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To prevent the accidental release of toxic gases in urban environments, it is imperative to measure the concentration field quickly and accurately. The response factor method (RFM) based on the linear response relationship between the sources and the sensors for a steady flow field and a fixed pollution source location yields good results in concentration calculations after pollutant release. It is necessary to convolve the response factor with the release function to calculate the concentration of different pollutant-release conditions. RFM can save considerable calculation time. However, current studies primarily emphasize indoor environments and lack outdoor environment simulations. Thus, we aim to address the problem of using RFM to simulate the concentration when time-varying pollution release occurs around buildings.
To confirm the reliability of the simulation results, two examples of wind tunnel data (CEDVAL experiment No. A1-5 an isolated building, and No. B1-1 building arrays) were simulated under the same conditions, and the velocity profile results were consistent. RFM consisted of the following steps: (1) The calculation domain was constructed, and the flow field was solved in the steady state. (2) The concentration field under the pulse pollutant release was solved in the transient state, the time series of the concentration response factor was obtained, and the component transfer matrix A represented by the response factor sequence was constructed. (3) The concentration at any time was calculated from the time series of the component transfer matrix A and the release intensity. RFM and computational fluid mechanics (CFD) transient simulation method were employed to simulate three types of pollutant-release scenarios: constant, periodic, and triangular releases. Based on the structural characteristics of the flow field around buildings, sensor positions of different heights and distances were selected for comparison. Next, the RFM and CFD results were compared using the commonly used statistical indexes: fractional bias (FB), normalized mean square error (NMSE), and the ratio between ratio 2 (FAC2).
(1) The results reveal that the concentration RFM can effectively simulate the diffusion of pollutants around buildings. The variation trend of the concentration field aligns with the transient simulation results of CFD, and the FAC2 value is>0.95. The running time of this method is 1/30 of the CFD transient simulation. (2) For the time-varying pollution-release function, RFM can simulate the concentration field well and the concentration at any time in the process well.
In this paper, RFM is applied to the case of pollutant diffusion around urban buildings. Compared with the CFD transient simulation results, the method can be applied to the rapid simulation of outdoor pollutant concentration and the influence of different time-varying pollution source release functions can be obtained. These results provide a foundation for the rapid calculation of the concentrations of multiple cases of pollutant diffusion around buildings using RFM.
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