College of Modern Logistics, Shanxi Vocational University of Engineering Science and Technology, Taiyuan, Shanxi, China.
College of Environmental Science and Engineering, Taiyuan University of Technology, Taiyuan, Shanxi, China.
PLoS One. 2024 Jun 24;19(6):e0305739. doi: 10.1371/journal.pone.0305739. eCollection 2024.
The thermal effect mainly includes boundary temperature stratification and the local thermal effect. The combined effect of these factors on flow and dispersion in a bi-dimensional canyon was investigated by the RANS and LES methods to evaluate their performance. The results, including the flow field, turbulent kinetic energy, temperature, heat flux, pollutant concentration and fluxes, were compared with the data from wind tunnel experiments. The comparison results showed that the RANS method severely overestimated the impact of windward heating on the flow in the canyon because of the lack of simulated flow separation ability and the limitation of the Boussinesq model, leading to an incorrect flow field and an incorrect temperature and concentration. In contrast, LES performed better mainly because of its ability to simulate flow separation. LES regenerated the right vortexes, flow field and low wind velocity. LES slightly overestimates the overall temperature in the canyon because heat exchange is eliminated in LES but difficult to avoid in the experiment. The difference in the air exchange rate at the roof level between the LES and wind tunnel data was no more than 5%, and the pollutant concentration distribution of the LES was almost the same as that of the experiments. This work emphasizes that the RANS method has limited ability to simulate flow and dispersion when the thermal effect is considered even at a reduced-scale, while LES can simulate the combined effects of incoming flow temperature stratification and local thermal effects. It is therefore suggested that if computing resources are limited and the temperature difference is not large, a steady-state calculation RANS can be used. Otherwise, LES must be performed.
热效应主要包括边界温度分层和局部热效应。通过 RANS 和 LES 方法研究了这些因素对二维峡谷内流动和扩散的综合影响，以评估它们的性能。将包括流场、湍流动能、温度、热通量、污染物浓度和通量在内的结果与风洞实验数据进行了比较。比较结果表明，由于缺乏模拟流分离能力和 Boussinesq 模型的限制，RANS 方法严重高估了迎风加热对峡谷内流动的影响，导致流场和温度及浓度不正确。相比之下，LES 表现更好，主要是因为它具有模拟流分离的能力。LES 重新生成了正确的漩涡、流场和低风速。LES 略微高估了峡谷内的整体温度，因为在 LES 中消除了热交换，但在实验中很难避免。LES 和风洞数据在屋顶层的空气交换率之间的差异不超过 5%，并且 LES 的污染物浓度分布几乎与实验相同。这项工作强调，即使在缩小规模的情况下，当考虑热效应时，RANS 方法模拟流动和扩散的能力有限，而 LES 可以模拟来流温度分层和局部热效应的综合影响。因此建议，如果计算资源有限且温差不大，可以使用稳态计算 RANS；否则，必须进行 LES。
