Improving aerodynamic damping prediction in a vibrating 4:1 rectangular cylinder via detached eddy simulation of spanwise correlation

Predicting the onset of aeroelastic instabilities in crossflow structures requires accurate estimation of aerodynamic damping. Conventional strip-theory flow models are attractive for their low requirements, but neglect spanwise decorrelation and its dependence on vibration dynamics, leading to conservative predictions of aerodynamic damping. This study evaluates detached eddy simulation (DES) as a higher-fidelity alternative, leveraging its resolved turbulence scales to capture natural spanwise correlations under vibration. A dedicated DES study was conducted for a 4:1 rectangular cylinder undergoing forced heave and pitch oscillations. Predicted in-phase (aerodynamic stiffness) and out-of-phase (aerodynamic damping) motion-induced loads were benchmarked against wind tunnel data and two-dimensional unsteady Reynolds-averaged Navier–Stokes (2D-URANS) results. DES markedly improved aerodynamic damping predictions for both motion types, while stiffness estimates showed only modest gains. Quantitatively, the DES-predicted aerodynamic damping curves exhibit low horizontal offset (±7%) and near-unity shape and scale correspondence to experiments. Damping extrema were predicted with errors between 9% and 20%—outperforming 2D-URANS errors by over an order of magnitude; analysis of spanwise correlation contours and flow patterns clarified these trends. Notably, both methods reproduced phase angles and critical reduced velocities with similar accuracy. For design practice, DES offers significant advantages in mass-damping specification. In contrast, two-dimensional models remain valuable for efficient design-space exploration, providing similarly-accurate stability envelope estimates at minimal cost. These findings support a staged design workflow in which scale-resolving simulations are suitable for late-stage specification, and highlight priorities for future validation, namely, quantifying uncertainty in domain span and spanwise resolution in the forced vibration framework.