Heat transfer and flow characteristics of U-shaped cooling channels with novel wavy ribs under stationary and rotating conditions

Wavy rib is a kind of novel turbulator that can effectively improve the ribbed wall heat transfer of cooling channel and produce acceptable friction loss. Meanwhile, it has the advantage of simple structure. In this paper, the effects of wavy ribs on the heat transfer distributions of ribbed walls, side walls, and top wall are numerically studied in stationary and rotating U-shaped channels. The flow characteristics of cooling air are also analyzed. Taking the 45° V-shaped ribs as the reference scheme, the high-performance wavy ribs that have better heat transfer performance on ribbed wall and induce the same friction loss are selected. The channel aspect ratio is 1, with the height of 12.7 mm. The investigated Reynolds number is 25,000, and the rotation number is 0, 0.2, 0.3 and 0.4. Rib height (e-3e), rib round radius (0-5 mm), and rib angle (20-55°) are the three major geometrical parameters of wavy rib. The results show that, the diversion effect of wavy ribs on cooling air is the reason of friction loss suppression. On the one hand, the wavy ribs confine the fluid disturbance on side walls, leading to the heat transfer reduction. On the other hand, the impingement of cooling air on the channel top wall is strengthened, which improves the wall heat transfer. In stationary and rotating conditions, the high-performance wavy ribs increase the heat flux on heated surface corresponding to the ribbed wall by 5-21% and 4-24% respectively, and weaken the effect of Coriolis force on the heat transfer of the first pass. With the increase of rotation number, the friction penalty and heat transfer of leading side ribbed wall decrease, while the heat transfer of trailing side ribbed wall slightly increases, showing that those high-performance wavy ribs have a good versatility at multiple rotation numbers.