Abstract
We experimentally study the combined effects of continuous ribs and rotations constructed in a square duct on the turbulent flows and flow separation. The ribs obstruct the channel by 10% of its height and are arranged in three different pitch-to-height ratios (P/e) of 10, 12, and 15. The Reynolds number (Re = ρU0D/μ) is fixed at 10 000, and the rotation number (Ro = ΩD/U0) varies from 0 to 0.52. A time-resolved particle image velocimetry system is applied to provide insights into the main flow and turbulence mechanism. Results show that rotation significantly changes main flow and turbulent characteristics. In particular, a main flow phenomenon has been found: on account of the secondary flow near the ribs, velocity profile deflects to the leading side under a low rotation number, and when Ro rises to 0.48 (critical value), velocity profile deflects to the trailing side. It gives an insight into main flow in a ribbed channel. Reattachment law has been investigated, which can optimize heat transfer by optimize rib arrangement. A proper orthogonal decomposition analysis is also considered to identify the spatial characteristics of the superimposed flow fields. Based on the experimental data, the existence of ribs with different P/e ratios and Coriolis forces play significant roles in rib-generated vortices as well as their turbulent activities.
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