Wind-driven external aerodynamics around buildings and buoyancy-driven fluid motion and heat transfer in internal flow passages

Abstract

Two areas of focus are considered with respect to the resilience of buildings to withstand environmental forces and to the enhancement of building energy efficiency. First, wind-driven pressure and velocity fields surrounding a model building are calculated by means of computational fluid dynamics (CFD) in two- and three- dimensions using the Shear Stress Transport (SST) turbulence model. The sensitivity of pressure coefficient distributions over each building surface to the placement of the solution domain and to the applied boundary conditions is determined. Pressure coefficient magnitudes were found to be particularly sensitive to the distance separating the upstream boundary of the solution domain, where the atmospheric boundary layer velocity profile is specified, from the location of the building. The magnitude of pressure coefficients at each building surface tended to decrease with increasing upstream distance of the applied velocity profile. At the building roof, the three-dimensional representation of the building resolved off-roof-centerline periodic transient pressure coefficient variations whereas the two-dimensional model predicted steady-state pressure coefficients over the entire rooftop. Building energy efficiency was studied via CFD to determine buoyancy-based heat transfer and velocity distributions in an asymmetrically heated vertical-wall channel representing a double-walled building with and without obstructions placed within the vertical channel. Specifically, catwalks consisting of an array of rectangular slats were deployed at two floor levels of a three-story building. The numerical model employed is validated by comparison with experimental data from a literature source. Channel Nusselt numbers and Reynolds numbers were found to increase with the openness of the catwalk elements to flow passage and also with the channel Rayleigh number. A porous-medium model employing the Darcy-Forchheimer equation is considered as a means to represent the pressure drop of each catwalk grating. This approach yielded results of only moderate accuracy for the velocity field because the porous-medium model does not faithfully reproduce turbulence. On the other hand, an approximation-free model was successfully employed to yield highly accurate fluid flow and heat transfer results for the channel flow.