Stall cells are spanwise-organized three-dimensional separation patterns that may develop near static stall and can significantly modify aerodynamic loads on wind-turbine airfoils. This work investigates near-stall aerodynamics of the DU 91-W2-250 airfoil using unsteady RANS (URANS) and Improved Delayed Detached Eddy Simulation (IDDES). A finite spanwise simulation domain is constructed by extruding the airfoil section, with periodic boundary conditions imposed at the spanwise boundaries. Motivated by the stall-cell spacing reported to be on the order of two chord lengths, the spanwise extent is set to 2c [1]. All cases share the same streamwise/normal mesh resolution and time-integration settings to enable consistent comparisons. Several spanwise grid resolutions are considered to obtain and compare solutions with and without stall cells under otherwise identical operating conditions. Stall cells are identified from cellular patterns in time-averaged limiting streamlines on the suction surface, manifested as spanwise variations in separation and reattachment footprints. Aerodynamic responses are assessed using mean lift and drag coefficients, together with the amplitudes of lift and drag oscillations. Across the near-stall conditions examined at a Reynolds number of Re=3.0×106, stall-cell solutions show reduced mean lift, increased mean drag, and smaller lift and drag oscillation amplitudes than the corresponding non-stall-cell solutions. Compared with URANS, IDDES strengthens the stall-cell-induced changes in the mean loads and predicts larger force fluctuations than URANS, but the predicted lift reduction and drag increase remain weaker than those measured in experiments. Unlike the NACA0012 results of Manni et al. [2], where a negative-slope segment of the lift curve is associated with stall-cell spacing consistent with the criterion of Gross et al. [1], the present DU25 simulations produce stall-cell solutions while the lift-curve slope remains positive. These results highlight the need to account for stall-cell formation when interpreting near-stall CFD predictions and comparisons with experiments.