshing. Numerical simulations of a representative thin plate with geometric details were conducted. The SMSs were investigated in detail. Together with MPFs, SMSs can help to localize the dangerous stresses and then refine the local meshes to accurately calculate stress responses. By taking full advantage of numerically obtained SMSs, local structural FE modeling can be applied in a straightforward way with high efficiency. Results indicate that SMSs can reveal the underlying mechanism that governs the overall dynamic stress response.

关键词： Dynamic Displacements Stress Concentration Numerical Simulation Frequency Response Functions Model Order Reduction computational structural dynamics Vibration Fatigue Stiffness Matrices Poisson's Ratio Beam (Structures)

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UH-60A Rotor Analysis with an Accurate Dual-Formulation Hybrid Aeroelastic Methodology

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JOURNAL OF AIRCRAFT 2020年第1期57卷 113-127页

作者： Wilbur, Isaac C. Moushegian, Alex Smith, Marilyn J. Whitehouse, Glen R. Georgia Inst Technol Sch Aerosp Engn Atlanta GA 30332 USA Continuum Dynam Inc Ewing NJ 08618 USA

Dual-solver hybrid methodologies that couple fluid solvers in different regions of the flowfield have been developed to accelerate convergence with minimal compromises in accuracy. A new dual-solver hybrid analysis framework that addresses some of the major shortcomings of prior dual-solver hybrid methodologies has been developed through an academic-industry partnership. In this effort, one of the hybrid solvers, comprising of a computational fluid dynamics-computational structural dynamics (CFD-CSD) solver coupled with a Lagrangian wake-panel module, is assessed. The hybrid solver's ability to replicate the accuracy of the more expensive CFD-CSD approach and its ability to capture the physics of the rotor system are presented. The criteria that have been evaluated include integrated aerodynamic performance quantities, structural loads and moments, and near-body wakes. If the best practices extracted from this analysis are applied, the analysis with a reduced off-body CFD mesh is able to predict forward-flight rotor behavior that is within 4% of a full CFD simulation with up to 70% cost savings. This accuracy has been assessed on both high-speed and high-thrust flight conditions and has been quantitatively verified for aerodynamic, structural, and hub variables of interest at a number of radial blade stations for a frequency range of 0-16/rev.

关键词： Detached Eddy Simulation structural Load computational structural dynamics Aerodynamic Performance Rotor Systems Aerodynamic Coefficients Reynolds Averaged Navier Stokes Vortex Filaments Turbulence Models Rotor Wake

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