矩形自激振荡射流流动与混合特性实验研究

发布时间：2018-03-18 19:56

本文选题：自激振荡射流　切入点：湍流混合　出处：《大连海事大学》2015年硕士论文　论文类型：学位论文

【摘要】：优化喷嘴结构,改善掺混性能,不仅具有深刻的科学意义,而且对于工业燃烧器、混合器、反应器等设备研发具有重要的指导价值。流体射入特定结构的突扩腔体会发生整体低频振荡,称为自激振荡射流。在欧美众多工业应用结果表明,相比于传统多射流燃烧器,自激振荡射流燃烧器可降低NOx排放30%-50%,燃料消耗减少5%-10%。为了进一步优化自激振荡射流燃烧器性能,本文对矩形自激振荡射流进行了实验研究。首先,研究矩形自激振荡射流的流动特性。通过丝带曝光实验、热线实验和烟线实验,测量了不同腔体长度和不同矩形孔口长宽比条件下的射流扩散角、速度场和流场结构。研究发现：长宽比越大,矩形射流二维性越强,越容易产生自激振荡,但是当矩形短边与腔体壁面足够接近时,射流发生偏斜。另外,射流发生振荡还需要在一定的腔体长度范围内。其次,对矩形自激振荡射流的混合特性进行了分析。主要对比分析了射流横截面平均速度、中心线平均速度、脉动速度、湍流度和频谱等湍流统计量。结果表明：相比于自由射流,自激振荡射流的中心线速度衰减更快、扩散角更大、湍流度更高,矩形自激振荡射流的低频能量更多,表明矩形自激振荡射流大尺度混合性能增强。然而通过对比矩形自由射流与自激振荡射流能谱高频区域发现,自激振荡射流小尺度脉动能量更低,表明自激振荡射流小尺度能量被传递到尺度,小尺度混合被抑制。
[Abstract]:Optimizing the nozzle structure and improving the mixing performance not only have profound scientific significance, but also for industrial burners, mixers, The research and development of reactor and other equipment have important guiding value. The whole low frequency oscillation will occur when the fluid is injected into the sudden expansion chamber with a specific structure, which is called self-excited oscillating jet. The results of many industrial applications in Europe and America show that compared with the traditional multi-jet burner, Self-excited oscillating jet burner can reduce NOx emission by 30-50 and fuel consumption by 5- 10. In order to further optimize the performance of self-excited oscillating jet burner, the rectangular self-excited oscillating jet is experimentally studied in this paper. The flow characteristics of rectangular self-excited oscillating jet were studied. The jet diffusion angles were measured under the conditions of different cavity length and different ratio of length to width of rectangular orifice by ribbon exposure test, hot wire experiment and smoke line experiment. Velocity field and flow field structure. It is found that the larger the aspect ratio, the stronger the two-dimensional characteristics of the rectangular jet, and the easier it is to produce self-excited oscillation, but when the rectangular short edge is close enough to the wall of the cavity, the jet deflects. The mixing characteristics of rectangular self-excited oscillating jet are analyzed. The average velocity of cross section, mean velocity of center line, pulsation velocity are compared and analyzed. The results show that compared with the free jet, the central linear velocity of the self-excited oscillating jet attenuates more rapidly, the diffusion angle is larger, the turbulence degree is higher, and the low frequency energy of the rectangular self-excited oscillating jet is higher than that of the free jet. The results show that the large scale mixing energy of the rectangular self-excited oscillating jet is enhanced. However, by comparing the high frequency region of the energy spectrum of the rectangular free jet with the self-excited oscillating jet, it is found that the small scale pulsating energy of the self-excited oscillating jet is lower. It is shown that the small scale energy of the self excited oscillating jet is transferred to the scale and the small scale mixing is suppressed.
【学位授予单位】：大连海事大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U664

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