Interaction of secondary flow with developing, turbulent boundary layers in a rotating duct

Investigations of the interaction of secondary flow with developing, turbulent boundary layer in a rotating square-section straight channel have been done in a new rotating facility with normal hot wire anemometry. The measurements are performed with Re=18391 and Ro=0, 0.116, 0.232, respectively, characterized by the channel hydraulic diameter of 80 mm and the bulk mean velocity. Measurements at five stations distributed in the streamwise direction have been done to study the turbulent boundary layer streamwise development. The mean velocity profiles in both ordinary and semi-logarithm coordinates and skin shear velocities at these test stations are obtained. On the leading side, the skin shear velocity firstly decreases, and then increases in the streamwise direction. This phenomenon is analogous to the critical rotation number phenomenon revealed in previous work with heat transfer. Based on this analogy, a new possible explanation of the critical rotation number phenomenon is given here. The semi-logarithm mean velocity profile is found to not obey the traditional log-law linear rotation correction. This suggested the need of a secondary flow strength correction of the log law with system rotation.