Effect of Rib Turbulators in the First Pass on Heat Transfer Distributions in a Two-Pass Channel Connected by Two Rows of Holes

Abstract

This paper is a continued study of new internal channel cooling designs for modern gas turbine blades. In previous studies, the enhanced cooling in the second pass of a serpentine channel was achieved by a combination of impingement and crossflow-induced swirl. A holed or slotted divider wall replaced the 180° U-turn connecting the two legs of the serpentine channel. Flow from one coolant passage to the adjoining coolant passage was achieved through a series of straight and angled holes and a two-dimensional slot placed along the dividing wall. In this study, the focus is to enhance the heat transfer in the first pass of the two-pass channel using traditional rib turbulators. The effect of ribs in the first pass on the overall second pass heat transfer enhancement is compared to channels with no rib turbulators. Heat transfer distributions are compared for channels with and without ribs for three-channel flow Reynolds numbers ranging between 1.0×104 − 5.0×104. Results show that the presence of the ribs in the first pass reduces the heat transfer coefficients slightly in the second pass compared to the no-ribs channels. However, the first pass heat transfer is significantly enhanced over the case without ribs. In effect, the overall heat transfer enhancement for the combined two passes is significantly enhanced. Three different rib configurations, 90° ribs, 60° angled forward facing towards divider wall, and 60° angled backward facing away from divider wall, are studied for all Reynolds numbers and divider wall geometries. The presence of ribs in the first pass does not only decrease the enhanced heat transfer in the second pass but also provides higher heat transfer enhancement in the first pass resulting in an increase in overall heat transfer enhancement for the entire two-pass channel.