THE SIMULATION OF STRETCH RATES FOR THE QUANTITATIVE PREDICTION AND MAPPING OF MIXING WITHIN A CHANNEL FLOW

Numerical techniques for characterising the kinematic mixing rates and the distribution of mixing are presented. These techniques are evalua ted for constant volumetric flow and oscillatory Bow in a baffled chan nel. The mixing rate is obtained by two techniques, both of which are based on the stretch rate of infinitesimal lines, averaged over the fl ow volume. The mixing rate is independent of the numerical parameters and can relate to the rate of reduction of the scale of segregation. F or constant volumetric flow, an instability leads to an unsteady Bow a nd a rapid increase in the mixing rate. For oscillatory flow, the mixi ng rate was observed to be well distributed over the Row field for Rey nolds numbers > 80. The technique appears to be generally applicable t o other Bow geometries but requires knowledge of the velocity field.