可控流场尺度预混湍流燃烧器及其火焰结构分析

Development of scale-controlled premixed turbulent burner and the flame structure analysis

为了研究单一湍流场参数对预混湍流火焰结构的影响,以及拓宽湍流场的强度和尺度范围,发展了一套可变结构的预混湍流燃烧器。采用恒温型热线风速仪标定流场,得到了一系列湍流参数。流场标定结果表明:该燃烧器能显著拓宽湍流强度和尺度范围,并能利用不同几何结构产生多种可控流场,实现研究单一湍流参数对湍流燃烧速度和火焰结构影响的目的。选用有代表性的15种湍流孔板组合结构,利用OH-PLIF燃烧激光诊断技术,开展了湍流燃烧实验,结果表明:湍流强度的增大(1<u′/S_(L,0)<10)使得湍流火焰分区扩展到了薄层反应区,火焰面破碎程度明显增强,孤岛结构明显增多。高宏观雷诺数下,积分尺度的增长对湍流燃烧速度起抑制作用,可能存在临界宏观雷诺数Rec,能够表现流体惯性力占主导地位的程度,决定积分尺度对湍流燃烧速度的影响效果。积分尺度能量大,扰动能力强,故积分尺度越大,火焰体积越大;但过高的湍流强度会使火焰面褶皱更加剧烈,小尺度叠加在大尺度上的程度增强,最终也使火焰体积显著增大,掩盖了积分尺度对火焰体积的影响,说明积分尺度(表征大尺度)不如湍流强度(表征叠加小尺度的程度)对火焰放热率影响大。

The structure-variable premixed turbulent burner is developed to investigate the effects of single turbulence parameters on flame structure,and to broaden turbulence intensity and scale range.Hot-wire anemometer measurements of cold flow indicate that the burner can utilize different geometry structures to produce scale-controlled flow field and realize the investigation of the effects of single turbulence parameters on flame structure.Fifteen representative structures were selected for the premixed turbulent combustion experiment.OH-PLIF images show that high turbulence intensity enhances flame surface wrinkling,as well as increasing the number of island structures.Data are reported at 1<u′/S L,0<10 for CH 4/air flames with equivalence ratio of 0.7 in the thin reaction zones.Increasing integral scale decreases the turbulent burning velocity at high Reynold number.There may exist a critical Re c which can represent the degree of how inertial forces are dominant to determine the effect of the integral scale on the turbulent burning velocity.Increasing the integral scale can also enlarge the flame volume,due to larger vortex containing higher energy.However,intensive turbulence intensity can wrinkle the flame surface much more remarkably,resulting in superposition of small scales on large scales.Therefore,the increasing turbulence intensity increases the flame volume more significantly,covering up the impact of integral scale on flame volume.integral scale(represent large scale)on the flame heat release rate is less significant than the effect of turbulence intensity(represent superposition degree of small scales on large scales).