The target of this paper is the negative peak wind forces in the direction toward the outside of the building for designing the cladding/components of rooftop signboards. Focus is on the edges of signboards where the largest wind forces are induced. A systematic wind tunnel test was conducted, changing the building shape and the shape and installation location of signboard. The most critical negative peak wind force coefficient irrespective of wind direction occurred in a wind nearly parallel to the signboard. It was fond that a non-dimensional parameter defined by , where l is the distance between the building's windward edge and the signboard's windward edge, and H and B' are the height and width of the building's windward wall, respectively, was an important factor for . When = 0.7, the value of was at its minimum, the largest in magnitude. A flow visualization indicated that a separated flow reattached on the building wall near = 0.6. The separated flow fluctuates with the inflow's fluctuation. Consequently, the local flow near the top of the building instantaneously turns toward the outside of the building, which may cause near the edge of signboard.

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The effects of an urban geometry on turbulent airflow at a pedestrian level have been investigated through wind-tunnel experiments and numerical simulations. However, previous studies faced limitations in storing sufficient datasets for understanding the dominant coherent motion. This study investigates the effect of the spatial resolutions of the datasets on extracted dominant modes of the pedestrian-level wind within a simplified canopy determined by large-eddy simulations. Singular value decomposition analysis was performed on both the original and down-sampled datasets. The results revealed similar singular modes across the different sampling resolutions. Additionally, low-rank approximation analysis was performed on the wind speed fields at pedestrian level to understand the influence of dominant modes on the gusty winds. The results suggested that not only low-rank but also high-rank modes are important in determining gusty phenomena, implying that the interrelationships between modes are necessary.

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