Abstract: Fluid macro-instability reflects fluid axial energy and mass transfer behavior. To reveal the unsteady flow rule in a mixer-settler with rigid-flexible impeller, oil and water were used as working fluid, and the wavelet analysis and Matlab numerical calculation were adopted to analyze the power spectrum of pressure fluctuation signal in the mixing tank. The influences of rigid-flexible impeller on the frequency of macro-instability were studied, and CFD simulation was adopted to explore the flow field structure in the mixer-settler. Experiments showed that, while the agitation speed (N) of rigid-flexible impeller was lower than 250 r·min^-1, the relationship between macro-instability frequency (f_MI) and N was linear. When N was higher than 250 r·min^-1, much air was sucked into the liquid and f_MI disappeared, so the flow field became multi scale structure and resulted in serious emulsification, which was unfavorable for the operation of clarification. Compared with rigid impeller, the rigid-flexible one can enhance the macro-instability and improve the efficiency of fluid mixing and energy transfer. Computational simulation shows that, the rigid-flexible impeller could obviously increase the blade suction ability and axial movement of fluid, realizing efficient mixing and avoiding excessive stirring of the fluid, which is helpful to mixing and clarification.

Key words: computational fluid dynamics, two-phase flow, mixing, mixer-settler, macro-instability, rigid-flexible impeller

摘要： 流体宏观不稳定性可以反映流体轴向能量和质量的传递行为。为揭示刚柔组合搅拌桨（简称柔性桨）作用下混合澄清槽中油水液-液两相非稳态流动规律，采用频谱分析和小波分析组合法研究混合澄清槽内宏观不稳定性，并进行模拟验证。研究表明，柔性桨在转速低于250 r·min^-1时，流体宏观不稳定频率与转速呈线性关系，而转速超过250 r·min^-1，流体因界面卷吸行为吸入空气，宏观不稳定频率谱图呈现功率谱带，流场结构呈多尺度结构特征，流体宏观不稳定频率消失，液-液混合体系出现明显的乳化现象。与刚性桨相比柔性桨能增强宏观不稳定性，提高流体混合效率，强化能量传递行为。计算模拟发现，柔性桨能明显提高桨叶的抽吸能力，增强流体轴向运动的行为，避免流体过度搅拌，有利于流体澄清。

关键词: 计算流体力学, 两相流, 混合, 混合澄清槽, 宏观不稳定性, 刚柔组合搅拌桨