Chaotic flow can be obtained in the viscoelastic fluid flow in the curved microchannel at very low Reynolds number. Influenced by the microstructures of viscoelastic fluid, the passive particles (scalar) transportation carried by the flow will be greatly enhanced. This paper presents a direct numerical simulation (DNS) for the chaotic viscoelastic flow and passive mixing in the curvilinear microchannel. The flow structures, mixing effect, passive scalar evolution with time are discussed. The simulations are conducted for a large range of viscoelasticity, which is parameterized by Weissenberg number (Wi). As Wi grows, the flow tends to a chaotic state, while the evolution of scalar gets strong and fast, showing excellent agreement with experiments. For the structures of scalar gradients in the flow field, they varies quickly in the form of isosurfaces with time, with “rolls” in the bulk changing into “threads” near the wall. That indicates the flow fields should be related to the micro deformation of viscoelastic molecules. The probability distribution function (pdf) analysis between micro-molecular deformation and flow field deformation shows that the main direction of molecular stretching is perpendicular to the main direction of flow field deformation. It implies they are weakly correlated, due to the confinement of channel wall.

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