Impact of Wind Direction on Flow Over a Realistic Urban Area: A Large-Eddy Simulation Study

TL;DR

This work addresses how wind direction modulates urban canopy flows by performing high-resolution LES over a realistic Barcelona district with ~5\times10^8 degrees of freedom and ~1 m pedestrian-level resolution. A concurrent precursor inflow and a rotation-based setup enable four wind directions, revealing that double-averaged velocity and turbulence statistics are remarkably similar across directions, even though instantaneous fields differ significantly. The results identify a shear-driven mixing layer located below $H_{avg}$ and turbulence maxima near the tallest buildings, underscoring morphology-driven momentum transfer and rooftop influence on turbulence. The findings provide a high-fidelity database for validating urban canopy models and for developing surrogate predictors, with implications for pollutant dispersion, pedestrian comfort, and urban resilience under varying wind directions.

Abstract

We conducted high-resolution large-eddy simulations over a real urban district in Barcelona to examine the impact of wind direction on near-ground flow. The computational mesh resolves over 500 million degrees of freedom, with a spatial resolution on the order of 1 m at pedestrian level. This allows a detailed analysis of mean velocity and turbulence patterns within the canopy layer. Although instantaneous flow fields differ significantly between cases, double-averaged profiles of velocity and turbulence intensity remain remarkably consistent across all wind directions. The results reveal a shear-driven mixing layer below the average building height and turbulence maxima near the tallest buildings, highlighting the influence of urban morphology on the development of flow and turbulence.

Figures (4)

• Figure 1: (a) Map of Barcelona including the zone under study. (b) computational domain including the online precursor domain
• Figure 2: Comparison between the different meshes and experimental data from leitl2024. (a)Vertical profiles of the streamwise velocity at different stations. (b)Root-mean-square (rms) values of the fluctuations at different stations.
• Figure 3: Effect of wind direction on pedestrian-level flow at 2 m height. Each column corresponds to a different wind direction ($0^\circ$, $67.5^\circ$, and $90^\circ$ from left to right). Panels (a–c) show instantaneous velocity fields, (d–f) the mean streamwise velocity, and (g–i) the turbulent kinetic energy. $U_{ref}$ is taken as the velocity at the top of the precursor domain.
• Figure 4: Vertical profiles of (a) mean streamwise velocity and (b) streamwise velocity fluctuations, non-dimensionalized by the friction velocity $u_*$ for four wind directions ($0^\circ$, $67.5^\circ$, $90^\circ$, and $180^\circ$).