Detailed heat transfer distributions in two-pass smooth and turbulated square channels with bleed holes
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abstract
Modern gas turbine blades have internal serpentine passage for providing effective cooling. Rib turbulators are added periodically on the cooling passage surface to enhance heat transfer. Some of the cooling air is ejected out through bleed (or film) holes for external blade film cooling. The presence of periodic rib turbulators and bleed holes creates strong axial and spanwise variations in the heat transfer distributions on the passage surface. Detailed heat transfer coefficient distributions are presented in this study for a two-pass square channel with a 180 turn. One wall of the channel has periodically placed bleed holes. Four different configurations of 90 parallel, 60 parallel, 60 V ribs, and 60 inverted V ribs are studied in conjunction with the effect of bleed holes on the same wall. The surface is coated with a thin layer of thermochromic liquid crystals and a transient test is run to obtain the detailed heat transfer distributions. The 60 parallel, 60 V, and 60 inverted ribbed channels produce similar levels of heat transfer enhancement in the first pass. However, the 60 inverted V ribbed channel produces higher enhancement in the second pass. Regional averaged heat transfer results indicate that a test surface with bleed holes provides similar heat transfer enhancement as that for a test surface without bleed holes although 20-25% of the inlet mass flow exits through the bleed holes.
