Study Of Indoor/Outdoor Microbial Aerosol Diffusion And Risk Assessment By The Natural Wind Field

With the frequent outbreak of influenza virus in urban areas, the ecological security of large population density buildings has become increasingly prominent. Three pollutant diffusion models such as k-εRNG,LES and DPM are estabilished. The numerical models are validated by comparing with the experimental data. The indoor and outdoor microbial diffusion is simulated by considering the typical cases of no wind velocity, average wind velocity and natural wind velocity. The results provide the evidence for the nuilding optimization and they are useful for drawing the safety withdrawal plan. The main results are as the follows:First, by comparing with the previous experimental data, the trends of air flow and the changes of contaminant particle concentration can be predicted by the DPM model (the turbulence is enclosed by model of k-εRNG and RNG LES). The indoor air velocity field and the contamination field are validated by the experimental data. The appropriate assumption of collision between the particles and wall is found.Second, the growth curve of common virus and equine influenza virus is solved by the fourth-order Runge-Kutta method. Considering the virus growth curve, the virus diffusion is gained by the estabilished models of k-εRNG,LES and DPM. It is found that the growth curve of the virus affects the concentration area of the microbial contamination and the wind speed field determines the scope of the contaminated areas. The high concentration area is near the source. The most effective way to control the spread of virus is the wind flow field. Virus can spread far with the vortex which has a high concentration and it can lead to a higher risk of secondary infection. The pollution concentration is related to the distance to the source. Reasonable arrangement the buildings according to the wind direction and size can reduce the diffusion of virus.Third, the results of outdoor and indoor-outdoor are simulated by DPM model. The indoor particles spread to outside through the window. Changing the initial particle distribution indoor, it is found that the initial location of virus particles has almost no effect on the transmission and diffusion outdoor and the polluted areas are almost the same.Fourth, the curves of natural wind power spectrum and the velocity field with respect to time are simulated by the improved harmonic synthesis method of FFT. According to the Davenport spectrum, the approximation function of wind velocity field with respect to time is gained to simplify the calculation efforts. Fifth, three cases of wind speed field are considered to simulate the microbial contamination diffusion in outdoor circumstances such as no wind velocity, constant inflow wind velocity and natural inflow wind velocity. When there is no wind outdoor, the spread of pollutants is nearly circular area and the high contamination concentration closes to the surrounding of the buildings and the diffusion area is very small. In the case of natural wind, the virus particles are dispersed faster from the buildings and the contamination concentration is low. However, the large downwind area may face the threat of virus.Finally, the risk assessment is studied by using the numerical simulation results. The location of the greatest risk, the maximum time which the people can stay and the retention capacity of buildings are determined by the criteria concentration.