The simulation of stretch rates for the quantitative prediction and mapping of mixing within a channel flow

Abstract Numerical techniques for characterising the kinematic mixing rates and the distribution of mixing are presented. These techniques are evaluated for constant volumetric flow and oscillatory flow in a baffled channel. The mixing rate is obtained by two techniques, both of which are based on the stretch rate of infinitesimal lines, averaged over the flow volume. The mixing rate is independent of the numerical parameters and can relate to the rate of reduction of the scale of segregation. For constant volumetric flow, an instability leads to an unsteady flow and a rapid increase in the mixing rate. For oscillatory flow, the mixing rate was observed to be well distributed over the flow field for Reynolds numbers >80. The technique appears to be generally applicable to other flow geometries but requires knowledge of the velocity field.

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