Flame- and flow-conditioned vorticity transport in premixed swirl combustion
Flame- and flow-conditioned vorticity transport in premixed swirl combustion
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预混旋流燃烧中的火焰和流动调节涡量传递
DOI：
10.1016/j.proci.2020.06.211
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
A. Steinberg
中科院分区：
文献类型：
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作者：
A. Kazbekov;A. Steinberg
本文介绍了在Karlovitz数为20 ~ 50的预混旋流燃烧中火焰诱导涡度拟能输运的实验分析。这样的火焰拥有一个大尺度的压力场，除了与小尺度湍流涡旋相关的压力场之外，还可以与密度梯度相互作用，产生斜压扭矩。同时层析粒子图像测速和甲醛平面激光诱导荧光测量被用来获得高分辨率的速度和渐进变量场。这使得统计评估的各种条款拟能运输方程。小规模和大规模的压力梯度的影响进行评估，通过调节斜压扭矩的瞬时火焰前内的流体的位置，在火焰刷，轴向燃烧器内。在所有的条件下研究，斜压扭矩是一个显着的贡献涡度拟能运输，具有相当的幅度涡拉伸和粘性扩散。涡度拟能衰减和斜压扭矩的产生倾向于分别发生在瞬时火焰表面的反应物和产物侧。然而，斜压扭矩的值同样强烈地依赖于燃烧室中的位置。因此，小尺度和大尺度气压场都可以通过斜压扭矩导致显着的涡度拟能变化。提出了一种尺度来量化涡旋诱导的压力场对斜压扭矩涡度拟能产生的重要性;结果表明，涡旋诱导的压力场随着涡旋数的增加而增加，随着Damköhler数的减少而增加。这证明了火焰诱导的涡动力学在旋流燃烧中是重要的，并且大尺度几何形状相关的流场可以影响火焰产生的湍流。
This paper presents an experimental analysis of flame-induced enstrophy transport in premixed swirl combustion at Karlovitz numbers between 20 and 50. Such flames possess a large-scale pressure field that – in addition to the pressure fields associated with small-scale turbulent vortices – can interact with density gradients to produce baroclinic torque. Simultaneous tomographic particle image velocimetry and formaldehyde planar laser induced fluorescence measurements are used to obtain high-resolution velocity and progress-variable fields. This allows statistical evaluation of the various terms in the enstrophy transport equation. The impact of small- and large-scale pressure gradients is assessed by conditioning the baroclinic torque on the position of the fluid within the instantaneous flame front, within the flame brush, and axially within the combustor. At all conditions studied, the baroclinic torque was a significant contributor to enstrophy transport, with a comparable magnitude to vortex stretching and viscous diffusion. Enstrophy attenuation and production by baroclinic torque tended to occur towards the reactant and product sides of the instantaneous flame surface, respectively. However, the value of the baroclinic torque also depended equally strongly on the position in the combustor. Hence, both small- and large-scale pressure fields can result in significant enstrophy changes through baroclinic torque. A scaling is proposed to quantify the significance of swirl-induced pressure field on baroclinic torque enstrophy production; it is shown to increase with increasing swirl number and decreasing Damköhler numbers. This is evidence both that flame-induced vorticity dynamics are significant in swirl combustion, and that large-scale geometry-dependent flow fields can impact flame-generated turbulence.