The three-dimensional flow field and heat transfer in a rib-roughened channel at large rotation numbers

The turbulent velocity field in a rotating rib-roughened channel is studied by means of incompressible Large Eddy Simulations (LES). The computations are validated against Particle Image Velocimetry (PIV) measurements performed in the symmetry plane of an experimental model of the same geometry. The present simulations consider the effect of the Coriolis force on a periodic section of low aspect ratio (AR = 0.9) and one rib-roughened wall. The Reynolds number based on the bulk velocity and the hydraulic diameter is fixed to 15,000, whereas the rotation number is set to 0, 0.31 and 0.77. Beyond the analysis of the Coriolis force influence on the shear layer stability, the present simulations allow to characterize the stream-wise secondary flows that redistribute the momentum through the cross-section at the different rotation numbers, the temperature distribution, and the resulting heat transfer on the wall. The flow structure is similar at rotation numbers equal to 0.31 and 0.77 when the channel rotates in the clockwise direction, with reduced turbulence and heat transfer on the ribbed wall, which acts as leading side. Only minor differences in the secondary flows and mean velocity profiles are observed due to the different magnitude of the Coriolis force. On the other hand, it has been observed that the secondary flow structure differs significantly when the rotation number is increased from 0.30 to 0.77 under counter-clockwise rotation. In particular, Taylor-Görtler vortices are observed together with the Coriolis-induced secondary flows at the maximum rotation rate, leading to a redistribution of the mean and turbulent velocity fields, as well as a significant change in the heat transfer distribution.