# A Parametric Study of Wind Pressure Distribution on Facades Using Computational Fluid Dynamics
## 5 Discussion and Interpretation  
### Sheltered Case  
To establish the efficiency of the facade configurations, the effect of the geometry on wind loading was determined. Loading was based on peak net pressures, which represent a conservative estimate of actions on structures. This applies both to the context of structural analysis and the CFD modeling approach here, as improved mesh density converges toward smaller values for peak forces and moments (Table 4). Figure 15 presents peak net pressures for wind acting normal to the critical fin, in each case. Fin length was normalized with net pressure as a percentage from the fin's upper end. The least efficient design is for the fin attached directly to the building, with relatively high pressures between the fin's ends. Comparing the use of an 80 mm and a 160 mm bracket length (or gap distance), net pressures were reduced by increasing the space between the building and the fin. Net pressures related to the longest fin with the widest gap at the building has a similar shape compared to the 560 mm long fin with a bracket 160 mm in length, except at the end nearest to the building. This highlights the differences that result from extending the opening on the flow, with relative differences in the Venturi Effect. The phenomenon tends to reduce the magnitude of pressures at the end of the fin, nearest to the building. It is interesting to note the linear variation of pressure near the two ends of the plots. The variation of net pressure was defined in terms of set data points. Data outside these positions was excluded from measurement with the application of linear approximation used to establish values between known data points. The fin ends--where sharp corners are apparent--represent extremes for the analysis, as results indicate a relatively small loading in terms of windward pressure while also tending to have large leeward suction acting at the point furthest from the building structure. Therefore, the profile of net pressure near the ends of the critical fin can appear unlike the remainder of the fin's length, with the interpolated section no greater than 5 cm long contributing a negligible loss of accuracy. Figure 15: Peak net pressures for models ‘1’, ‘5’, ‘11’ and ‘13’ versus distance from the top of the fin as a percentage of total fin length. The results of the models form the basis of interpolating values for forces and moments that act throughout the population of facade configurations. Figure 16 defines peak wind loading as force across a normalized 1-m length of fin over a per meter vertical height (in units of kN/m). Wind acts normal to the critical fin in each case. In all cases, the critical fin is established as the leading fin. The significance of this load, from a design perspective, is that it imparts the maximum stress to the fin, facilitating the process of selecting the fin's material based on its strength properties for the demand imposed. Therefore, the most efficient designs involve minimizing loading that leads to a more economical use of material. It is apparent that peak force decreases by lengthening the bracket, where the fin length is fixed. The more the flow is constricted with the Venturi Effect, the more intense the continuity induced suction on the leeward face of the fin. As a result, the Venturi Effect tends to increase net pressures over the length of the fin. Stresses reduce as fin length increases between 400 mm and 560 mm, where brackets are employed. Improvements in efficiency of up to 22% are apparent. The wind load is spread more evenly in these cases as the benefits of the Venturi Effect are utilized without the same relative impact on the continuity of the flow--due to better aerodynamic performance. In contrast loading increases with fin length beyond 560 mm, however efficiencies specifically occur with for the longest fins, with brackets at 320 mm and 400 mm. The practice of attaching the fins directly to the building has an optimal efficiency in cases where the length is 400 mm.