Evolution of the Vortical Structure of Flow in Ribbed Channels with Sinusoidal Flow Rate Variation

The study focused on the effect of three principal unsteady flow regimes on the processes of vortex inception and evolution in the near-wall layer of a channel with an array of ribs. A two-dimensional optical method was employed for measurements. The Strouhal number range considered in the study was 0.016 to 0.617. The normalized amplitude of forced pulsation of velocity ranged between 0.11 and 0.8. The data are given for the phases of forced pulsation of velocity with an increment of 0.25π. New hydrodynamic effects critical for heat and mass transfer enhancement were discovered, including a vortex circumnavigating the rib in upstream direction, reduction of the reattachment length to 1.1h in a phase of 0.5π and to average 3.4h over the period of forced pulsation, enhancement of mass transfer between the near-wall region and main flow over almost the entire surface of roughened wall.