Takahiro Miura;Koji Matsubara;Atsushi Sakurai
Direct numerical simulation was performed for air turbulent flows and heat transfer in a channel with square ribs attached to one wall. The spatially advancing cases and the fully advanced cases were both treated for the bulk Reynolds number of about 4,560. The rib height, H, was kept constant at 0.2 times the channel half-width, whereas the rib pitch was changed from Pi = 2H to 16 H. The heat transfer performance was evaluated using the ratio between the mean Nusselt number of the ribbed case and that of the smooth case requiring the same pumping power. This ratio was maximized at Pi/H = 9 for the fully advanced cases, but at Pi/H = 2 or 4 for the advancing cases. The mechanisms leading to this difference were discussed through turbulence statistics and their visualization. The thin thermal boundary layer in the advancing region was shown to increase heat transfer on the extended surface of Pi/H = 2 and 4, resulting the higher heat transfer performance than the case of sparse ribs. © 2012 The Japan Society of Mechanical Engineers.