16:00
Transonic aeroelasticity
Chair: Julian Seeley
16:00
30 mins
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Transonic limit cycle oscillations of the benchmark supercritical wing
Bret Stanford, Pawel Chwalowski, Kevin Jacobson
Abstract: This paper considers transonic flutter mechanisms of the Benchmark Supercritical Wing, a model under study in the Aeroelastic Prediction Workshop series. Flutter boundaries are mapped out across an angle-of-attack sweep at Mach 0.8, utilizing both time-domain and linearized frequency-domain solvers, manual meshes and adapted meshes, and various governing equations. With increased angle-of-attack, linearized and finite amplitude flutter predictions exhibit differences above 3 deg. as the flow begins to separate; the latter predictions are found to be driven by subcritical limit cycle oscillations whose strength increases with angle-of-attack. Moderate perturbation values provide a stability boundary at 5 deg. that matches the experimental data, but it is not clear how the experimental perturbation, from one test condition to the next, can be reasonably characterized.
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16:30
30 mins
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Mechanism of transonic aeroelastic instabilities via synchronization of coupled oscillators
Srikanth Vasudevan, Xuerui Wang, Roeland De Breuker
Abstract: This paper contributes towards the development of a reduced-order modelling methodology for nonlinear, unsteady aerodynamic loads for the active control of transonic aeroelastic flutter. To this end, a 1-DOF torsional NACA0012 airfoil is chosen as the test configuration. The aim is to develop the reduced-order model in nonlinear state-space form to be used in active control scenarios. Hence, a nonlinear coupled differential equation that captures the shock dynamics. The underlying hypothesis of this work is that, once these aerodynamic effects are included in the low-order model, the nonlinear trend in the flutter stability boundary, specifically in the transonic regime, will be predicted purely based on first principles, without the need for numerical or experimental corrections. In this work, we observe that the aeroelastic system could become prematurely unstable as soon as the aerodynamic flow field undergoes a Hopf bifurcation. For low amplitude airfoil pitching below a certain threshold, the aerostructural system is seen to exhibit a coupled oscillator behaviour that has an exact linear analytical formulation. The analytical formulation thus produces an accurate prediction whilst being orders of magnitude faster than the numerical simulation.
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17:00
30 mins
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Transonic aeroelastic limit cycles and their dependence on freestream conditions
Nicholas Giannelis
Abstract: In this paper, Unsteady Reynolds-Averaged Navier-Stokes (URANS) flow simulations are coupled to a single-degree-of-freedom rigid body structural solver to study the dependence of the transonic aeroelastic response of the OAT15A to variations in freestream conditions. The aeroelastic computations are validated against elastically-suspended profile wind tunnel experiments, with excellent correlation in the unsteady loads and surface pressure magnitude and phase. Mach number and angle of attack sweeps are performed for three distinct structural configurations, with the pitch eigenfrequency below, marginally above and well-above the buffet frequency. The results find a rich spectrum of nonlinear dynamic behaviour, including mode-switching, asymmetric LCOs, and Hopf and jump bifurcations. Of significance is the emergence of nontypical LCOs for the structural composition in which frequency lock-in was observed. The origins of nontypical limit cycles, which grow and then reduce in amplitude with increases in Mach number, have been debated in literature and the findings of the present study indicate a potential connection between this transonic aeroelastic phenomenon and buffet lock-in.
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17:30
30 mins
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High-Fidelity Multidisciplinary Maneuver Simulations of the Falcon 2000LX ISTAR
Martin Bauer, Johan Feldwisch
Abstract: This paper presents high-fidelity multidisciplinary maneuver simulations of the DLR research aircraft Dassault Falcon 2000LX ISTAR. These simulations are computed using the multidisciplinary process chains FSAerOpt and UltraFLoads for the DLR research project HighFly (High-Speed Inflight Validation). The goal of this project is the validation of simulation models for virtual flight testing with data measured on the ISTAR aircraft. The paper describes the individual ISTAR models and analyses: CAD geometry, CFD (DLR TAU-Code), control surface deflection modeling, CSM (MLS Nastran), aircraft mass distribution, and engine. The paper gives also a short overview of some UltraFLoads simulation processes such as CFD-CSM coupling, trim analysis, and dynamic maneuver simulation. The results of steady-state trimmed CFD-CSM coupled simulations and unsteady open-loop free-flying elastic maneuver simulations (pull-up, push-down, bank-to-bank) in clean configuration are presented. The first comparisons of the numerical simulations with the experimental data are also shown.
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