On the effects of the spanwise length on the flow past an airfoil in stall at moderate Reynolds numbers

This study investigates the influence of the spanwise periodic domain length Lz on the accuracy of numerical simulations of flow past an SD7003 airfoil (Selig–Donovan series) in post-stall conditions at an angle of attack α=14° and Reynolds number Rec=60 000. Large eddy simulations and direct numerical simulations are performed for spanwise extents ranging from Lz/c=0.2 to 2.0 to evaluate their impact on flow dynamics, aerodynamic forces, and wake characteristics. The results demonstrate a strong sensitivity of key flow features and aerodynamic coefficients to the chosen spanwise length. Domains that are too short artificially constrain three-dimensional flow structures, leading to significant overprediction of drag, lift, and unsteady lift fluctuations. This behavior is attributed to trailing-edge flow structures being forced into an unrealistically coherent spanwise configuration, which inhibits their natural three-dimensional breakdown in the wake. Analyses based on two-point correlations and flow statistics indicate that a minimum spanwise length of Lz/c≥0.8 is necessary to capture the largest turbulent scales, reduce the influence of periodic boundary conditions, and obtain accurate predictions of unsteady aerodynamic forces. The findings further suggest that previous high-fidelity studies, which used Lz/c=0.2 for computational efficiency, were insufficient to represent the full three-dimensional complexity of post-stall flow.