On the Underlying Drag-Reduction Mechanisms of Flow-Control Strategies in a Transitional Channel Flow: Temporal Approach

The underlying mechanisms of three different flow-control strategies on drag reduction in a channel flow are investigated by direct numerical simulations at friction Reynolds numbers ranging from 65 to 85. These include the addition long-chain polymers, incorporation slip surfaces, and application an external body force. While it has been believed that such methods lead skin-friction controlling near-wall structures, play still not as clear. In this study, temporal analysis is employed elucidate drag-reduction among these methods. based lifetime intermittent phases represented active hibernating minimal turbulent (Xi Graham, Phys Rev Lett 2010). At similar amount reduction, polymer show mechanism, while force method different. polymers surfaces cause happen more frequently, duration decreased. However, forces less frequently but prolong its achieve comparable reduction. A possible mechanism behind associated with unique roller-like vortical structures formed near wall. appear prevent interactions between inner outer regions which prolonged. It should motivate adaptive exploit distinct for robust control low numbers.