# Correction of Field-Measured Wind Speed Affected by Deterministic Interference Factors
## 3 Wind Speed Revise
### PAFC Site  
The wind measured site in the hollow-layer atop PAFC is greatly important to explain the high-altitude wind field in urban areas. However, the measured wind speeds are relatively inaccurate due to the blockage of the structural pillars at the corners and numerous installed equipment. WTTs were carried out with a segmental scale model of PAFC to explore the influence of relevant factors and to study the wind speed revise when considering the influence of architectural shape and surrounding environment. The WTT was carried out in the Wind Tunnel Laboratory of South China University of Technology under the wind field of terrain category C. The segmental model of PAFC had an interception range from the tower top to 100 m below it, with a scale ratio of 1:100. The equipment was reduced to smaller scale and made by 3D printing. The maximum blockage ratio of the PAFC model in the tunnel was 3.52% and less than 5%, which satisfied the test requirement. Two Cobra probes were fixed in the wind tunnel at these positions to reflect the relationship between the wind speed of the anemometer at the site and the upstream reference point with the same height, as shown in Figure 7. The upstream reference point was located at the edge of the turntable. When the model was installed, the anemometer atop the downstream tower should be located at the center of the turntable as far as possible. Meanwhile, the upstream Cobra probe was fixed on an automatically controlled abutment and was always maintained at the anemometer point by computer controlling. Figure 7: Overview of WTT. During the test, the different wind incident directions were simulated by rotating the wind tunnel turntable, and the wind speeds of the probes were measured every 10\({}^{\circ}\) from 0\({}^{\circ}\) to 180\({}^{\circ}\) (restricted by test conditions and large structural pillars, 130\({}^{\circ}\) and 140\({}^{\circ}\) wind directions cannot be completed). Case 1 with instrument absence and case 2 with instrument presence were conducted to investigate the influence of instruments in the hollow-layer, as shown in Figure 8.  
Figure 9 illustrates the variations of wind speed of the two probes with wind directions in two cases. The wind speed of the downstream probe was significantly decreased under the wind direction of 45\({}^{\circ}\) and nearby while increased in other directions in case 1, indicating that an acceleration effect similar to pipe ventilation is found in the hollow-layer without instruments. In case 2, the wind speeds of the downstream probe were less than those of the upstream probe in different degrees except for a few wind directions, owing to the shielding effect of the instruments. Wind speeds at the measured point of the scaled model were significantly smaller than those of the reference point in approximately 100\({}^{\circ}\) directions. Figure 8: Details of the hollow-layer plane: (**a**) case 1 with instrument absence; (**b**) case 2 with instrument presence. Figure 9: Variations of the wind speed with wind direction at the measured point of the segmental model of PAFC: (**a**) wind regime of case 1; (**b**) wind regime of case 2. The variation of \(C_{\text{VI}}\) with wind direction in case 1 and case 2 is shown in Figure 10. The figure shows that, regardless of whether or not instruments exist, the \(C_{\text{VI}}\) is relatively close and changes symmetrically with 45\({}^{\circ}\) as the center, due to the geometric symmetry of the architectural scheme and the arrangement of instruments, within the wind direction range of 45\({}^{\circ}\)\(\pm\) 25\({}^{\circ}\). According to the \(C_{\text{VI}}\) at these directions, the wind speed reduction of the corresponding wind incident direction is as high as 20% due to the corner giant pillars designed for architectural requirements. In addition, the instruments greatly affected the wind speed, especially under the wind direction of 90\({}^{\circ}\) or nearby; a serious shielding effect of instruments was observed.