## 3 Results
### Flat-roof Building
#### 3.1.4 Flow Pattern Comparison with Other Flat-Rood Buildings  
In order to compare the flow above high-rise buildings with available results for low-rise buildings, a comparison with the databases AIJ and CEDVAL is proposed. The CEDVAL database reports flow measurements around a cube (\(H\)/\(D\) = 1:1) obtained through laser Doppler anemometry (LDA two-component system) for various wind directions. At 0\({}^{\circ}\), a large separation over the top of the roof is detected. However, the actual size of the separation length is not available due to the lack of measurement data near the roof, as the closest measurement positions are located at z/\(D\) = 0.2. The maximum velocity increase of 21% occurs above the central point of the cube at z/\(D\) = 0.6. This is followed by slightly higher turbulence intensity levels than the reference ones [39]. The CEDVAL database also considers an incident angle of 45\({}^{\circ}\). Close to the roof, i.e., at a height of z/\(D\) = 0.2, the normalised velocity increase is in the range 12-15%. The maximum value is reached at a similar location as in the present study, i.e., close to the downstream point 54. As also found in the present study, at 45\({}^{\circ}\), turbulence intensities \(I_{\textit{U}}\) and \(I_{\textit{W}}\) are comparable to or even lower than the reference inflow values. A significantly smaller separation bubble, as compared to the current case, is instead reported in the AIJ dataset [37], which considers a square isolated flat-roof building, at 0\({}^{\circ}\), with a ratio of \(H\)/\(D\) = 2:1. Based on the reversed flow detected, the reattachment length can be estimated at \(\sim\)1/4\(D\), which is lower than in the present case. This can be attributed to the higher turbulence intensity in the inflow. In addition, a slightly lower flow acceleration \(\sim\)24% is found above the location at 1/4\(D\) at height z/\(D\) = 0.375, compared to the current high-rise case, where similar turbulence intensities to the reference one are recorded. Comparing the surface pressure patterns on the flat roof from the low-rise buildings [37; 39] and the current high-rise building, it can be concluded that the surface pressure contours are consistent for a given wind direction. These patterns reveal the existence of analogous flow structures, i.e., separation bubble at \(\alpha\) = 0\({}^{\circ}\) and conical vortices for the oblique wind direction, as observed in Figure 6. The Architectural Institute of Japan published two databases on pressure measurement on low-rise and high-rise buildings. Those experimental campaigns were mainly focused on the sides of the buildings and only measurements on the low-rise buildings included measurement positions at the flat roof. Figure 9 compares the mean pressure coefficient over the centre line of two cubes havingrespectively \(H\)/\(D\) = 1:2 and \(H\)/\(D\) = 1:1, taken from the AIJ database, for the two wind directions 0\({}^{\circ}\) and 45\({}^{\circ}\). As mentioned above, the size of the hump shape of the pressure coefficient curve, which is related to the high negative pressure in the separation region, can be used as an estimate of the size of the separation bubble. Figure 9 shows a possible trend for the hump shape, which is increasing alongside the height of the building. A smaller increase in size seems to occur for 45\({}^{\circ}\), yet more windward measurement points would be required for a more detailed analysis. The increase in the size of the separation bubble is combined with an increase in the acceleration effect above the roof. The velocity measurements over buildings with different aspect ratios, namely \(H\)/\(D\) = 1:1 from the CEDVAL database; \(H\)/\(D\) = 2:1 from the AIJ database; and \(H\)/\(D\) = 3:1 from the current study, reveal that the wind acceleration increases together with the building height. Further, the CFD study by [PERSON] et al. [34] shows the same conclusion regarding the acceleration effect over the barrel-vainted roof of a high-rise building with three different heights.