基于小波变换的鼓泡塔内气液两相湍流多尺度结构分析

Wavelet analysis of turbulent structure at superficial velocity in bubble column

在476mm的鼓泡塔内,以0.1～1m·s-1的高气速,利用Pavlov管测量塔内不同位置液相轴向速度,通过能谱分析发现,在空间区域上采用该方法测得的速度时间序列可分为含能尺度区和惯性子区,再借助7尺度Daubechie2小波分析的方法实现湍流量化指标如局部间歇性测度、间歇指数、尺度能量、涡旋尺寸等的评估.实验结果表明,高频和低频尺度下LIM峰分布表明湍流相干结构和大涡旋与小涡旋串级结构的存在.各小波尺度能量的比较说明,气速增大,高频和低频尺度的能量均增大,其中,含能尺度区间的能量占总能量的97%以上.不同尺度涡旋尺寸的计算证实了接近于塔内径最大涡旋的存在.进一步分析表明,塔壁处的涡旋尺寸约为塔中心处的2倍,含能尺度区间的涡旋尺寸为0.03～0.35m,气速对涡旋尺寸的影响可以忽略.湍流量化指标的分析有助于揭示湍流中的隐含结构以及高气速下鼓泡塔内湍流流动规律.

Liquid axial velocity was measured with Pavlov tube at a high superficial velocity （0. 1--1 m·s^-1） in a bubble column of 0. 476 m inner diameter. Power spectrum showed that velocity-time signal measured with Pavlov tube could be divided into energy range and inertial sub-range. Wavelet transform analysis was used for evaluating quantifiers of turbulence, such as local intermittency measure, intermittency index and flatness factor. The profile of fine scale and large sale LIM distribution showed the existence of coherent structure. Power distribution for various wavelet scales showed that fine scale and large scale power became larger with increasing gas velocity. The energy range contained over 97% of the total power, and the average eddy size in that region was between 0.03 m and 0.35 m. These quantifiers of turbulence were used for detecting the hidden structures and patterns in the velocity-time series, furthermore for understanding the rule of turbulence in the bubble column at high superficial velocity.