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5th Joint ASME/JSME Fluids Engineering Summer Conference

作者： Zhang, Sijun ESI CFD Inc Huntsville AL 35806 USA

ISBN: (纸本)9780791842881

A flexible robust method Coupling computational fluid dynamics (CFD) and computational structural dynamics (CSD) is developed for the general applications of aeroelastic analyses. This coupling is achieved through a Multi-Disciplinary Computing Environment (MDICE), which allows several computer codes of 'modules' to communicate in a highly efficient fashion. The present approach offers the advantage of utilizing well-established single-disciplinary codes in a multi-disciplinary framework. The flow solver is density-based for modeling compressible, turbulent flow problems using structured and/or unstructured grids. A modal approach is employed for the structural response. The flow and structural solvers are fully coupled via successive iterations within each physical time step. Three aeroelastic cases were analyzed with the proposed method;they are steady flow/modal analysis of an AGARD 445 wing, transient flow/modal analysis of the AGARD 445 wing, and vertical tail buffeting of F/A- IS.

关键词： aeroelastic fluid structure interaction time-accurate solution computational fluid dynamics computational structural dynamics

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Rotor airloads prediction using loose aerodynamic/structural coupling

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JOURNAL OF AIRCRAFT 2006年第3期43卷 732-742页

作者： Potsdam, Mark yeo, Hnsoo Yeo Johnson, Wayne NASA Ames Res Ctr USA Res Dev & Engn Command Moffett Field CA 94035 USA

A computational fluid dynamics (CFD) code and rotorcraft computational structural dynamics (CSD) code are coupled to calculate helicopter rotor airloads across a range of flight conditions. An iterative loose (weak) coupling methodology is used to couple the CFD and CSD codes on a per revolution, periodic basis. The CFD code uses a high fidelity, Navier-Stokes, overset grid methodology with first principles-based wake capturing. Modifications are made to the CFD code for the aeroelastic analysis. For a UH-60A Blackhawk helicopter, three challenging level flight conditions are computed: 1) high speed, mu = 0.37, with advancing blade negative lift, 2) low speed, mu = 0.15, with blade-vortex interaction, and 3) high thrust with dynamic stall, mu = 0.24. Results are compared with UH-60A Airloads program flight test data. For all cases the loose coupling methodology is shown to be stable, convergent, and robust with full coupling of normal force, pitching moment, and chord force. In comparison with flight test data, normal force and pitching moment phase and magnitude are in good agreement. The shapes of the airloads curves are well captured. Overall, the results are a noteworthy improvement over lifting line aerodynamics used in rotorcraft comprehensive codes.

关键词： Freestream Mach Number CFD Flight Testing Blade Vortex Interaction computational structural dynamics Rotor Wake Helicopter Rotor Level Flight CFD Codes Aeroelastic Analysis

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A transient response analysis in the state-space applying the average velocity concept

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JOURNAL OF SOUND AND VIBRATION 2005年第3-5期281卷 1023-1035页

作者： Kim, BO Lee, AS Korea Inst Machinery & Mat Rotor Dynam Grp Taejon 305600 South Korea

An implicit direct-time integration method for obtaining transient responses of general dynamic systems is described. The conventional Newmark method cannot be directly applied to state-space first-order differential equations, which contain no explicit acceleration terms. The method proposed here is the state-space Newmark method that incorporates the average velocity concept;and can be applied to an analysis of general dynamic systems that are expressed by state-space first-order differential equations. It is also readily coded into a program. Stability and accuracy analyses indicate that the method is numerically unconditionally stable like the conventional Newmark method, and has a period error of second-order accuracy for small damping and fourth-order for large damping and an amplitude error of second-order, regardless of damping. In addition, its utility and validity are confirmed by two application examples. The results suggest that the proposed state-space Newmark method based on average velocity be generally applied to the analysis of transient responses of general dynamic systems with a high degree of reliability with respect to stability and accuracy. (C) 2004 Elsevier Ltd. All rights reserved.

关键词： computational structural dynamics TIME-INTEGRATION METHODS HIGHER-ORDERACCURATE STEP INTEGRATION SMAC TECHNIQUES ALGORITHMS STABILITY NEWMARK

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Aeroelastic calculations for the Hawk aircraft using the Euler equations

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JOURNAL OF AIRCRAFT 2005年第4期42卷 1005-1012页

作者： Woodgate, MA Badcock, KJ Rampurawala, AM Richards, BE Nardini, D Henshaw, AJD Univ Glasgow Computat Fluid Dynam Lab Dept Aerosp Engn Glasgow G12 8QQ Lanark Scotland BAE Syst Aerodynam Technol Brough HU15 1EQ England

This paper demonstrates coupled time-domain computational-fluid-dynamics (CFD) and computational-structural-dynamics simulations for flutter analysis of a real aircraft in the transonic regime. It is shown that a major consideration for a certain class of structural models is the transformation method, which is used to pass information between the fluid and structural grids. The aircraft used for the calculations is the BAE Systems Hawk. A structural model, which has been developed by BAE Systems for simplified linear flutter calculations, only has a requirement for O(10) degrees of freedom. There is a significant mismatch between this and the surface grid on which loads and deflections are defined in the CFD calculation. This paper extends the constant volume tetrahedron tranformation, previously demonstrated for wing-only aeroelastic calculations, to multicomponent, or full aircraft, cases and demonstrates this for the Hawk. A comparison is made with the predictions of a linear flutter code.

关键词： Aircrafts Euler Equations Vortex Lattice Method structural Modeling computational structural dynamics BAE Systems Fuselages Freestream Mach Number Reynolds Averaged Navier Stokes Wing Root

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Application of the arc-length method in nonlinear frequency response

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JOURNAL OF SOUND AND VIBRATION 2005年第1-2期284卷 133-149页

作者： Ferreira, JV Serpa, AL Univ Estadual Campinas Fac Mech Engn Dept Computat Mech BR-13083970 Campinas SP Brazil

Several iterative numerical techniques have been developed to solve nonlinear structural problems and some of these methods are capable to trace complex paths in the space load/displacement. One of those most popular procedures is the arc-length method of Crisfield, which possesses the capability to overcome inflection points, without having the necessity of determining them. A great similarity exists between curves of the nonlinear load/displacement path obtained with the arc-length method, and curves of the frequency response of nonlinear dynamic systems. Both curves present limit points with snap-back and snap-through phenomena. This work consists of the description and the application of the arc-length method to solve a system of nonlinear equations obtaining as a result the nonlinear frequency response. The analysis employs the concept of the describing functions where the fundamental harmonic component is considered the most relevant and for some cases can be considered an approximation to the effect of all harmonics. Some examples involving a cubic stiffness and a gap nonlinearity are employed to illustrate the methodology. (c) 2004 Elsevier Ltd. All rights reserved.

关键词： computational structural dynamics FINITE-ELEMENT EQUATIONS TIME-INTEGRATIONMETHODS VIBRATION SYSTEMS

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Direct aeroelastic bifurcation analysis of a symmetric wing based on Euler equations

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JOURNAL OF AIRCRAFT 2005年第3期42卷 731-737页

作者： Badcock, KJ Woodgate, MA Richards, BE Univ Glasgow Dept Aerosp Engn Fluid Dynam Lab Glasgow G12 8QQ Lanark Scotland Univ Glasgow Dept Aerosp Engn Computat Fluid Dynam Lab Glasgow G12 8QQ Lanark Scotland

The application of a sparse matrix solver for the direct calculation of Hopf bifurcation points for the flexible AGARD 445.6 wing in a transonic flow modeled using computational fluid dynamics is considered. The iteration scheme for solving the Hopf equations is based on a modified Newton's method. Direct solution of the linear system for the updates has previously been restrictive for application of the method, and the sparse solver overcomes this limitation. Previous work has demonstrated the scheme for aerofoil calculations. The current paper gives the first three-dimensional results with the method, showing that an entire flutter boundary for the AGARD 445.6 wing can be traced out in a time comparable to that required for a small number of time-marching calculations, yielding two orders of magnitude improvement when compared to the time-marching approach.

关键词： Euler Equations Aerofoil Riemann Solver Implicit Methods Transonic Flow Freestream Velocity computational structural dynamics Finite Element Modeling structural Simulation Reynolds Averaged Navier Stokes

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Nonlinear aeroelastic computations of a wing/pylon/finned-store using parallel computing

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AIAA JOURNAL 2005年第1期43卷 53-62页

作者： Kim, DH Park, YM Lee, I Kwon, OJ Gyeongsang Natl Univ Sch Mech & Aerosp Engn Jinju 660701 South Korea Korea Aerosp Res Inst Aerodyman Div Taejon 305333 South Korea Korea Adv Inst Sci & Technol Dept Aerosp Engn Taejon 305701 South Korea

Nonlinear aeroelastic computations are presented for a sweptback wing with underpylon/finned-store in the transonic and supersonic flow regions, where strong shock wave interactions exist. A modal-based coupled nonlinear aeroelastic analysis system with the matched-point concept has been developed using the high-speed parallel processing technique. Advanced numerical techniques such as computational structural dynamics and computational fluid dynamics are used. It is expected to provide accurate and useful engineering data in the aeroelastic and structural design of flight vehicles. For the nonlinear unsteady aerodynamics in high transonic flow region, Euler equations based on an unstructured grid system have been applied to consider fully the complex geometries. Linear and nonlinear aeroelastic computations have been conducted and are compared for the transonic and supersonic flow regions. Typically, it is shown that the advanced numerical approach gives much more conservative flutter boundary for the wing/pylon/store model than those predicted by the classical linear aerodynamic theories for high transonic flow. Also, important results indicate that in transonic flow the critical nonlinear flutter or limit-cycle oscillation-like phenomenon may be dominantly induced or within the bounds of strong possibility due to the shock coupling effect of unstable store induced vibration.

关键词： Parallel Computing Aerodynamic Flows computational structural dynamics FLUENT Aeroelastic Stability Transonic Aircraft Euler Equations Unstructured Grid Shock Wave Interaction Sweptback Wings

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Reduced-order-model approach for aeroelastic analysis involving aerodynamic and structural nonlinearities

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AIAA JOURNAL 2005年第3期43卷 560-571页

作者： Munteanu, S Rajadas, J Nam, C Chattopadhyay, A Arizona State Univ Dept Aerosp & Mech Engn Tempe AZ 85225 USA Arizona State Univ Mech & Mfg Engn Technol Dept Tempe AZ 85225 USA

A reduced-order model (ROM) for solving an aeroelasticity problem including structural and aerodynamic nonlinearities is introduced. The aerodynamic system is identified using a Volterra-based ROM. The appropriate procedures needed for the identification of the aerodynamic linearized kernel are presented, and a procedure to identify the first- and second-order Volterra kernels and a linearized ROM kernel from aerodynamic step response is detailed. A coupled framework for addressing the nonlinear aeroelasticity problem using a typical wing section model is introduced for the validation of the procedure. Nonlinear unsteady aerodynamic forces in both subsonic and transonic regimes are evaluated using a conventional approach using the CFL3D (version 6.1) code capable of integrating Navier-Stokes and the structural equations. The computational-fluid-dynamics (CFD) solver is used to compute the aerodynamic response to step or impulse inputs. Aerodynamic responses to arbitrary inputs are predicted using ROM kernels. The Gaussian pulse response obtained using ROM was validated by comparison with the response obtained from CFD solver. Aeroelastic analysis was conducted using the ROM with aerodynamic and structural nonlinearities. The results show that the reduced-order model can estimate accurately flutter speed as well as the limit-cycle oscillations (LCO). Also the ROM approach is found to be computationally efficient.

关键词： structural Nonlinearities Nonlinear Aeroelasticity CFD Aerodynamic Force Vector CFL3D Transient Response Nonlinear Systems Dynamic Pressure computational structural dynamics Navier Stokes Equations

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Restricted Pade scheme in computational structural dynamics

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COMPUTERS & STRUCTURES 2001年第20-21期79卷 1913-1921页

作者： Ruge, P Tech Univ Dresden Fak Bauingenieurwesen Dynam Tragwerke D-01062 Dresden Germany

Restricted Pade schemes R-mp where the denominator is a complete power p of a linear function have been examined analytically by Norsett. Here this method is evaluated with paying special attention to numerical aspects when solving typical finite-element systems in structural dynamics with n degrees of freedom and with essential properties like sparsety and symmetry, This paper presents an efficient implicit restricted time-stepping scheme R-22 with a final coefficient matrix of order n and a leading error term proportional to h(4). This is a significant improvement compared with the most popular Pade- P-11-Newmark scheme with matrix order n, too, but error term h(3) on the one hand and the well established Pade-P-12-discontinuous Hamiltonian approach with error term h(4) but matrix order 2 x n on the other hand. The classical P-11-scheme and the new restricted R-22-scheme are compared in a modal manner and by assessing the correlation between local error estimator and global error. (C) 2001 Published by Elsevier Science Ltd.

关键词： time-finite elements Pade schemes error estimation time-step control modal assessment computational structural dynamics

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Oscillatory blowing control numerical simulation of airfoil flutter by high-accuracy method

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JOURNAL OF AIRCRAFT 2004年第3期41卷 610-615页

作者： Yan, J Xin, Y Tsing Hua Univ Beijing 100084 Peoples R China

It is known that oscillatory blowing can be used to delay flow separation and stall. The oscillatory blowing technique is applied to control of the airfoil's flutter. A high accuracy fluid-structure coupling numerical method is used. The numerical results show that the steady blowing will weaken the flutter. However, the excess blowing will decrease the lift coefficient. The best blowing velocity can be found by the present numerical method. The influence of the frequency of the oscillatory blowing on the airfoil's vibration is also studied. The numerical results show that the oscillatory blowing is more efficient than steady blowing.

关键词： Airfoil Flutter computational Fluid dynamics Lift Coefficient Boundary Layer Separation Freestream Mach Number Vortex Shedding Stall Flutter Turbulence Models Navier Stokes Equations computational structural dynamics

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