Implementation Of Arbitrary Collocated Hexahedron Grid And Its Application In Numerical Simulation Of Wind Flow Around Buildings

Numerical modeling of wind fields around buildings has attracted wide attention and has been investigated in depth in recent years, because of its various advantages such as high computational efficiency, convenience in processing numerical results and low cost. The accuracy of the numerical results is not only related to the adopted turbulence model, but more importantly, to the employed grid system and the compatibility between the numerical method and the grid system. As the geometrical configurations of buildings become more complex and the interaction between multiple buildings attracts more attention, more and more importance is being attached to the technique of generating grids.Currently, three kinds of grid systems, i.e., the structured grid systems based on Cartesian coordinates, the grid systems and the non-structured grid systems, are widely used in modeling building wind fields. All these grid systems have their own advantages and limitations. Therefore, it is very important for the numerical modeling to make full use of the advantages of the three kinds of grid systems and consider the peculiar characteristics of the building wind fields in a view to developing a comprehensive numerical model consisting of efficient numerical methods and grid generation techniques which are general and effective for both regular and irregular geometrical configurations.This paper proposed and generated grid systems composed of arbitrary collocated hexahedrons for the first time. It is argued that most modeled domains are regular and can be regarded as integrations of multiple initial grids with hexahedrons or their best approximations. These initial grids are then discretised according to the size control parameter and numbered in the same way as for the structured grids. The general grid system composed of arbitrary collocated hexahedrons is finally generated. This grid system not only keeps the simple data structures as used in the structured grid systems, but also allows complex boundaries to be truly reflected. The grid generation and adjustment are thus very simple and effective, even for very irregular geometrical configurations of buildings.Based on the above-proposed arbitrary collocated grid systems with hexahedrons, this paper uses the finite volume method to discretise the governing equation. Corrections are explicitly made in the source term of the governing equation to consider the negative effects of mesh non-orthogonality and dislocation between adjacent elements. The pressure-corrected equation compatible with the grid systems is also given. The general SIMPLE algorithm is also established. These lead to a comprehensive numerical model for effective and efficient modeling of the wind fields around buildings, which has not been reported in the literature. An in-house computer program, named Wind Simulation of Buildings (WSB), is developed in this study based on the numerical model. This program is coded using FORTRAN and MATLAB languages. It is capable of modeling the wind fields around a single building or a group of buildings.In order to validate the developed program WSB and the proposed arbitrarycollocated hexahedron grid systems, they are first applied to model the wind field around a double-sloped building model. The numerical results are compared with those from the orthogonal grid consisting of cubes and those from the wind tunnel tests respectively. The wind field around a low-rise buildings with gabled roof designed against typhoon is also modeled using WSB and the numerical results are compared with those from non-structured grid system and those from the wind tunnel tests. The numerical results and comparisons indicate that the generation of grid systems, the discretization of governing equations and the implementation of the corresponding algorithms are correct and effective. It is also demonstrated that compared with other grid systems, the proposed arbitrary collocated hexahedron grid systems are more accurate and efficient in modeling wind fields around buildings.Most current research on wind-caused interactions between two or more buildings is limited to two same buildings and the effect is also mainly dependent upon the distance-to-height ratio. Using the program WSB, detailed investigations are conducted in this paper on the wind-caused interactions between two low-rising buildings by changing the geometrical configuration of the disturbing building while keeping that of the disturbed building unchanged.