The present paper reports on the investigation of turbulent transport and fuel mixing under nonreacting conditions for a model gas-turbine swirl burner based on a design by Turbomeca. Two regimes of fuel (methane with acetone vapor) injection are compared. Specifically, the injection between the vanes of the radial swirler organizes lean, well-premixed combustion in a primary zone. The fuel supply as a central jet from the swirler’s centre-body provides a pilot flame. A combination of stereoscopic PIV and acetone PLIF systems is used to measure the velocity and concentration fields in the flows with a Reynolds number of 3 × 10⁴. The effect of the central jet density is tested by replacing methane with air and neon. The data are processed using the POD method to extract coherent flow structures and quantify large-scale variations in concentration produced by them. In both cases, the flow dynamics were associated with the movement of large-scale vortex structures in the inner and outer mixing layers. The coherent flow fluctuations provide a substantial contribution to the turbulent transport, which locally exceeds 60% for the Reynolds shear stresses and Reynolds fluxes. The mixing is analysed based on the local probability of the fuel concentration pulsations. The probability distributions for the coherent and stochastic components of the pulsations are considered separately. For the premixed operation regime, the variation in the local equivalence ratio at the nozzle exit of the swirl burner reached 35% with the contribution of coherent pulsations up to 7%. In contrast, the large-scale vortex structures for the diffusion pilot jet flame primarily contributed to the advection of the fuel but not mixing. This paper provides relevant data for validating numerical methods for simulating unsteady turbulent mixing in swirl combustors.

Graphic abstract

中文翻译：

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PIV / PLIF研究模型燃气轮机燃烧室后面的不稳定湍流和混合

本文报道了基于Turbomeca设计的模型燃气轮机旋流燃烧器在非反应条件下的湍流传输和燃料混合的研究。比较了两种燃料喷射方式（甲烷和丙酮蒸气）。具体而言，径向旋流器叶片之间的喷射在主要区域组织了稀薄且预混合良好的燃烧。来自旋流器中心体的作为中心射流的燃料供应提供了引燃火焰。立体PIV和丙酮PLIF系统的组合用于测量雷诺数为3×10 ⁴的流中的速度场和浓度场。通过用空气和氖气替代甲烷来测试中央射流密度的影响。使用POD方法对数据进行处理，以提取相干的流动结构并量化由它们产生的浓度的大规模变化。在这两种情况下，流动动力学都与内部和外部混合层中大规模旋涡结构的运动有关。相干流动波动为湍流输送提供了重要的贡献，对于雷诺剪切应力和雷诺通量，湍流输送局部超过60％。基于燃料浓度脉动的局部概率来分析混合。分别考虑脉动的相干分量和随机分量的概率分布。对于预混操作方案，在旋流燃烧器的喷嘴出口处的局部当量比的变化达到35％，相干脉动的贡献高达7％。相比之下，用于扩散引燃喷射火焰的大规模涡旋结构主要有助于燃料的平流，但没有促进混合。本文提供了相关数据，以验证用于模拟旋流燃烧室中非稳态湍流混合的数值方法。

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