Swirling and Impinging Effects in an Annular Nonpremixed Jet Flame
Swirling and Impinging Effects in an Annular Nonpremixed Jet Flame
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DOI：
10.1007/s10494-010-9287-y
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
Xi Jiang;K. Luo;L. D. Goey;R. Bastiaans;J. A. Oijen
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文献类型：
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作者：
Xi Jiang;K. Luo;L. D. Goey;R. Bastiaans;J. A. Oijen
采用直接数值模拟方法研究了旋流和下游壁面约束对环形非预混火焰的影响。采用高阶数值方法和高保真边界条件对变密度流动控制方程和有限速率Arrhenius化学控制方程进行了全三维并行数值模拟。研究了三个旋流数：0(无旋流)、0.4和0.8，而下游壁面约束的影响已经在旋流数0和0.4下进行了考察。结果以瞬时流量和时间平均流量的形式给出，并使用能谱和适当的正交分解(POD)进行了分析。结果表明，旋流对环形非预混火焰的流体动力学行为有显著影响。由于环形结构的喷嘴出口附近的几何回流区(GRZ)、与旋流相关的中心回流区(CRZ)、由于剪切不稳定而形成的射流柱内的非定常涡结构和下游壁面约束之间的相互作用，对火焰的流体动力学行为有很大的影响。根据旋流程度的不同，燃烧器口附近的GRZ和CRZ可能共存，或者一个区域可能被另一个区域淹没。在中等旋流数下，这种共存会导致火焰与燃烧器嘴发生强烈的反应；当旋流数较大时，CRZ区占主导地位，GRZ区占主导地位。观察到旋流流场中存在进动涡核。环形冲击火焰的努塞尔特数分布与圆形冲击火焰的努塞尔数分布不同。POD分析表明，壁面对流场的影响主要与较高的模数有关。
The effects of swirl and downstream wall confinement on an annular nonpremixed flame were investigated using direct numerical simulation (DNS). Fully three-dimensional parallel DNS was performed employing high-order numerical methods and high-fidelity boundary conditions to solve governing equations for variable-density flow and finite-rate Arrhenius chemistry. Three swirl numbers have been examined: 0 (without swirl), 0.4 and 0.8, while the effects of downstream wall confinement have been examined for swirl numbers 0 and 0.4. Results have been presented in terms of instantaneous and time-averaged flow quantities, which have also been analysed using energy spectra and proper orthogonal decomposition (POD). Effects of swirl on the fluid dynamic behaviour of the annular nonpremixed flame were found to be significant. The fluid dynamic behaviour of the flame is greatly affected by the interaction between the geometrical recirculation zone (GRZ) near the jet nozzle exit due to the annular configuration, the central recirculation zone (CRZ) associated with swirl, the unsteady vortical structures in the jet column due to the shear instability, and the downstream wall confinement. Depending on the degree of swirl, the GRZ near the burner mouth and the CRZ may co-exist or one zone may be overwhelmed by another. At a moderate swirl number, the co-existence leads to a flame with strong reaction attached to the burner mouth; while at a high swirl number, the CRZ dominates over the GRZ. The precessing vortex core was observed to exist in the swirling flow fields. The Nusselt number distribution of the annular impinging flames differs from that of round impinging jets. The POD analysis revealed that wall effects on the flow field are mainly associated with the higher mode numbers.