Abstract Wildland fires can take different forms such as surface fire or an elevated crown fire or combination of both. Crown fires are normally originated from surface fires spreading either along the bark of the tree trunks or direct flame contact to low branches with leaves and needles. In the past, surface fire (grassfire) spread simulations were conducted using physics-based models with fidelity. Here, we firstly seek numerically converged results for the burning of a single tree. Previously, numerical convergence for such physics-based fire simulations has been elusive. Subsequently, the linear and Arrhenius thermal degradation sub-models are appraised. For both thermal degradation sub-models grid convergence of the mass-loss rate is achieved with a 50 mm grid. The grid converged simulations also agree with experimental results of a single burning Douglas fir tree. A fire in a modelled tree plantation is then simulated using the linear thermal degradation sub-model. The aim of this part is twofold: one to demonstrate a good modelling practice; and secondly to assess the model capability to simulate transitioning from a forest floor fire to a crown fire leading to a quasi-steady rate of spread. The Kolmogorov–Smirnov test is used to rigorously demonstrate that the simulations on different grid and domain sizes have converged — that is, the results have become independent of the numerical parameters imposed upon the simulation. A physics-based model reproduces many observed features of surface fire to forest fire transition. The crown fire propagates with a quasi-steady rate-of-spread after an initial development period. Analysis of the volumetric heat release rate shows that a surface fire propagates under the crown fire and supplies energy to support the burning of the crown. Overall many features are qualitatively in agreement with other tree and crown fire studies.

中文翻译：

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使用基于物理的模型对树木火灾和从森林地面过渡到树冠的火灾进行建模

摘要 野火可以采取不同的形式，例如地表火灾或高架树冠火灾或两者的组合。树冠火灾通常源于沿树干树皮蔓延的表面火灾，或直接接触带有树叶和针叶的低矮树枝的火焰。过去，地表火灾（草火）蔓延模拟是使用基于物理的保真模型进行的。在这里，我们首先寻求燃烧一棵树的数值收敛结果。以前，这种基于物理的火灾模拟的数值收敛一直难以捉摸。随后，对线性和 Arrhenius 热降解子模型进行了评估。对于两个热降解子模型，质量损失率的网格收敛是通过 50 mm 网格实现的。网格收敛模拟也与单个燃烧的花旗松树的实验结果一致。然后使用线性热降解子模型模拟模拟树木种植园中的火灾。这部分的目的有两个：一是展示良好的建模实践；其次，评估模型模拟从森林地面火灾到树冠火灾导致准稳定蔓延速度的能力。Kolmogorov-Smirnov 检验用于严格证明在不同网格和域大小上的模拟已经收敛——也就是说，结果已经独立于强加在模拟上的数值参数。一个基于物理的模型再现了许多观察到的地表火灾到森林火灾转变的特征。在初始发展期之后，冠火以准稳定的传播率传播。体积放热率分析表明，表面火在冠火下传播并提供能量以支持冠部燃烧。总的来说，许多特征与其他树木和树冠火灾研究在性质上是一致的。