a1 Graduate School of Engineering, Hokkaido University, N13W8, Sapporo 060-8628, Japan
a2 Research Institute for Electronic Science, Hokkaido University, N20W10, Sapporo 001-0020, Japan
We study ‘surface switching’ quantitatively in flows driven by the constant rotation of the endwall of an open cylindrical vessel reported by Suzuki, Iima & Hayase (Phys. Fluids, vol. 18, 2006, p. 101701): the deformed free surface switches between axisymmetric and non-axisymmetric shapes accompanied by irregular vertical oscillation. Detailed simultaneous measurements showed that the magnitude of the velocity fluctuations (turbulent intensity) temporally varies greatly and are strongly correlated with the surface height, suggesting that dynamic switching between laminar and turbulent states is accompanied by vessel-scale surface shape changes. The study also identified clear hysteresis in the turbulent intensity arising from changes in the Reynolds number; the bifurcation diagram consists of two overlapping branches representing a high-intensity (turbulent) state and a low-intensity (laminar) state. Based on the results, a switching mechanism is suggested.
(Received March 26 2009)
(Revised June 25 2009)
(Accepted June 26 2009)