# Development of Building CFD Model Design Process Based on BIM
## 1 Introduction  
Computational fluid dynamics (CFD) is a fast and economic analysis method to analyze complex fluid flows through numerical analysis [1]. Computational Fluid Dynamics (CFD) enables various simulations related to the fluid flows of complex building shapes. Therefore, CFD is emerging as an effective tool for evaluating ventilation, energy performance, design, and stability in the field of architecture [2, 3]. CFD enables the analysis of various shapes and environmental conditions through numerical analysis, so it is more productive than traditional analysis methods [4]. Meanwhile, appropriate CFD models need to be designed by considering flow characteristics and environmental conditions to obtain reliable results [5]. CFD model design, a pre-processing process for CFD analysis, includes designing the geometry model, designing the grid model, and setting the boundary conditions. Each process is a significant factor in determining the accuracy of CFD simulation results. Moreover, pre-processing is the most time- consuming process for flow simulation [6]. Therefore, it is necessary to design the appropriate CFD model. Recently, Building Information Modeling (BIM) has emerged as a key modeling technology in the field of architecture, due to the diversification and vitalization of technologies [7]. BIM contains geometric and attributes information about buildings, which provide the physical and functional characteristics of buildings [8]. The data in BIM models can be used in various fields. BIM is used to manage the design, manufacture, and construction processes and to control the quality of construction [9, 10, 11, 12]. The building information in BIM is also applied to research related to disaster and fire analysis [13, 14, 15]. In particular, it can be used in the field of simulation that requires 3D building model design [16, 17, 18]. The data embedded in BIM models can be used for designing models or setting the environmentalconditions of simulations, such as Building Energy Simulation (BES) or CFD [19]. BIM contains the information required for building energy performance analysis. Therefore, using the BIM model can save considerable time and effort in model design, and reduce data inconsistencies and human errors [20]. Due to these advantages, various studies coupled BES with BIM. In existing studies, data conversion has been performed on both geometry and attribute data. On the other hand, most CFD research only use BIM the models for sharing geometry data. In addition to geometric data, BIM also contains attribute data that can be used for setting boundary conditions, enabling efficient model design [21]. Therefore, it is necessary to integrate attribute data in addition to geometry data. CFD divides the space to be analyzed into a finite number of grids to predict the flow of fluids, so grid design is important for accurate analysis results [22]. Therefore, a high-quality grid model design is necessary. To this end, an optimization process for geometry and grid models should be conducted. There are difficulties in creating grids for complex shapes, which often lead to low grid quality. Hence, it is necessary to improve grid quality through geometry simplification [23]. However, geometry simplification takes a considerable amount of time because it entails much manual work [6]. Grid optimization also requires considerable trial and error to improve grid quality, and therefore, is a time-consuming process. In addition, geometry and grid optimization usually rely on user experience and judgment because there are no standardized methods or procedures. Meanwhile, BIM models contain detailed geometric characteristics of all objects. If it is applied to CFD models without optimization, it may be impossible to generate a grid, or a poor grid may be derived, resulting in a decrease in analysis accuracy. Therefore, optimization of geometry and grid models should also be considered to integrate BIM and CFD.