Film Cooling and Heat Transfer on Two Cutback Trailing Edge Models With Internal Perforated Blockages

Abstract

Experiments to study heat transfer and film cooling on the cutback trailing edge of a turbine blade with slot ejection were performed. Heat transfer from two rows of perforated blockage inserts for lateral impingement on the coolant channel walls prior to coolant ejection into the freestream was also investigated. The internal test geometry is similar to the crossover impingement hole design used in modern gas turbine blades for trailing edge cooling. A liquid crystal technique based on hue value detection was used to measure the heat transfer coefficient on a trailing edge film-cooling model with slot ejection and an internal model with perforated blockage inserts. It was also used to determine the film effectiveness on the cutback trailing edge. For the internal model with the perforated blockage inserts, Reynolds numbers based on the hydraulic diameter of the slot and exit velocity were 5000, 10,000, 20,000, and 30,000 and corresponding coolant-to-freestream velocity ratios ranged from 0.26 to 1.83 for the external model with slot ejection, respectively. The experiments were performed for two different designs, 1 and 2, with Design 1 incorporating two different configurations with a staggered/inline slot exit arrangement and Design 2 with a staggered slot exit arrangement. Both designs utilized a 90deg flow turn into the blockage inserts as an entrance to the test section to simulate a realistic blade passage design. Results show that the internal design geometry of the trailing edge and Reynolds numbers can affect heat transfer in an internal model with perforated blockage inserts. Design 2 with a wider entrance channel and a sloped land near the ejection slots provided low heat transfer coefficients in the internal as well as external model but gave higher film-cooling effectiveness from slot ejection.