Numerical investigations on the dynamic behavior of a 2-DOF airfoil in the transitional Re number regime based on fully coupled simulations relying on an eddy-resolving technique

The paper is the numerical counterpart of the experimental investigation on the fluid–structure interaction (FSI) of a wing with two degrees of freedom (DOF), i.e., pitch and heave. Wood et al. (2020) has provided the experimental basis by studying the flutter stability of an elastically mounted straight wing (NACA 0012 airfoil) in a wind tunnel considering the transitional Reynolds number regime. Three different configurations with varying distances between the fixed elastic axis and the variable center of gravity were considered. Additional free-oscillation tests in still air were carried out in order to make the mechanical properties of the setup available for the simulations. The present contribution describes the numerical methodology applied consisting of a partitioned coupled solver combining eddy-resolving large-eddy simulations on the fluid side with a solver for the governing equations of the translation and rotation of the rigid wing. In order to prove the parameters provided by the experiment and to determine the pure material damping coefficients not available from the measurements, simulations of 1-DOF free-oscillation tests in still air are carried out and analyzed. For validation purposes the corresponding 2-DOF free-oscillation tests in still air are assessed and a good agreement with the experimental data is achieved. Finally, the wing exposed to a constant free-stream of varying strength is analyzed leading to the characterization of complex instantaneous FSI phenomena such as limit-cycle oscillations and flutter. Under full utilization of the supplementary measurements the predictions are evaluated in detail. Contrary to the experiments the simulations provide the entire fluid data and unique data for the translatory and rotatory movement allowing to investigate the causes of the observed phenomena. Both limit-cycle oscillations and flutter can be reproduced by the coupled FSI predictions.