CFD simulation of the wind flow under lift-up buildings using a porous approach

Abstract

Modeling the urban climate using computational fluid dynamics (CFD) is essential for assessing urban thermal comfort and developing heat wave mitigation solutions. One mitigation strategy may rely on the enhancement of urban ventilation and the use of porous urban environments, as the lift-up, or on pilotis, buildings. Lift-up buildings have their ground floor in whole or in part supported by columns and shear walls, allowing wind flow through the building at pedestrian level. CFD modeling of these intricate geometries is computationally challenging for large urban neighborhoods. Simplifications, such as removing columns to obtain an acceptable computational cost, lead to erroneous results in the global flow pattern. To balance accuracy and computational cost, the impact of complex ground floor geometry on wind flow is modeled using a porosity sink term in the Navier-Stokes equations based on the Darcy-Forchheimer law. The improved CFD modeling of a simple lift-up building is validated with wind tunnel measurements. Simulations of wind flow around a realistic lift-up building for different wind directions determine the Forchheimer coefficients required for the porosity approach. Comparison of reference and numerical porosity results demonstrates a very good agreement in mean velocity patterns. The study demonstrates that oversimplifications, such as removing all columns, leads to an unacceptable overestimation of the wind velocity at pedestrian level. The paper highlights the benefits of the numerical porosity approach and its necessity for accurate urban-scale simulations.