Scalar Gradient and Strain Rate Statistics in Oblique Premixed Flame-Wall Interaction Within Turbulent Channel Flows
Scalar Gradient and Strain Rate Statistics in Oblique Premixed Flame-Wall Interaction Within Turbulent Channel Flows
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DOI：
10.1007/s10494-020-00169-3
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发表时间：
2020-06-15
影响因子：
2.4
通讯作者：
Klein, Markus
中科院分区：
文献类型：
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作者：
Ahmed, Umair;Chakraborty, Nilanjan;Klein, Markus
在绝热和等温壁边界条件下，使用单步化学对 V 型火焰与完全发展的湍流通道流中的化学惰性壁相互作用进行了三维直接数值模拟。这些模拟代表了大气条件下单位路易斯数的化学计量甲烷-空气混合物。非反应通道中的湍流代表基于雷诺数Re-tau=110的摩擦速度。对于不同的壁边界条件，进度变量、温度和密度的平均值的统计行为存在差异。研究发现，与壁相互作用的倾斜火焰的平均位置受到所使用的壁边界条件的选择的影响。通过分析表面密度函数 (SDF) 和应变率的统计行为（控制 SDF 的演化），研究了这些差异对火焰动力学的影响。 SDF 的平均变化和火焰位移速度受到边界层粘性子层区域内壁边界条件的强烈影响。发现法向应变率和切向应变率的行为不仅受到壁边界条件差异的影响，而且还受到距壁距离的影响。不同壁边界条件和壁距离的位移速度统计差异会影响由于火焰传播和曲率拉伸而产生的法向应变率的行为。近壁区域SDF行为的变化可以通过不同壁边界条件和壁法向距离下进度变量等值面所经历的有效法向应变率的统计来解释。
Three-dimensional direct numerical simulations of V-flames interacting with chemically inert walls in a fully developed turbulent channel flow have been performed under adiabatic and isothermal wall boundary conditions using single-step chemistry. These simulations are representative of stoichiometric methane-air mixture at unity Lewis number under atmospheric conditions. The turbulence in the non-reacting channel is representative of the friction velocity based Reynolds number Re-tau=110. Differences in the statistical behaviours of the mean values of progress variable, temperature, and density have been reported for different wall boundary conditions. It is found that the mean location of the oblique flame interacting with the wall is affected by the choice of the wall boundary condition used. The influence of these differences on the flame dynamics is investigated by analysing the statistical behaviours of the surface density function (SDF) and the strain rates, which govern the evolution of the SDF. The mean variation of the SDF and the flame displacement speed are strongly affected by the wall boundary condition within the viscous sub-layer region of the boundary layer. The behaviours of the normal and tangential strain rates are found to be influenced by not only the differences in the wall boundary conditions, but also by the distance from the wall. The differences in the displacement speed statistics for different wall boundary conditions and wall distance affect the behaviours of the normal strain rate arising due to flame propagation and curvature stretch. The changes in the SDF behaviour in the near wall region have been explained in terms of the statistics of effective normal strain rate experienced by the progress variable iso-surfaces under different wall boundary conditions and wall normal distances.