Sylvie Dequand, Guy-Daniel Mortchéléwicz, Anne-Sophie Sens

DOI Number: N/A

Conference numer: IFASD-2017-054

This contribution deals with Limit Cycle Oscillations (LCO), which are sustained periodic oscillations due to nonlinearities. The study has been carried out in close collaboration between DLR and ONERA, in the framework of the High Fidelity Aeroelastic Simulation (HIFAS) project. The investigations are related to the prediction of 3D LCO on the flexible “Aerostabil” backward-swept wing. For this 3D configuration, the DLR has experimentally simulated LCO in the TWG wind tunnel in Göttingen and has also numerically predicted it using CFD-CSM coupled simulations. We present the results obtained with the elsA code developed at ONERA for these experimental cases. The study of the nonlinear behavior of the first harmonic of the generalized aeroelastic forces (GAF) as a function of the amplitude shows the existence of a mode for which the aeroelastic force goes from stable to unstable. Through dynamic fluid-structure coupling computations on this mode, with the fluid modeled by averaged Navier Stokes equations and the Menter komega turbulence model, we find the existence of limit cycle oscillations. A nonlinear reduced model of the aeroelastic force is then presented. This model is constructed from the results obtained for the first harmonic of the aeroelastic forces computed by forced excitation simulating different frequencies and different excitation amplitudes. Comparisons between the fluid calculations and the dynamic coupling simulation using the nonlinear reduced model aeroelastic forces are presented. The occurrence of LCO is also investigated for the NLR 7301 two-dimensional airfoil. As for the 3D Aerostabil wing, a nonlinear reduced model for the first harmonic of the GAF is built. The fluid-structure simulations performed with this model confirms the existence of LCO and the capability of predicting the LCO phenomenon with a single DOF system.

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In Categories: 1.Events, Computational Aeroelasticity, IFASD 2017
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