Temporal evolution of an ignition kernel in a spark ignited turbulent hydrogen–air mixing layer is studied using the large eddy simulation approach with an implicit treatment of the reaction source terms. The applied numerical code is based on a high-order compact difference approximation combined with a weighted essentially non-oscillatory scheme, which provide an accurate resolution of the small scale phenomena. The spark is modelled by an energy deposition model coupled with the enthalpy equation. Since the fuel and oxidiser streams move in the opposite directions the flow is dominated by shear stresses and vortical structures. The ignition follows three different scenarios depending on the spark location. An interaction between the developing flame kernel and large turbulent structure is analysed starting from the energy transfer up to a fully reacting state. The size and shape of the flames are correlated with the initial ignition scenario. A 3D visualisation of the transient position of the flame kernel shows its different spatio-temporal behaviour. It is observed that the flame can stay close to the initial position and spread equally in all directions or it can move far from the initial location and follow the evolving flow field. In the latter scenario two separate sub-stages are convincingly identified. Concerning the ignition probability ( $$P_{ign}$$ ), when the spark is located in the immediate vicinity of the mixing layer, the $$P_{ign}$$ on the fuel-rich side is higher. On the other hand, when the ignition occurs far from the mixing layer, the $$P_{ign}$$ is significantly larger on the lean side. Unlike the local composition the impact of the strain rate of the velocity field was found to have very limited impact on the $$P_{ign}$$ .

中文翻译：

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使用 LES 和层流化学模型研究湍流混合层中的火焰核演化

使用大涡模拟方法对反应源项进行隐式处理，研究了火花点火湍流氢-空气混合层中点火核的时间演变。所应用的数值代码基于高阶紧致差分近似与加权基本非振荡方案相结合，可提供小尺度现象的准确分辨率。火花由能量沉积模型与焓方程相结合建模。由于燃料流和氧化剂流以相反的方向移动，因此流动受剪切应力和涡流结构的支配。根据火花位置的不同，点火遵循三种不同的情况。从能量转移到完全反应状态，分析了发展中的火焰内核和大湍流结构之间的相互作用。火焰的大小和形状与初始点火场景相关。火焰内核瞬态位置的 3D 可视化显示了其不同的时空行为。观察到火焰可以靠近初始位置并在所有方向上均匀传播，或者它可以远离初始位置并跟随演变的流场。在后一种情况下，令人信服地确定了两个独立的子阶段。关于点火概率 ( $$P_{ign}$$ )，当火花位于混合层附近时，富燃料侧的 $$P_{ign}$$ 更高。另一方面，当点火发生在远离混合层时，$P_{ign}$$ 在贫侧明显更大。与局部组成不同，发现速度场的应变率对 $$P_{ign}$$ 的影响非常有限。