Abstract: The stretching and folding of fluid element during chaotic mixing field is studied using
numerical method. The chaotic mixing process is caused by periodic secondary flow in a
twisted curved pipe. Using the nonlinear discrete velocity field as the dynamical system,
the present study connects the fluid particle’s stretching along its trajectory in one
period to a linearized time-varying variational equation. After numerical approximation of
the variational equation, fluid stretching is calculated on the whole cross section. The
stretching distribution shows an exponential fluid stretching and folding, which indicates
an excellent mixing performance.

Key words: chaotic mixing, secondary flow, numerical approximation

摘要： The stretching and folding of fluid element during chaotic mixing field is studied using
numerical method. The chaotic mixing process is caused by periodic secondary flow in a
twisted curved pipe. Using the nonlinear discrete velocity field as the dynamical system,
the present study connects the fluid particle’s stretching along its trajectory in one
period to a linearized time-varying variational equation. After numerical approximation of
the variational equation, fluid stretching is calculated on the whole cross section. The
stretching distribution shows an exponential fluid stretching and folding, which indicates
an excellent mixing performance.

关键词: chaotic mixing;secondary flow;numerical approximation