TOTAL-COVERAGE DISCRETE HOLE WALL COOLING

The present study investigates heat/mass transfer for flow through per forated plates for application to combustor wall and turbine blade fil m cooling. The experiments are conducted for hole length-to-diameter r atios of 0.68 to 1.5, for hole pitch-to-diameter ratios of 1.5 and 3.0 , for gap distance between two parallel perforated plates of 0 to 3 ho le diameters, and for Reynolds numbers of 60 to 13,700. Local heat/mas s transfer coefficients near and inside the cooling holes are obtained using a naphthalene sublimation technique. Detailed knowledge of the local transfer coefficients is essential to analyze thermal stress in turbine components. The results indicate that the heat/mass transfer c oefficients inside the hole surface vary significantly due to flow sep aration and reattachment. The transfer coefficient near the reattachme nt point is about four and half times that for a fully developed circu lar tube flow. The heat/mass transfer coefficient on the leeward surfa ce has the same order as that on the windward surface because of a str ong recirculation flow between neighboring jets from the array of hole s. For flow through two in-line layers, the transfer coefficient affec ted by the gap spacing is approximately 100 percent higher on the wind ward surface of the second wall and is about 20 percent lower on the i nside hole surface than that with a single layer. The transfer coeffic ient on the leeward surface is not affected by upstream flow condition s due probably to strong recirculation in the wake flow.