Effect of centerline distance on mixing of a Non-Newtonian fluid in a cavity with asymmetric rotors

Mixing of highly viscous fluids in a cavity with internal moving parts is a common scenario found in many engineering applications. It provides a challenge for numerical simulations. In this paper, asymmetric rotors were designed to enhance mixing, and the effect of different centerline distances on mixing was investigated numerically. The novel rotors co-rotate at a speed ratio of 2 and hence have different geometries to meet the requirement of self-cleaning. The finite element method was used to solve the time-dependent flow, in which the mesh superposition technique was used to include the internal moving parts in the fixed meshes of the flow domain. A non-Newtonian fluid obeying the Carreau–Yasuda constitutive model was used. A standard fourth-order Runge–Kutta scheme was successfully developed to perform the particle tracking calculations. Distributive mixing was examined through the flow patterns and spatial positions of the tracked particles. The centerline distance was the key factor for controlling the gap between the rotors that influence mixing and energy consumption. Different mixing subzones alternated in sequence. On the one hand, this gap introduced a bifurcation in the intermeshing zone. On the other hand, stretching, folding, and reorientations, as well as cutting and dividing actions, were encountered in the sequence. This procedure was similar to a Baker’s transformation. By contrast, for a Newtonian fluid, mixing became worse and consumed slightly more energy.