A NUMERICAL EULERIAN APPROACH TO MIXING BY CHAOTIC ADVECTION

Results of numerical simulation of the advection-diffusion equation at large Peclet number are reported, describing the mixing of a scalar f ield under the action of diffusion and of a class of steady, bounded, three-dimensional flows, which can have chaotic streamlines. The time evolution of the variance of scalar field is calculated for different flow parameters and shown to undergo modulated exponential decay, with a decay rate which is a maximum for certain values of the flow parame ters, corresponding to cases in which the streamlines are chaotic ever ywhere. If such global chaos is present, the decay rate tends to oscil late, whereas the presence of regular regions produces a more constant decay rate. Significantly different decay rates are obtained dependin g on the detailed properties of the chaotic streamlines. The relations hip between the decay rate and the characteristic Lyapunov exponents o f the flow is also investigated. (C) 1995 American Institute of Physic s.