Buoyant flows in street canyons: Validation of CFD simulations with wind tunnel measurements

Abstract

Computational fluid dynamics (CFD) is often used to predict flow structures in urban areas for the determination of pollutant dispersion, human comfort or heat fluxes. During daytime building façades and ground surfaces are heated by solar radiation and thereby induce buoyancy, which changes the flow field around buildings significantly. The CFD models used to simulate buoyant flow fields in urban areas are not sufficiently validated. This study aims to validate CFD simulations for buoyant flows in urban street canyons by comparison with wind tunnel measurements. 2D steady RANS (Reynolds-Averaged Navier-Stokes) CFD simulations were conducted with different near-wall treatments. Velocity, turbulent kinetic energy and temperature profiles from CFD were compared with the measured flow fields (measurement technique: particle image velocimetry). Isothermal cases as well as cases with leeward wall or windward wall heating or all surfaces heated were considered. The results show that CFD can predict the general flow structures and the influence of buoyancy. The detailed flow field inside the street canyon is strongly dependent on the flow structure within the shear layer at the top of the street canyon. Therefore to get accurate results for the flow profiles inside the street canyon, the flow within the shear layer has to be predicted correctly.

The role of materials selection in the urban heat island effect in dry mid-latitude climates

“…Allegrini et al [2] have conducted the validation of FLUENT using 2-D steady RANS simulations for the case of a heated street-canyon under a background wind as characterized by different Froud and Reynolds numbers. For the validation mean velocity and turbulent kinetic energy were assessed.…”

CFD Analysis of Urban Canopy Flows Employing the V2F Model: Impact of Different Aspect Ratios and Relative Heights

“…e choice of a 2D model allows lower computational costs without compromising the accuracy of the results [14][15][16][17][18]. In order to test the e ectiveness of this choice, both the 3D and 2D models have been run and compared with the experimental data.…”

“…ey observed that short-time variations of wind velocity can greatly influence the mass transfer rate between the canyon and the overlying boundary layer. Allegrini et al [17] carried out 2D steady RANS simulations with different near-wall treatments in order to validate numerical results for buoyant flows in urban street canyons by comparison with wind-tunnel measurements. ey compared the results of different turbulence models (STD k-ε, realizable k-ε, k-ω, Spalart-Allmaras, and Reynolds stress model (RSM)), showing a better agreement of the STD k-ε model with the NEWFs (nonequilibrium wall functions) than the LRNM (low-Reynolds number modeling).…”

A numerical study of diurnally varying surface temperature on flow patterns and pollutant dispersion in street canyons

“…Its flow regimes are mainly determined by canyon geometry, ambient wind condition, atmospheric instabilities, and building layout (Vardoulakis et al, 2003;Georgakis and Santamouris, 2004). Many field measurements, laboratory experiments and numerical simulations have been conducted based on different meteorological and geometrical factors (Li et al, 2006;Allegrini et al, 2014). Richards et al (2006) conducted a stratified wind tunnel experiment to analyze the thermal effects of leeward wall heating; he concluded that cavity eddies tend to be strong with ground heating.…”