Topology and dynamics of streakline on the mixing boundary of two-dimensional chaotic flow induced by a rotationally reciprocating anchor impeller

Background: A rotationally reciprocating impeller separates the horizontal cross-section of the vessel into two mixing regions under a laminar flow regime. In this study, we investigated the separation mechanism from the dynamics of the streakline on the boundary Methods: The stretching behavior of the streakline on the universal boundary of active mixing regions was successfully visualized by injecting tracer fluid from a specific position Findings: The elongational rate of streakline proportionally increased with the increase in Reynolds number. Besides, the linear component of the elongation rate drastically changed at Re similar to 10 due to the bending of the boundary. Compared with other chaotic mixing flows, we proved that tracer particles are enclosed in turnstile lobes at the hyperbolic fixed point at the wall, transported on the boundary, namely separatrix, to the mixing shaft being another hyperbolic fixed point, and then distributed evenly into both mixing regions. It was concluded that the boundary becomes wavy at Re > 10, which increases the area of turnstile lobes to enhance fluid transportation between two mixing regions (C) 2022 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Automated summary

This study investigates the separation mechanism of a rotationally reciprocating impeller through visualizing the stretching behavior of streaklines. The elongational rate of streaklines is found to increase proportionally with the increase in Reynolds number, and the bending of the boundary significantly affects the linear component of the elongation rate. Compared with other chaotic mixing flows, tracer particles are enclosed in turnstile lobes at the hyperbolic fixed point at the wall, transported on the boundary (separatrix), and then evenly distributed into both mixing regions. It is concluded that the waviness of the boundary enhances fluid transportation between the two mixing regions when the Reynolds number is greater than 10.