Rib spacing effect on heat transfer in rotating two-pass ribbed channel (AR = 1:2)

Rib turbulators are commonly used to enhance the heat transfer within internal cooling passages of advanced gas turbine blades. Many factors affect the thermal performance of a cooling channel with ribs. This study experimentally investigates the effect of rib spacing on the heat transfer enhancement, pressure penalty, and thus the overall thermal performance in both rotating and nonrotating rectangular, cooling channels. In the 1:2 rectangular channels, 45 deg angled ribs are placed on the leading and trailing surfaces. The pitch of the ribs varies, so rib pitch-to-height (P/e) ratios of 10,7.5, 5, and 3 are considered. Square ribs with a 1.59 mm × 1.59 mm cross section are used for all rib spacing, so the height-to-hydraulic diameter (e/D _h) ratio remains constant at 0.094. With a constant rotational speed of 550 rpm and the Reynolds number ranging from 5000 to 40,000, the rotation number in turn varies from 0.2 to 0.02. Because the skewed turbulators induce secondary flow along the length of the rib, the very close rib spacing of P/e = 3 has the best thermal performance in both rotating and nonrotating channels. This close spacing yields the greatest heat transfer enhancement, whereas the P/e = 5 spacing has the greatest pressure penalty. In addition, the effect of rotation is more pronounced in the channel with the rib spacing of 3. As more ribs are added, the channel is approaching a smooth channel, and the strength of the rotation induced vortices increases.