CFD simulation of cross-ventilation flow for different isolated building configurations: Validation with wind tunnel measurements and analysis of physical and numerical diffusion effects

摘要

Computational Fluid Dynamics (CFD) has become one of the most important tools for the assessment of natural cross-ventilation of buildings. To ensure the accuracy and reliability of CFD simulations, solution verification and validation studies are needed, as well as detailed sensitivity studies to analyse the impact of computational parameters on the results. In a previous study by the present authors, the impact of a wide range of computational parameters on the cross-ventilation flow in a generic isolated single-zone building was investigated. This paper presents the follow-up study that focuses in more detail on validation with wind tunnel measurements and on the effects of physical and numerical diffusion on the cross-ventilation flow. The CFD simulations are performed with the 3D steady Reynolds-Averaged Navier-Stokes (RANS) approach with the SST k-w model to provide closure. Validation of the coupled outdoor wind flow and indoor airflow simulations is performed based on Particle Image Velocimetry (PIV) measurements for four different building configurations. The analysis of numerical diffusion effects is performed in two parts. First, the effect of physical diffusion is analysed by changing the inlet profiles of turbulent kinetic energy within a realistic range. Second, the effect of numerical diffusion is investigated by changing the grid resolution and by applying both first-order and second-order discretisation schemes. The results of the validation study show a good to very good agreement for three of the four configurations, while a somewhat less good agreement is obtained for the fourth configuration. The results of the diffusion study show that the effects of physical and numerical diffusion are very similar. Along the centreline between the openings, these effects are most pronounced inside the building, and less pronounced outside the building. The velocity-vector fields however show that increased physical and numerical diffusion decreases the size of the upstream standing vortex and increases the spread of the jet entering the buildings. It is concluded that diffusion is an important transport mechanism in cross-ventilation of buildings, and that special care is needed to select the right amount ofphysical diffusion and to reduce the numerical diffusion, by using high-resolution grids and by using at leastsecond-order accurate discretisation schemes.