Investigation of Heat Transfer Enhancement and Pressure Characteristics of Zig-Zag Channels

Described in this paper is a study combining experiment and CFD simulation to explore the heat transfer characteristics of an internal cooling passage with different turning angles ranging from 70, 90 and 110 degrees. When adjacent passages are connected by a turn in a periodic fashion, the channel exhibits a “zig-zag” pattern, and hence the name. The test channel has a cross-section of 63.5mm by 25.4mm, corresponding to the aspect ratio of 2.5:1. This specific design with several turns will generate additional secondary vortices while providing longer flow path that allows coolant to remove a greater heat load before being discharged downstream. The computational study employs a commercially available CFD code, ANSYS CFX. As a significant finding, the numerical simulation suggested that the case with 110 degree turns has the best heat transfer performance. An experimental study thus is followed to investigate the detailed surface heat transfer distribution on the 110 degree case using the transient liquid crystal technique. The overall heat transfer coefficient characteristics except near the turning region are found to be comparable between the experimental and numerical simulation. Pressure loss in these test channels is several folds higher than that of straight smooth test channel due to the presence of turns; but is it significant lower than the limiting case with a 180-degree turn. The case with 70 degree turns has the highest pressure loss, while the case with 110 degree turns has the lowest pressure loss. Internal channels of zig-zag configurations might be a viable design for internal cooling of an airfoil mainbody or trailing edge while serving the purpose of bridging structures between the pressure and suction sides.