**3. Data resources**

#### **3.1 Wind pressure data resources**

Pressure measurement testing was carried out on a rectangular tall building, of cross-Section 180 mm � 60 mm (Breadth�Depth) and height of H = 600 mm. The pressure distribution on the 1:400 scaled building model was measured using a DSM3400 synchronous multi-pressure sensing system (SMPSS). **Figure 1** shows arrangement details of the pressure taps and experimental setup. Pressure taps were arranged in 14 rows �12 columns on the windward/leeward surfaces and in 14 rows �4 columns on side surfaces. The sampling frequency and duration were 330 Hz and 90 s respectively. In this study, the approaching wind perpendicularly attacking the relatively wider and narrower surface of the building correspond to two different working conditions, i.e., angle of attack (AOA) of 0 degree and 90 degrees respectively.

The three targeted wind profiles have similar distributions of velocity and turbulence but different twisted angle profiles. Specifically, the wind speed and turbulence intensity profiles follow power-law functions with exponents of 0.11 and � 0.24. The maximum twisted angles are 0°, 15° and 30°, thus the profiles are respectively labeled CWP, TWP15 and TWP30. It should be noted that variation of twisted angles with height for TWP15 and TWP30 conforms with the negative power curve expressed in Eqs. (7) and (8), and as given in [22].

$$\theta\_{15}(z) = \mathbf{15} \times \exp\left(-0.0976 \times (z/25)\right) \tag{7}$$

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

$$\theta\_{\text{30}}(z) = \mathbf{30} \times \exp\left(-0.106 \times (z/25)\right) \tag{8}$$

where *θi*ð Þ*z* represents the twisted angle measured at the height z; the subscript i denotes the maximum twisted angle of TWP, herein, i = 15 and 30.

Three types of wind fields (CWP, TWP15 and TWP30), were generated in a wind tunnel by using passive simulating facilities. As shown in **Figure 2(b)** and **(c)**, to replicate the twisted wind, the wooden vane system was placed 5 m upstream away from the central axis of the building model, and the windward ends of the single wooden vane were isolated 1 m from each other. It should be noted that the wooden vane employed in this study was adjustable, indicating that the wooden strip at a certain height could be offset at any desired angle. Moreover, to compensate for the dissipation near the wind tunnel ground, three rows of roughness elements were rotated at a certain angle are set in a stagger arrangement and placed between the wooden vane

#### **Figure 2.**

*Experimental setup and details: (a) distribution of pressure taps on building model; (b) TWP test arrangement in wind tunnel; (c) section plan of the experimental setup.*

system and the building model. To determine the region with uniform twisted flow properties, a grid measurement system constituted by blue dash lines was utilized to monitor the flow features at each grid point. After trial and error, it turned out that the targeted twisted wind can maintain consistent flow properties within a rectangular region (shaded in orange) with dimensions of 1.5 m � 2.0 m (width �length) around the turntable center. *zref* indicates the reference height which is located at the building roof (z = 0.6 m); *Uref* denotes the reference velocity and equals 6.2 m/s; *Iref* represents the reference turbulence intensity and equals 6.9%. According to the reference wind speed *Uref* and building breath *<sup>B</sup>*, the Reynolds number is calculated as *Re* = 2.55 � 104 .

#### **3.2 Flow field data resources**

#### *3.2.1 Inflow turbulence generation*

Appropriately replicating the inflow turbulence features is a requisite for obtaining accurate LES simulation results. In this study, the narrowband synthesis random flow generator (NSRFG) technique is utilized to simulate inflow turbulence by generating time history series of the fluctuating velocity. Turbulence integral scales (see Eqs.(9)– (11)) conform to those in wind codes (AIJ, 2004; ESDU 85020, 2001), which are also identical to the setting given in [7]; the velocity distribution in the frequency domain corresponds to the von Karman spectrum (see Eqs. (12)–(14)), which can reflect typical spectral features of the turbulent ABL flow in a wind tunnel. The superimposition of the zero-mean fluctuating component and the mean wind profile formulate the initial inflow boundary condition. For specific implement procedures, one can refer to the work of [23]. Note that the profiles of wind speed, turbulence intensity and twisted angle are consistent with the setting in the wind tunnel.

$$L\_{\rm u}(\mathbf{z}) = \mathbf{100} \cdot \lambda\_L \cdot \left(\frac{z}{\mathbf{30}\lambda\_L}\right)^{0.5} \tag{9}$$

$$L\_v(\mathbf{z}) = \mathbf{0}.5 \frac{\left(\sigma\_v\right)^3}{\sigma\_u} L\_u(\mathbf{z}) \tag{10}$$

$$L\_w(\mathbf{z}) = \mathbf{0}.5 \left(\frac{\sigma\_w}{\sigma\_u}\right)^3 L\_u(\mathbf{z}) \tag{11}$$

$$\mathcal{S}\_{\boldsymbol{u}}(\mathbf{f}) = \frac{4(I\_{\boldsymbol{u}}\boldsymbol{U})^{2}(L\_{\boldsymbol{u}}/\boldsymbol{U})}{\left[\mathbf{1} + \text{70.8}\left(\boldsymbol{f}L\_{\boldsymbol{u}}/\boldsymbol{U}\right)^{2}\right]^{5/6}}\tag{12}$$

$$\mathcal{S}\_{\boldsymbol{v}}(\mathbf{f}) = \frac{4(I\_{\boldsymbol{v}}\boldsymbol{U})^{2}(L\_{\boldsymbol{v}}/\boldsymbol{U})\left[\mathbf{1} + \mathbf{1}\mathbf{8}\mathbf{8}.4\left(\mathbf{2}\mathbf{f}L\_{\boldsymbol{v}}/\boldsymbol{U}\right)^{2}\right]}{\left[\mathbf{1} + \mathbf{7}\mathbf{0}.\mathbf{8}\left(\mathbf{2}\mathbf{f}L\_{\boldsymbol{v}}/\boldsymbol{U}\right)^{2}\right]^{11/6}}\tag{13}$$

$$\mathbf{S}\_{w}(\mathbf{f}) = \frac{4(I\_{w}U)^{2}(L\_{w}/U)\left[1 + \mathbf{188.4}\left(2\mathfrak{f}L\_{w}/U\right)^{2}\right]}{\left[1 + \mathbf{70.8}\left(2\mathfrak{f}L\_{w}/U\right)^{2}\right]^{11/6}}\tag{14}$$

where *λ<sup>L</sup>* is the scaled ratio; *L*(*z*), *I*(*z*) and *S*(*z*) are the turbulence integral scale, turbulence intensity and power spectral respectively. The subscripts *u*, *v* and *w* denote *Mode Interpretation of Aerodynamic Characteristics of Tall Buildings Subject to Twisted… DOI: http://dx.doi.org/10.5772/intechopen.103757*

the components of the physical quantities in the along-wind, crosswind, and torsional directions respectively; *f* is the frequency.
