Porous fences can reduce dust emissions from storage piles in open storage yards, but their sheltering effect depends on the airflow structure around the pile, and the shear stress distribution on each surface. In this study, static flow fields were numerically simulated using the standard k-ε turbulence model; the shear stress characteristics and distribution on the windward side, flat-top surface, and leeward side of a typical prismatic material stack were analyzed. The distribution of the aerodynamic structure of each surface of the storage pile was determined according to the flow field data for fences of the porosities ε = 0, 0.2, 0.3, 0.4, 0.5, and 0.6. The results indicated that at low porosities (ε = 0, 0.2) a recirculating flow appeared in the region between the fence and the pile. The shear force acted downward the windward slope, and the maximum dust emission occurred at two-thirds the height of the windward side, rather than at the top, as in unfenced conditions. Using the porous fence simulated in this study, shear stress on the windward side and the flat-top surface first decreased, then increased with increasing porosity; the lowest porosity values were 0.2 and 0.3, and the shear stress on the prismatic leeside changed little with increasing porosity. The numerical predictions indicated that a fence with porosity between 0.2 and 0.3 is optimal.