Application Of Zero-Equation Model In Outdoor Air Flow Around Building Simulation

The research on the outdoor micro-climate is very important for two reasons. First, the outdoor micro-climate determines the comfort and air quality of the outdoor environment. Second it has great influence on energy consumption and natural ventilation in building. Since the residential area in China is increasing quickly, a quick way to simulate the outdoor environment of the residential area becomes essential. Currently, k-εmodel and relevant improved models, which require significant amount of computation time, are the most widely used turbulence model in outdoor simulation.From the perspective of engineering application, this paper studies the interaction between the buildings and the coming air flow through literature review and by analyzing the results of air flow simulation around the buildings using k-εmodel. It is found that the result of the traditional mix-length model and the MIT zero-equation model in the simulation of the flow around the buildings are not satisfactory. There are two reasons. First, the definition of traditional mix-length is not suitable for the flow around the building. Second, the MIT zero-equation model would underestimate the turbulent viscosity coefficient in the shadow area behind the building.Through qualitative analysis on the distribution of the turbulence viscosity coefficient in the simulation of flow around the building in the atmospheric boundary using k-εmodel, and the impact on the mix-length by the buildings, the author proposes two new two-layer zero-equation models: mix-length model for the inner form and MIT zero-equation model for the outer form. In this paper, a large number of simulation results of the new zero-equation model and the comparisons with k-εmodel are provided to illustrate the application of the new zero-equation model in the outdoor rounding flow simulation. The first new zero-equation model is suitable when the heights and the rates of length/height of the buildings are similar, such as one similar residential, and it will save commuting consumption and get results close to the traditional k-εmodel. The second new zero-equation model is suitable for more complex conditions, and it can get satisfactory results conveniently and quickly. In the last section of this paper, the second zero-equation model is applied to a residential case study. The results are compared with the measured value and proved to be consistent. The simulated wind directions are fully consistent with the k-εmodel results, and same with most of the measured sample points.The calculated speed of outdoor rounding flow simulation is hence possible to speed up. New zero-equation models in this paper are expected to be widely applied in engineering projects.