Presented is a harmonic-balance computational fluid dynamic approach for modeling limit-cycle oscillation behavior of aeroelastic airfoil configurations in a viscous transonic flow. For the NLR 7301 airfoil configuration studied, accounting for viscous effects is shown to significantly influence computed limit-cycle oscillation trends when compared to an inviscid analysis. A methodology for accounting for changes in mean angle of attack during limit-cycle oscillation is also developed.

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Modeling Viscous Transonic Limit Cycle Oscillation Behavior Using a Harmonic Balance Approach

Transonic aeroelastic simulation for instability searches and uncertainty analysis

This paper considers the substitution of the computational-fluid-dynamics solver within an aerostructural coupling scheme by an efficient reduced-order surrogate model to realize high-fidelity nonlinear aeroelastic analyses within a fraction of the time compared to the corresponding coupled computational-fluid-dynamics analysis. The presented surrogate model approach is a combination of parameter reduction via proper orthogonal decomposition and system identification methods designed to cover nonlinear aerodynamic effects such as viscosity as well as transient effects. The investigated test case is the thick NLR7301 airfoil that shows significant nonlinear aerodynamic behavior along with nonnegligible viscous effects. The model is identified from a set of transient forced motion computational-fluid-dynamics analyses. After identification, the model is used to predict the discrete surface force distribution of the NLR7301 airfoil in static as well as transient coupled analyses. It is shown that the static ...

Efficient Surrogate Modelling of Nonlinear Aerodynamics in Aerostructural Coupling Schemes

The design of classic active flutter controllers has often been based on low-fidelity and low-accuracy linear aerodynamic models. Most of these models were usually treated as a linear time-invariant system, without considering time-varying parameters, such as the Mach number, the angle of attack, the Reynolds numbers, etc. A high-fidelity reduced-order model based on the proper orthogonal decomposition adaptation algorithm is used to develop a new general linear parameter-varying aeroservoelastic model with aerodynamic nonlinearity. A robust gain-scheduling control-law design method for active flutter suppression based on the proposed linear parametervarying model is investigated. The proposed design method is demonstrated with the Goland wing aeroelastic model. The simulation results show that the linear parameter-varying gain-scheduled controller can effectively suppress flutter over a range of airspeeds, and the flutter boundary in the transonic regime is simultaneously increased by nearly 20% to 30%.

Adaptive Reduced-Order-Model-Based Control-Law Design for Active Flutter Suppression

Active control for nonlinear aeroelastic structures is an attractive innovative technology. The design of classic active flutter controllers has often been based on low-fidelity and low-accuracy linear aerodynamic models. Multi-physics high-fidelity reduced order model (ROM) was used to design active control laws. In order to provide a lower-order model for controllers design, a balanced proper orthogonal decomposition ROM (POD-BT/ROM) was investigated. A state-space aeroservoelastic model and the active flutter suppression control law design method based on POD-BT/ROM were proposed. The effectiveness of the proposed method was then demonstrated by NACA 0012 airfoil, AGARD 445.6 wing and the Goland wing+ aeroelastic model.

Active flutter suppression control law design method based on balanced proper orthogonal decomposition reduced order model

As the amplitude of the unsteady flow oscillation is large or large changes occur in the mean background flow such as limit cycle oscillation, the traditional proper orthogonal decomposition reduced order model based on linearized time or frequency domain small disturbance solvers can not capture the main nonlinear features. A new nonlinear reduced order model based on the dynamically nonlinear flow equation was investigated. The nonlinear second order snapshot equation in the time domain for proper orthogonal decomposition basis construction was obtained from the Taylor series expansion of the flow solver. The NLR 7301 airfoil configuration and Goland+ wing/store aeroelastic model were used to validate the capability and efficiency of the new nonlinear reduced order model. The simulation results indicate that the proposed new reduced order model can capture the limit cycle oscillation of aeroelastic system very well, while the traditional proper orthogonal decomposition reduced order model will lose effectiveness.

A nonlinear POD reduced order model for limit cycle oscillation prediction

When the amplitude of the oscillation of the unsteady flow is large or there is large perturbation relative to the mean background flow, the traditional proper orthogonal decomposition/reduced order model (POD/ROM) based on linearized time or frequency domain small disturbance solvers cannot capture the main nonlinear features well such as limit cycle oscillation (LCO), which is very dangerous for the structure. Therefore, the traditional linear ROMs are not good enough for limit cycles prediction and active control law design. A new nonlinear ROM based on dynamically nonlinear flow equation NPOD/ROM was investigated. The nonlinear second-order snapshot equation in time domain for POD basis construction is obtained from the Taylor series expansion of the flow solver. The simulation results indicate that the NPOD/ROM can capture LCO very well and is also very convenient for active control law design, while the traditional POD/ROM lose effectiveness.

Gui-Rong Yan

Papers

A nonlinear POD reduced order model for limit cycle oscillation prediction

Limit cycle oscillation prediction and control design method for aeroelastic system based on new nonlinear reduced order model

A Nolinear POD Reduced Order Model for Limit Cycle Oscillation Prediction