Total-Coverage Discrete Hole Wall Cooling

The present study investigates heat/mass transfer for flow through perforated plates for application to combustor wall and turbine blade film cooling. The experiments are conducted for hole length-to-diameter ratios 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 hole diameters, and for Reynolds numbers of 60 to 13,700. Local heat/mass 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 coefficients inside the hole surface vary significantly due to flow separation and reattachment. The transfer coefficient near the reattachment point is about four and half times that for a fully developed circular tube flow. The heat/mass transfer coefficient on the leeward surface has the same order as that on the windward surface because of a strong recirculation flow between neighboring jets from the array of holes. For flow through two in-line layers, the transfer coefficient affected by the gap spacing is approximately 100 percent higher on the windward surface of the second wall and is about 20 percent lower on the inside hole surface than that with a single layer. The transfer coefficient on the leeward surface is not affected by upstream flow conditions due probably to strong recirculation in the wake flow.