Mixing and scalar dissipation rate in a decaying jet
Mixing and scalar dissipation rate in a decaying jet
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衰减射流中的混合和标量耗散率
DOI：
10.1016/j.proci.2020.08.042
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发表时间：
2021
影响因子：
3.4
通讯作者：
Hua X
中科院分区：
文献类型：
--
作者：
Hua X
通过测量衰变、等温、湍流气体射流中的摩尔分数和标量耗散率 (SDR) 来量化衰变射流 (Re=50,000) 中混合场的时间发展。通过使用丙酮的平面激光诱导荧光来测量二维标量场，并且通过适当的图像处理，这允许使用两个平面内分量来估计 SDR，误差在 16% 之内。报告了喷射结束后下游无量纲距离最多 7 个喷嘴出口直径和 35 个出口流动时间尺度的摩尔分数的瞬时和平均分布。随着最后一个均匀出口浓度 (UEC) 轮廓核心远离喷嘴出口的平流，在衰减射流的后缘处出现了一个弱浓度区域。在拉格朗日参考系中进行的估计表明，喷射结束（AEI）后，喷射流的后缘变得比稳定状态下更快，从而证实了“夹带波”的存在。不同站点和时间 AEI 的 2D SDR 归一化概率密度函数与低 SDR 值和高 SDR 值的对数正态分布不同，具有负偏度和正超峰度。通过包括对平面外分量的估计而制作的伪 3D SDR 显示出与对数正态分布的偏差减少。这种偏离可能归因于与喷嘴动量 AEI 缺失相关的强剪切层的消失。据作者所知，这项研究首次测量了衰变等温湍流射流中的 SDR。
The temporal development of the mixing field in a decaying jet (Re= 50,000) was quantified by measuring mole fraction and scalar dissipation rate (SDR) in a decaying, isothermal, turbulent gaseous jet. The 2D scalar field was measured by using planar laser induced fluorescence of acetone and, with appropriate image processing, this allowed estimation of the SDR using the two in-plane components within 16% error. The instantaneous and averaged distributions of the mole fraction are reported for downstream dimensionless distances up to 7 nozzle exit diameters and 35 exit flow timescales after end of injection. With advection of the last uniform exit concentration (UEC) profile core away from the nozzle exit, a region of weak concentration arises at the decaying jet's trailing edge. Estimates made in a Lagrangian frame of reference show that the trailing edge of the jet becomes leaner, after the end of injection (AEI), faster than in the steady state, confirming the existence of an ‘entrainment wave’. The normalised probability density functions of the 2D SDR at various stations and times AEI differ from a lognormal distribution at both low and high SDR values with negative skewness and positive excess kurtosis. A pseudo 3D SDR, made by including an estimate for the out of plane component, showed reduced departure from lognormal. The departure may be attributed to the disappearance of the strong shear layer associated with the absence of nozzle momentum AEI. To the authors’ knowledge, this study provides the first measurements of the SDR in a decaying, isothermal turbulent jet.
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