A numerical simulation method is proposed for the generation of homogeneous isotropic turbulence and is applied to the investigation of the spanwise coherence aerodynamic force on a stationary airfoil. First, the inflow turbulence is generated by modeling a grid at the inlet of the computational domain. To verify the accuracy of the generated turbulence field, a series of relevant parameters are compared with the results of wind tunnel tests and previous studies. A model with NACA 0015 profile is then placed in the downstream turbulence. The relationship between the spanwise correlation width of the vertical turbulence component and the lift force is determined. Possible mechanisms for the result are discussed. This study demonstrates that the proposed turbulence generation method is an effective tool for investigating the spatial distribution of unsteady aerodynamic loads on elongated bodies.