Effects of Pulsing on Film Cooling of Gas Turbine Airfoils

Abstract

_________________________________________(signature) ____________________________ (date) REPORT DOCUMENTATION PAGE Form Approved OMB No. 074-0188Public reporting burden for this collection of information is estimated to average 1 hour per response, including g the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. ABSTRACT:The objective of this project was to determine the effects of pulsed film cooling on turbine blades. High combustor temperatures, resulting in elevated turbine inlet temperatures, produce high engine efficiency. At current operating temperatures, the turbine inlet temperature is above the melting point of the turbine blades. Thus cooling the blades in the first stages after the combustor is essential. Current methods for film cooling utilize a continuous stream of bleed air from the compressor. This air is routed into a cavity inside each blade and bled out of holes onto the blade surface, creating a film of cool air. Pulsed film cooling may reduce the amount of bleed air used, thus increasing the efficiency of the engine by allowing more air to flow through the combustor, while providing equivalent protection for the blades. In this study, a section of a turbine blade was modeled using a plate with a row of five film cooling holes. Coolant air was pulsed via solenoid valves from a plenum, while a wind tunnel provided a mainstream flow. Temperature and velocity fields were measured over the blade surface with varying blowing rates of the coolant and frequencies of pulsing. The film cooling effectiveness, a measure of how well the coolant protects the blade surface, was calculated based on the measured temperatures. The results were compared to baseline cases with continuous blowing and no blowing. The overall best case was continuous film cooling with the jet velocity one fourth of the mainstream velocity. However, results showed that pulsed film cooling has the potential to provide an equivalent or greater film cooling effectiveness for higher jet velocities. The case of pulsed jets with a jet velocity equal to the mainstream velocity, pulsing frequency of 20 Hertz, and 75% duty cycle showed an increased film cooling effectiveness and decreased heat transfer compared to the continuous blowing case. This study suggests that pulsed film cooling has the potential to adequately protect gas turbine blades with additional research, ultimately allowing for an increased efficiency in a gas turbine engine. 1 ABSTRACT: The objective of this project was to determine the effects of pulsed film cooling on turbine blades. High combustor temperatures, resulting in elevated turbine inlet temperatures, produce high engine efficiency. At current operating temperatures, the turbine inlet temperature is above the melting point of the turbine blades. Thus cooling the blades in the first stages after the combustor is essential. Current methods for film cooling utilize a continuous stream of bleed ...