【作者】 杜一庆；

【导师】 钱壬章；

【作者基本信息】 华中科技大学 ， 工程热物理， 2005， 博士

【摘要】 开缝钝体能否成功地用于加力燃烧室稳定器,两个重要指标分别是阻力特性和火焰稳定性,即要求总压损失尽可能小的同时,维持在高温高速条件下的火焰稳定。开缝钝体的火焰稳定性能和阻力特性与尾迹中具有大涡尺度的拟序结构密切相关,目前对这方面的认识还较欠缺。因此,本文的重点是采取数值模拟和实验研究来解析钝体尾迹的拟序结构和旋涡脱落动力学机制,并对其火焰稳定机理进行了分析。这些研究旨在提供优化开缝钝体的基础理论或基础数据,为高速情况下的实验研究打下基础。在雷诺数Re 为470000 条件下利用RNG k–ε模型对开缝三角形钝体和不同V 形钝体火焰稳定器的尾迹进行数值模拟。模拟结果与已有的实验结果吻合。将大涡模拟与RNG k–ε模型计算结果比较,也证实RNG k–ε模型适合于模拟通道内的开缝钝体尾流。从模拟结果得出,开缝V 形钝体在缝宽率为36%时,其火焰稳定能力和阻力特性综合性能达到最佳。分析了尾迹的拟序结构并将其描述为:偏向一侧的中缝流将近尾分成主回流区和次回流区,主回流区的旋涡脱落激发扰动引起近尾的绝对不稳定。首次提出单涡突然置于两剪切层间的旋涡脱落动力学机理。采用常规单点测量方法在开式风洞中对不同开缝V 形钝体进行冷态实验,测量总压损失系数和反流区大小,实验结果验证了数值模拟结果。利用激光粒子测速在闭式风洞中对不同缝宽率的开缝钝体和相同缝宽率情况下不同形式的开缝钝体近尾结构进行了测量。研究不同的开缝钝体近尾湍流剪切流的统计特性和结构形态,及其动力学机制,如涡量的聚集、输运和演化等。首次提出旋涡脱落特征尺度来定量分析非稳态尾流,是一次意义重大的钝体绕流理论和实验分析方法上的创新。同时结合全程平均分析法,对大量的实验数据进行整理来定量比较不同钝体的尾迹结构,对开缝钝体的火焰稳定特性和阻力特性进行预测。结合开缝钝体冷态流场分析,采用非定常方法对其火焰稳定机理进行了分析。研究首次发现,中缝流的存在使近尾中的湍能分布集中度下降,却增大了旋涡脱落特征更多还原

【Abstract】 Whether the slitted bluff body can be successfully used as flameholder in aircraft afterburner or not depends on its drag and flameholding ability, which requires less drag and better flame stabilization at high temperature and high speed. These characteristics intimately relate to the coherent structure of large vortex over the slitted bluff body, about which numerous questions remain. The focus of present paper is explaining the coherent structure and vortex shedding dynamics in the wake over bluff body, and studying the flameholding mechanism numerically and experimentally. The basic theory or data to optimize slitted bluff body will be proposed through the investigation, which is fundamental to carry on further experiment at high speed. The wake regions after a triangle bluff body and different V shape bluff bodies were investigated numerically using the RNG k -εmodel at Reynolds number of 470000. The numerical results are of good agreement with the previous experiments. The comparison between RNG k -εmodel and large eddy simulation also indicates that RNG k -εmodel is adequate in computing the bluff body flow. The evidence shows that the V shape slitted bluff body has the best flameholding ability and the lowest drag at a gap ratio of 36%. The evolution of the coherent structure over slitted bluff body was investigated: The coherent structure is divided by the gap flow, which deflects to one side, into two zones called the primary recirculation zone and the secondary recirculation zone, vortex shedding in the primary recirculation zone stimulates absolute instability in the near wake. To explain the vortex shedding, a mechanism that single vortex of large dimension suddenly immerses between two shear layers was proposed. Cold state experiment in an open tunnel was carried out to measure the total pressure loss coefficient and minus x-component velocity zone, the experiment results confirm the observation from the numerical study. Particle image velocimetry measurements in a close wind tunnel were also carried out to investigate the wake structure after a slitted bluff body with different gap ratios and different slitted bluff bodies with the same gap ratio. The researcher investigated the statistical character and structure of the turbulent shear flow of the near wake, and its dynamic mechanism like vorticity concentration, transport and evolution et al. Of particular significance to the theory in flow over bluff body and the experiment analysis methods was the definition of vortex shedding character dimension, which was first proposed by the researcher to analyze the time-dependent wake flow quantitatively. Using the ensemble-averaged mean, flow structure comparison among different bluff bodies was made by analyzing the experiment data, the flameholding and drag characteristics of slitted bluff body were forecasted. The flameholding mechanism was studied in time-dependent viewpoint on the basis of the investigation on wake structure in cold state. The researcher discovered that the gap flow makes the turbulent energy distribution wider, on the other hand, makes the vortex shedding character dimension longer, prolongs the elapsed time between the fuel gas in gap flow and shear layers gets in and out the recirculation zone, creates favourable condition for flame stabilization in the gap flow, and intensifys the firing support between the two shear layers. All the evidence proves that the slitted bluff body is a high efficiency flameholder with low drag. The flameholding mechanism was confirmed by the combustion experiment at low speed. Using the equilibrium state concept, topologic method and energy method, the transition of the wake over slitted bluff body was investigated, which was confirmed by the particle image velocimetry measurements, the nonlinear dynamics and vortex evolution mechanism in wake transition from layer flow to turbulent flow was proposed.更多还原