On the generation and destruction mechanisms of arch vortices in urban fluid flows

TL;DR

This study uses advanced decomposition techniques to analyze the formation and destruction of arch vortices in simplified urban flow models, revealing their impact on pollutant dispersion and urban sustainability.

Contribution

It introduces a novel application of higher order dynamic mode decomposition to identify vortex mechanisms in urban flows, enhancing understanding of pollutant dispersion.

Findings

Arch vortices significantly influence pollutant dispersion in urban areas.

Vortex-generating and vortex-breaking modes are identified and characterized.

Arch vortex formation increases pollutant concentration, affecting urban sustainability.

Abstract

Studying and interpreting the different flow patterns present in urban areas is becoming essential since they help develop new approaches to fight climate change through an improved understanding of the dynamics of the pollutants in urban environments. This study uses higher order dynamic mode decomposition (HODMD) to analyze a high-fidelity database of the turbulent flow in various simplified urban environments. The geometry simulated consists of two buildings separated by a certain distance. Three different cases have been studied, corresponding to the three different regimes identified in the bibliography. We recognize the characteristics of the well-known arch vortex forming on the leeward side of the first building and document possible generation and destruction mechanisms of this vortex based on the resulting temporal modes. These so-called vortex-generating and vortex-breaking modes are further analyzed via proper-orthogonal decomposition. We show that the arch vortex plays a prominent role in the dispersion of pollutants in urban environments, where its generation leads to an increase in their concentration; therefore, the reported mechanisms are of extreme importance in the context of urban sustainability.