Numerical investigation on mixing efficiency and exponential fluid stretching in chaotic mixing

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