Influence of sand fence opening shapes on aeolian sand transport and deposition under fixed porosity

Perforated sand fences are widely used to mitigate aeolian sand hazards along desert railways; however, generalized links between sand fence opening shapes and downwind deposition remain limited under fixed porosity. In this study, wind tunnel measurements combined with validated numerical simulations quantify how opening shapes, including opening scale, perimeter complexity, slit aspect ratio, and slit orientation, regulate wake recovery, near-surface shear, and sand flux redistribution at a fixed total porosity. Across all geometries, a near-fence acceleration zone is followed by momentum loss and downstream recovery, while the recovery length varies systematically with aperture design and governs the extent and persistence of the low-shear shadow that controls sand trapping. Straight slits generate spatially coherent low-velocity wakes, expand low-shear areas, and suppress re-entrainment, promoting a continuous deposition belt immediately leeward of the fence. In contrast, inclined slits redirect momentum upward or laterally, shortening recovery while forming directional shear corridors that shift and elongate deposition zones and may enhance lateral export. The centerline particle volume fraction peaks at the fence and decays within one to two fence heights, with the longest downstream tails associated with geometries that promote lifted jet transport. These results provide geometry based predictors and design guidance for selecting opening shapes to stabilize near-leeward trapping belts or steer deposition away from sensitive infrastructure in arid transport corridors, under the present fixed-porosity conditions.