It is well-known that the correct modeling of the plume rise is fundamental for a proper description of pollutants dispersion, especially for highly buoyant plumes like those emitted by wildfires. In this work, we want to investigate the role of the drag coefficient () in our plume rise scheme. We evaluate different formulations taken from the literature and suggest the best option for the plume rise scheme embedded in the Lagrangian Stochastic model SPRAY-WEB. As a matter of fact, previous works on plume rise models are based on the drag coefficient which is a quantity that should be determined. There is not a general consensus on the best values for . Some values suggested in the literature are simply constants that do not directly depend on the meteorological and turbulent variables. In order to evaluate the model performances obtained using different formulations we simulate a field experiment, carried out in August 2013 in Idaho (USA), in which prescribed fires were observed and the physical and chemical parameters were measured. As a matter of fact, plumes emitted from fires are affected by strong buoyancy and very low or even negligible initial vertical momentum. These conditions are very different from traditional plumes from stacks for which the classical plume rise models are built. For this reason, the case studies chosen for the tests are very challenging and they allow us to assess the scheme here proposed in the best way. Comparison among the results obtained with different parameterizations are presented and discussed. Three of the four models tested derive from an extension of the Stokes’ law; the fourth one is a more refined model derived from the Shanks transformation of the Goldstein series. This last model seems to give better results as regards the maximum height of the plume, but is the one that underestimates most CO concentrations.

中文翻译：

---

火灾烟气扩散烟羽上升模型中湍流相关阻力系数的评估

众所周知，羽流上升的正确建模对于正确描述污染物扩散至关重要，特别是对于野火排放的高浮力羽流而言。在这项工作中，我们想要研究阻力系数 () 在我们的羽流上升方案中的作用。我们评估了文献中的不同公式，并提出了嵌入拉格朗日随机模型 SPRAY-WEB 中的羽流上升方案的最佳选择。事实上，先前关于羽流上升模型的工作都是基于阻力系数，这是一个需要确定的量。对于 的最佳值尚未达成普遍共识。文献中建议的一些值只是常数，不直接取决于气象和湍流变量。为了评估使用不同配方获得的模型性能，我们模拟了 2013 年 8 月在美国爱达荷州进行的现场实验，其中观察了规定的火灾并测量了物理和化学参数。事实上，火灾喷出的羽流受到强大的浮力和非常低甚至可以忽略不计的初始垂直动量的影响。这些条件与构建经典羽流上升模型所针对的烟囱中的传统羽流有很大不同。因此，为测试选择的案例研究非常具有挑战性，它们使我们能够以最佳方式评估此处提出的方案。介绍并讨论了使用不同参数化获得的结果之间的比较。所测试的四个模型中的三个源自斯托克斯定律的扩展；第四个是由Goldstein级数的Shanks变换衍生的更精致的模型。最后一个模型似乎在羽流最大高度方面给出了更好的结果，但低估了大多数二氧化碳浓度。