Experimental study of the turbulent characteristics in the wake of tall building clusters

This manuscript mainly explores the characteristics of turbulence quantities in the wake of tall building clusters of different array size ( 𝑁 ) and building spacing ( 𝑊_𝑆 ) arranged in an aligned and regular grid in the flow direction. Velocity fields are measured in a wind tunnel using three-dimensional laser Doppler anemometry. Results show a delayed recovery of 𝑢_𝑟𝑚𝑠 and 𝑣_𝑟𝑚𝑠 (defined as the root-mean-square of the streamwise and lateral velocities, respectively) in the wake flow compared with the mean flow. Based on the turbulent fluctuations, the extents of the near-, transition- and far-wake regions in Mishra et al. (Boundary-Layer Meteorol., vol. 189, 2023, pp. 1–25) are revisited. In the near wake, we observe a significant reduction in 𝑢_𝑟𝑚𝑠 and 𝑣_𝑟𝑚𝑠 in the wake of a 4×4 cluster compared with that of a single building. In the transition region, the turbulence intensity magnitudes within the cluster reduce to below their free-stream counterpart; this reduction is associated with the slowly varying nature of the normalised wake deficit in the streamwise direction. The recovery of the root mean square in the far-wake region is observed for  𝑥≥2.5𝑊_𝐴 (where  𝑊_𝐴 is the width of the cluster), with the mutual interaction of the wakes formed behind the individual buildings reducing with an increase in  𝑊_𝑆, resulting in a faster recovery of the turbulent fluctuations. Finally, wavelet analysis suggests the existence of multi-scale vortex-shedding frequencies downwind of tall building clusters.