*Mode Interpretation of Aerodynamic Characteristics of Tall Buildings Subject to Twisted… DOI: http://dx.doi.org/10.5772/intechopen.103757*

turbulence intensity profile but different twisted angle profiles. Thus, only one set of data is provided in **Figure 5(a)**. Evidently, both the numerically and experimentally replicated wind profiles agree well with the targeted result. The simulated twisted wind conditions, TWP15 and TWP30, had the largest twisted angle at the ground level, which is about 15°and 30°, and both of them well conformed to the targeted variation trend in the vertical direction as expressed in Eqs. (7) and (8). The longitudinal wind velocity spectrum at the reference height is in good agreement with the von Karman spectrum within a relatively wide scope, including the inertial subrange, as shown in **Figure 5(c)**.

The distribution of the pressure coefficients along the circumference of the building at a height of z = 2/3H obtained by LES and wind tunnel test are compared in **Figure 6** for cases CWP and TWP30. Affected by twisted flow, the location of the largest positive pressure and stagnation point is moved towards the right-side of the building on the windward side. When exposed to CWP, the pressure distributions on the left- and right- side surfaces of the building are symmetrical, while under TWP, significant differences are noted both for mean and fluctuating coefficients. The most distinctive discrepancy of the mean pressure between CWP and TWP30 occurs at the right-side surface of the building, simply because it becomes partially windward when the building is exposed to the twisted wind. A similar phenomenon can also be observed for the fluctuating pressure with the largest difference 86.84% appearing at monitoring point 22. Notably, wind twisting can significantly magnify the mean *Cp* while greatly weakening the fluctuating *Cp* on the right-side surfaces.

Generally, the pressure distribution obtained in LES at 2/3 height of building shows reasonably good agreement with its counterpart in wind tunnel testing, especially for mean Cp. As a result, although small discrepancies exist, the numerical methods used in this study can still provide reliable and reasonable results for the evaluation of the twisted-wind effect.

#### **Figure 6.** *Mean and fluctuating pressure coefficients at height of z = 2/3H obtained by LES and experiment under CWP and TWP30.*
