The present study investigated the combined effects of the flow channel aspect ratio, the rib turbulator configuration, and the sharp 180-deg turn on the distributions of the local pressure drop in three-pass rectangular channels for a Reynolds number range of 15,000 to 60,000. The channel aspect ratios (the channel width-to-height ratios W/H; ribs on the channel width, W, side) were 1, 1/2, and 1/4. The rib height-to-hydraulic diameter ratios (E/D) were 0.063, 0.047, and 0.039; the rib pitch-to-height ratios (P/E) were 5, 7.5, 10, and 15; the rib angles of attack (α) were 90, 60, and 45 deg. The results showed that the rib turbulators dominated the pressure drops in the first pass of the three-pass channel. The pressure drops in the two-pass and the three-pass channels were caused by both the rib turbulators and the sharp 180-deg turns. The differences of the pressure drops caused by the different rib configurations (rib angle, spacing, and height) were significant in the first pass. The differences, however, were diluted by the sharp 180-deg turns in the two-pass and the three-pass channels, and by the smaller channel aspect ratio (W/H changed from 1 to 1/4). The friction factor correlations for the first pass, the first two-pass, and the three-pass were obtained to account for the rib configuration, the channel aspect ratio, and the Reynolds number. The correlations can be used in the design of the turbine airfoil cooling passages.

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