Modeling nongray gas-phase and soot radiation in luminous turbulent nonpremixed jet flames
Modeling nongray gas-phase and soot radiation in luminous turbulent nonpremixed jet flames
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DOI：
10.1080/13647830500255551
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发表时间：
2005-08
影响因子：
1.3
通讯作者：
L. Wang;M. Modest;D. Haworth;S. Turns
中科院分区：
文献类型：
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作者：
L. Wang;M. Modest;D. Haworth;S. Turns
辐射换热模拟在处理气相物质和烟尘颗粒的非灰色辐射方面已经取得了很大进展，而湍流火焰模拟中的辐射模拟仍处于起步阶段。为了缩小这一差距，本文将最新的气相和烟尘辐射模型引入湍流火焰模拟中。将全光谱k分布方法(Med，M.F.，2003，Journal of Quantity Spectrtics&Radiative Transfer，76，69-83)实现到用于非灰色辐射模拟的三维非结构CFD程序中。基于建立的窄带k分布数据库，构造了包括非灰色碳烟颗粒在内的混合物全光谱k分布，并在CFD模拟中采用了一种有效的构造方案。详细的反应机理包括NOx和碳烟动力学被用来预测火焰结构，碳烟模型被用来确定碳烟颗粒的尺寸分布。采用球谐P_1近似求解辐射传递方程。模拟了一种富氧、湍动、非预混的射流火焰，其特点是大量的气相辐射物质和碳烟颗粒。在煤烟火焰模拟中，非灰色烟尘模型比非灰色气体模型更重要，灰色烟尘模型会产生较大的误差。烟尘的非灰色处理对上游和火焰尖端区域的火焰温度有很大影响，对于准确预测NO是必不可少的。然而，气体的非灰色处理对上游火焰温度的影响很小，因此对无预测的影响很小。在烟尘浓度较小的下游区域，非灰色烟尘辐射对火焰温度的影响也很大。讨论了喷流火焰形状的P1近似的局限性；对于高度各向异性的辐射场，例如具有局部、近不透明碳烟区域的火焰中的辐射场，P1近似在计算的辐射热流的空间分布中产生了很大的误差。
Much progress has been made in radiative heat transfer modeling with respect to treatment of nongray radiation from both gas-phase species and soot particles, while radiation modeling in turbulent flame simulations is still in its infancy. Aiming at reducing this gap, this paper introduces state-of-the-art models of gas-phase and soot radiation to turbulent flame simulations. The full-spectrum k-distribution method (Modest, M.F., 2003, Journal of Quantitative Spectroscopy & Radiative Transfer, 76, 69–83) is implemented into a three-dimensional unstructured CFD code for nongray radiation modeling. The mixture full-spectrum k-distributions including nongray absorbing soot particles are constructed from a narrow-band k-distribution database created for individual gas-phase species, and an efficient scheme is employed for their construction in CFD simulations. A detailed reaction mechanism including NO x and soot kinetics is used to predict flame structure, and a detailed soot model using a method of moments is employed to determine soot particle size distributions. A spherical-harmonic P1 approximation is invoked to solve the radiative transfer equation. An oxygen-enriched, turbulent, nonpremixed jet flame is simulated, which features large concentrations of gas-phase radiating species and soot particles. Nongray soot modeling is shown to be of greater importance than nongray gas modeling in sooty flame simulations, with gray soot models producing large errors. The nongray treatment of soot strongly influences flame temperatures in the upstream and the flame-tip region and is essential for accurate predictions of NO. The nongray treatment of gases, however, weakly influences upstream flame temperatures and, therefore, has only a small effect on NO predictions. The effect of nongray soot radiation on flame temperature is also substantial in downstream regions where the soot concentration is small. Limitations of the P1 approximation are discussed for the jet flame configuration; the P1 approximation yields large errors in the spatial distribution of the computed radiative heat flux for highly anisotropic radiation fields such as those in flames with localized, near-opaque soot regions.