关键词: Chaos, Pseudoplastic fluids, Largest Lyapunov exponent (LLE), Kolmogorov entropy (K entropy), Particle image velocimetry (PIV), 6PBT impeller

Abstract: Xanthan gum solutions with different mass concentrations were used to study the chaotic characteristics induced by the impeller of perturbed six-bent-blade turbine (6PBT) in a stirred vessel. Based on the velocity time series obtained by the experiment of particle image velocimetry (PIV), with the software MATLAB (R2016a), the distributions of the largest Lyapunov exponent (LLE) and Kolmogorov entropy (K entropy) of the system, as two important parameters for characterizing the chaotic degree, were investigated respectively. Results showed that both of the LLE and K entropy increased with the increasing speed at the beginning. As the speed was up to 200 r·min^-1, the two parameters reached the maximal values meanwhile, corresponding to 0.535 and 0.834, respectively, which indicated that the chaotic degree of the flow field was up to the highest level. When the speed was increased further, both of the LLE and K entropy decreased on the contrary, which meant that the chaotic degree was decreasing. It was also observed that the chaotic characteristics of flow field were hardly affected by the fluid rheology and the detecting positions. The research results will enhance the understanding of the chaotic mixing mechanism and provide a theoretical reference for optimizing impeller structure.

Key words: Chaos, Pseudoplastic fluids, Largest Lyapunov exponent (LLE), Kolmogorov entropy (K entropy), Particle image velocimetry (PIV), 6PBT impeller