射流卷吸边界层内相干结构的实验研究

doi:10.11949/0438-1157.20190048

摘要/Abstract

摘要：

在轴对称水射流实验台上，采用单帧长曝光图像法，测量了出口Reynolds数在1849~2509范围内的卷吸边界层内流场结构。发现在流向距离L=2D~3.5D，径向距离H=D~1.25D的区域内，流场中吞噬作用和侵蚀作用两种卷吸模式交替出现。分析得到，当Re>1915时，吞噬作用所占的比例随着Re的增大而增大，当Re>2311之后，Reynolds数对该结构发生概率的影响降低；通过快速傅里叶变换得到该相干结构发生的频率在10～19Hz之间；吞噬作用发生的同时在流场中观测到一些特殊涡结构。同时采用运动单帧长曝光图像法对射流流场进行拉格朗日法观测，发现射流流场中的涡结构一般存在于湍流与非湍流界面附近。

关键词: 单帧长曝光, 运动单帧长曝光, 卷吸边界层, 射流, 湍流与非湍流界面, 涡结构

Abstract:

On the axis-symmetric water jet test bench, the flow field structure in the entrainment boundary layer with the Reynolds number in the range of 1849－2509 was measured by the single-frame long exposure image method. It is found that engulfing and nibbling entrainment model occur intermittently with time, in the region of L=2D－3.5D streamwise and H=D－1.25D radial direction. It concludes from analyzing that the occurrence probability of engulfing increases with Reynolds number when Re>1915, the influence of Reynolds number on the occurrence probability of this structure decreases when Re>2311.The occurrence frequency of this coherent structure obtained by fast Fourier transform is between 10 Hz and 19 Hz. Special vortex structures were observed in the flow field during the occurrence of engulfing. The jet flow field are measured using moving single frame long exposure image method in Lagrangian coordinate system, and it is found that the vortex structure generally existed near the interface of turbulent regions and non-turbulent regions.

Key words: single frame long exposure, move single frame long exposure, entrainment layers, jet, turbulent and non-turbulent interface, vortex structures

中图分类号:

TQ 028.8

周雷, 周骛, 郭延昂, 蔡小舒. 射流卷吸边界层内相干结构的实验研究[J]. 化工学报, 2019, 70(7): 2520-2527.

Lei ZHOU, Wu ZHOU, Yan ang GUO, Xiaoshu CAI. Experimental studies on coherent structures in jet entrainment boundary layers[J]. CIESC Journal, 2019, 70(7): 2520-2527.

图/表 11

图1 典型颗粒运动轨迹的物理模型

Fig.1 Physical model of typical particle trajectories

图2 单帧长曝光图像法原理

Fig.2 Principle of SFLE image method

图3 淹没水射流实验系统

Fig.3 Submerged water jet apparatus

图4 射流卷吸边界层附近流场随时间的变化 (Re=2047)

Fig.4 Flow field near entrainment boundary layers of jet changing with time (Re=2047)

图5 特殊迹线结构(图中射流从图右流向图左，Re=2179)

Fig.5 Peculiar trajectory structure (Re=2179)

表1 不同Re下吞噬作用帧数与总帧数的比值

Table 1 Ratio of engulfing frames to total number of frames at different Reynolds numbers

Re	Engulfing	Total	Proportion/%
1981	201	1357	14.8
2047	232	1353	17.1
2113	287	1414	20.3
2179	354	1403	25.3
2245	387	1409	27.5
2311	409	1400	29.2
2377	417	1383	30.2

图6 吞噬作用发生的帧数占总帧数的比例随Reynolds数的变化

Fig.6 Ratio of engulfing frames to total frame number varied with Reynolds number

图7 吞噬作用发生的间隔帧数随Reynolds数的变化

Fig.7 Interval of engulfing varied with Reynolds number

图8 经过FFT得到不同Reynolds数下相干结构发生的频率

Fig.8 Frequencies of engulfing obtained by FFT at different Reynolds numbers

图9 运动单帧长曝光图像法获得的射流流场（Re=1909）

Fig.9 Jet flow field obtained by MSFLE image method (Re=1909)

图10 运动单帧长曝光观测到流场中涡结构的演变情况（Re=1909）

Fig.10 Evolution of vortex structure obtained by MSFLE image method in flow field (Re=1909)

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