Effect of Coriolis forces in a rotating channel with dimples and protrusions

Large-eddy simulations are used to investigate the effect of Coriolis forces and dimple depth on heat transfer and friction in a channel with dimples and protrusions on either side. Two geometries with two different dimple-protrusion depths, delta = 0.2 and 0.3 of channel height are investigated over a wide range of rotation numbers, Ro(b) = -0.77 to 1.10 based on mean velocity and channel height. It is found that the dimple side of the channel is much more sensitive to destabilizing rotational Coriolis forces than the protrusion side of the channel, although both dimples and protrusions react to the stabilizing effects of Coriolis forces on the leading side. The dimpled surface on the trailing side experiences a large increase in heat transfer coefficient from an augmentation ratio of 1.9 for stationary flow to 3.5 at Ro(b) = 0.77 for delta = 0.2, and from 2.3 to a maximum of 3.8 for delta = 0.3. Placing protrusion on the trailing side, however, only increases the augmentation ratio to between 3.25 and 3.7 from the stationary values of 3.0 and 3.4 for delta = 0.2 and 0.3, respectively. The dimpled leading side experiences a large drop in heat transfer to between augmentation ratios of 1.1 and 1.4 for the two dimple depths. The protrusion surface on the leading side also experiences a large drop in augmentation from 3.0 for a stationary channel to 1.3 at Ro(b) = 0.77 for delta = 0.2 and from 3.4 to 1.8 at Ro(b) = 1.1 for delta = 0.3. The results lead to the conclusion that for low rotation numbers |Ro(b)| < 0.2, placing protrusions on the trailing side is advantageous, whereas for |Ro(b)| > 0.2, dimples on the trailing side of the duct give better overall performance. Between the two depths, the deeper dimple/protrusion (delta = 0.3) gives higher heat transfer augmentation at the price of more frictional losses ranging from 6 to 10 versus 3 to 5 for depth delta = 0.2. (C) 2009 Elsevier Inc. All rights reserved.