Aspect ratio effects on spatiotemporal correlations and coherent structures of buildings specifically for twisted wind

In this study, flow fields of square cross-section buildings with three aspect ratios (AR=breadth/height=1:1, 1:4 and 1:6) under conventional wind profile (CWP) and twisted wind profile (TWP) are simulated by Large-eddy simulation. The Reynolds number is 22,000 based on breadth. The correlation of in-plane and out-of-plane velocities is defined to investigate the spatial-temporal correlation of wake flows of buildings specifically for twisted wind. Proper orthogonal decomposition (POD) is utilized to capture coherent structures and their mode correlations. Results show that twisted wind noticeably changes time-averaged flow structure and wake dynamics both qualitatively and quantitatively. The effect of aspect ratio on flow field specifically for TWP becomes more protruding and is categorized into two types of patterns. For the low-rise building pattern, TWP is more resembling condition of CWP with a certain wind incident angle, due to the advent of conical vortex and shift mode, and the correlation of wake field feature is magnified at all heights of buildings. For the tall buildings pattern, under TWP, the predominant coherent structure at frequency of 0.1 is weakened, and correlation of wake feature related to Karman vortex is suppressed. The out-of-plane correlation of velocity verifies the wake structure distortion and stronger momentum exchange due to the dominated upwash vortex under TWP.