CFD modeling of wind flow in a real urban site under low wind conditions

Examining the dispersion of hazardous agents within complex environments, whether situated in urban or remote areas globally, requires a comprehensive analysis of evolving wind patterns and atmospheric stability in hazardous zones on an hourly basis. This investigation is essential to ensure that models employed for risk assessment can furnish a timely and effective response. However, modeling complex scenarios, especially those involving low wind conditions (wind speed < 1-2 m/s) and meandering, poses challenges due to the intricate dynamics of these phenomena.This study aims to conduct numerical modeling of wind flow in an urban area, characterized by sequences of weak winds and meandering. The computational analysis utilizes the atmospheric module of the Code_Saturne Computational Fluid Dynamics (CFD) software developed by EDF R&D. The inquiry originates from a measurement campaign conducted by LMEE (Laboratoire de Mécanique et d'Énergétique d'Évry) in Evry, south of Paris, France, spanning 16 months from September 2008 to December 2009. Statistical analysis of raw measurements from the campaign reveals that almost 45% of the winds are weak, with nearly 50% falling under very stable atmospheric conditions.The CFD model is evaluated against averaged observations obtained from micro-scale measurements using an ultrasonic anemometer. The study encompasses a 1x1 km grid covering the urban area. Subsequently, meso-scale hourly measurements from nearby Météo-France stations, providing essential outputs for the CFD model, are incorporated.