Abstract
The linear and non-linear growth of instabilities in a two dimensional parallel three jet flow configuration is carried out using DNS. A method is presented that enables the study of growth of instability modes using a combination of LSA and DNS. The linear growth of spatial and temporal LSA modes for a single shear layer is verified using DNS. Then DNS is used to study the transition from linear growth to non-linear instabilities. In test, the growth rate of temporal modes found using DNS matches with growth rate predicted by LSA for viscous and inviscid flows. DNS of a non-parallel flow with a spatially growing viscous LSA mode is found to create absolute instability and match between DNS and LSA is not possible. In a temporal analysis, it is found for a multiple shear layer case it is found that the growth of the temporal mode increases with increasing the strength of the additional shear layer for both inviscid and viscous flows. Longer DNS runs show that presence of a stronger shear layer enhances vortex shedding and vortex pairing mechanism of a shear layer. This enhanced mixing in the non-linear region is to be linked with the growth of perturbation in the linear region.
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