A POD-DMD augmented procedure to isolating dominant flow field features in a street canyon

Abstract

This work develops a data analysis procedure, namely Proper Orthogonal Decomposition (POD)-Dynamic Mode Decomposition (DMD) augmented analysis, to isolate the energy- and evolution-wise dominant features of flow field in a street canyon. This combination aims to extract modes imposing critical influence on pollutant dispersion from both energetic and dynamic perspectives. The two techniques were first conducted based on large-eddy simulation (LES) results. Subsequently, based on the POD and DMD ranking, the extracted modes were classified into three types: (1) type 1: energetically & dynamically significant mode; (2) type 2: energetically significant & dynamically insignificant mode; (3) type 3: energetically insignificant & dynamically significant mode. Results show that mode type 1 contribute to the mainstream flow and the main vortex structures, which can be observed near the stagnation point, the separating point, and the fluid reattachment area. Mode type 2 throws light on where the turbulent kinetic energy is the largest, leading to periodically sudden pollutants increase on the building roof and the wake region. Mode type 3 contributes to the long-term reversed flow structures occurring near the stagnation point, inside the street canyon, and in the wake region. This technique can provide a systematic analysis of the flow field within a street canyon, and it also provides help for potential applications at a city scale, such as solving pollutant dispersion issues in urban areas.

Numerical study on aerodynamic characteristics and flow field of a circular cylinder equipped with a C-ring behind at Re = 1000

“…To better understand the mechanism behind the effect of the C-ring on the cylinder, the time mean spanwise velocity behind the cylinder and C-ring was obtained, and the instantaneous vortex structures were extracted to comprehensively investigate the interference effect of the C-ring (Fu et al, 2023).…”

“…To better understand the mechanism behind the effect of the C-ring on the cylinder, the time mean spanwise velocity behind the cylinder and C-ring was obtained, and the instantaneous vortex structures were extracted to comprehensively investigate the interference effect of the C-ring (Fu et al, 2023). Corresponding to the time mean base pressure coefficients, the time mean spanwise velocity behind the cylinder at a distance of 0.1D (x/D = 0.6) was extracted as shown in Figure 14.…”