Swirl-Enhanced Internal Cooling of Turbine Blades: Part 1—Radial Flow Entry

Abstract

Heat transfer results for a given slot shaped channel with a 3:1 aspect ratio and jets issuing from side walls are presented. Two different jet configurations are used as a means to enhance turbulence in the main flow stream. The Reynolds numbers investigated range from 10,000 to 50,000 and are based on the mean velocity of the fluid at the channel inlet for the slot shaped channel without enhancement, or when swirl-jets are used, the equivalent mass flow rates at the exit of the main channel. Blowing Ratios, defined as the mean side jet velocity verses the mean main channel velocity, ranged from 8.6 to 30.2. This heat transfer enhancement strategy has proven to be effective in round channels. A transient technique combined with Duhamel’s superposition theorem was used to obtain the heat transfer coefficient distributions. Narrow-band liquid crystals were used to map the transient surface temperatures and were combined with thermocouples that measured the center-line air temperatures along the flow path in the main channel. The results of the passage with jet enhancements were compared to the smooth slot channel, without any type of heat transfer enhancements. The tests results reported in this paper show mean heat transfer enhancement values (Nu/Nuo smooth) greater than 4.2 and low normalized friction factors. Thermal performance factors (OTP) ranged from 1.55–3.69 for the various configurations studied. These results show significant improvements over other types of heat transfer enhancement methods currently used in the mid-span section of turbine blades.