【摘要】 为了研究静态混合器内湍流速度的非稳态特性,在湍流状态下(Re=3972～11916)利用激光多普勒粒子分析仪下对直径为0.04m、长径比为1.25的SK型静态混合器的3维湍流瞬时流场进行测量。基于小波阈值消噪理论和分形理论,选用Sym小波基在不同消失矩N对瞬时速度时间序列进行多尺度分析。结果表明:静态混合器内瞬时速度信号呈现低维非周期长程自相似分形特性,Hurst指数在0.845～0.896之间波动;单个混合元件内,随着轴向位置的增加,Hurst数值先减小后增大,随着径向位移的增大Hurst数值呈先增大后减小的双峰分布;元件衔接处速度波动信号奇异性最强,N=8时速度波动信号分解误差最小。更多还原

【Abstract】 To characterize the instabilities of unsteady flow in Kenics Static Mixer(KSM) with 0.04 m in diameter and 1.25 in aspect ratio,the turbulent time series of instantaneous velocity fluctuation were measured by Laser Doppler Particle Analyzer in the turbulent region under the range of Re between 3972 and 11916.A method based on wavelet threshold de-noised transform and fractal theory was used to extract the large-scale turbulent signal with multip-scales resolution under different compact support Symlet wavelets.Results showed that the hurst exponents fluctuated between 0.845 and 0.896 which indicated that the instantaneous large-scale velocity fluctuation have persistence and self similarity fractal in lower phase space.The hurst exponents decreased firstly then increased as axial position increased,but increased firstly then decreased as radial position increased which have two peak value for the single mixing-element.Decomposition error was the minimum under Sym 8-order wavelet,and the velocity signal in the element-transition had the strongest singularity.更多还原