摘要
涡核摆动是旋风分离器流体运动的一种非稳定现象,会对流场造成扰动,导致颗粒返混进而影响分离效率.为了探究涡核摆动的规律和机理,本文对单入口蜗壳式旋风分离器内的流场进行研究,运用PDPA测量流场的基本数据,采用Reynolds应力输运模型对其流动进行数值模拟,并定义旋流不稳定性指数TⅡ来分析流动的不稳定性.结果表明,截面Z/D=0.71上瞬时切向速度波动经Fourier变换后,存在一个集中分布的频率,此频率由涡核摆动导致,而且数值模拟结果与实验测量数据吻合较好。通过对涡核中心的运动轨迹分析,发现在整个旋风分离器空间内部都存在涡核摆动现象;在同一时刻,各个截面的涡核中心偏离几何中心的情况并不相同,涡核区域也不一致;各个截面的涡核中心的连线并不在一个平面或者直线上,而是摆动的。此外,分析TⅡ曲线发现气流从不对称的入口结构进入旋风分离器内部,涡核中心开始偏离几何中心,不稳定性逐渐扩大;随着旋流运动向下,入口结构不对称对旋流的影响变小,不稳定性又逐渐减小;流动最终在Z/D=8之后趋于稳定.
Vortex core oscillation is a kind of unstable phenomenon in cyclone separator. Which can cause the backmixing of particles and affect the separation efficiency. To explore its mechanism, an experimental investigation was conducted for a volute cyclone with single inlet. The basic data of flow field would be measured by Phase Doppler Particle Analyzer(PDPA). Secondly, the numerical simulation data should be carried by Reynolds Stress model(RSM). Finally, an index(Time instability index) was defined to analyze the instability of flow. The results showed that tangential velocity of Z/D = 0.71 could obtain an obvious fundamental frequency by Fourier transform technique, which was caused by vortex core oscillation. The calculation results of frequency of Z/D = 0.71 were in good agreement with the experimental measurement data. Through the analysis of vortex core center, the vortex core oscillation phenomenon was found to exist in the whole space within cyclone separator.At the same time, cases of the vortex core center deviating from the geometric center in different section were not the same. The curve of vortex core centers in each section was not in a plane or a straight line, but swing. Furthermore, the flow fluctuation was large in the upper region of cyclone because of the non-axisymmetry of entrance while the flow tended to stable afterZ/D = 8.
引文
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