旋流静态混合器内瞬态速度时间序列多尺度符号化分析

Multi-scale Symbolic Analysis of Instantaneous Velocity Time Series in the Static Mixer with Twisted-leaves

利用激光多普勒粒子分析仪对长径比为1.25的旋流静态混合器内瞬态流场进行测量.基于经验模态分解(EMD)方法将测得SK型静态混合器速度信号进行多尺度分解,并将分解的各阶固有模态函数IMF进行符号化,采用修正的Shannon熵(Hs)评价各尺度下的微观动力学特征.通过对静态混合器内不同尺度下瞬态速度波动信号的Hs分析,发现轴向速度和径向速度拥有不同的动力学特征:当流体微团波动频率低于7.81Hz时,轴向速度波动稳定性高于径向速度.随着漩涡尺度的减小,静态混合系统的随机性程度增加.轴向速度高频分量波动随机性高于径向速度高频分量,轴向Hs值随速度波动尺度增加的衰减速率高于径向Hs.Hilbert谱分析表明速度脉动在0.489Hz处取得能量峰值,径向速度的能量峰值且达到轴向速度39.57%.

The instantaneous flow field in static mixer with twisted-leaves with 1.25 in the aspect ratio was measured used the Laser Doppler particle analyzer.The velocity fluctuation signals were multi-scale decomposed by use of Empirical Mode Decomposition（EMD）method.Each scale intrinsic mode function（IMF）and corresponding symbolic time series was obtained.The modified Shannon entropy（Hs）was used to evaluate the microcosmic kinetics characteristics.By analysis the profiles of Hs at different scales,it was found that the axial and radial velocity had different dynamic characteristics.The axial velocity had higher determinacy motion feature than radial velocity when pulsation frequency of fluid micelle was below 7.81Hz.The stochastic degree of static mixing system became stronger with the pulsation frequency increase.The axial velocity showed stronger randomness characteristic than radial velocity at high-frequency sections,and the axial attenuation rate between Hs and pulsation frequency is higher than radial component.The peak values of fluctuant energy were acquired at f=0.489Hz.The Hilbert spectrum revealed that the energy ratio between the maximum of radial velocity and axial velocity achieve 39.57%.