The Design, Fabrication, and Validation of a Film Cooled Rotating Turbine Cascade with an Actively Cooled Shroud in a Closed Loop Wind Tunnel
Master of Science in Mechanical Engineering (MSME)
To test shroud and blade cooling effectiveness, a closed loop, heated wind tunnel housing a film cooled rotating turbine cascade with prescribed blade and vane geometry surrounded by a fully cooled shroud with a leading edge gap were designed and assembled on Louisiana State University’s campus. Heat transfer coefficients and film cooling effectiveness results were computed using a 1-D semi-infinite solid conduction analysis of material temperatures obtained with liquid crystal thermography. Proper analysis required a step change in air temperature; so a bypass loop provided mainstream air heating while maintaining the shroud and blades at ambient temperature. Also, analysis required hollow tip film cooled turbine blades constructed of low thermal conductivity material, resulting in fabrication by 3-D plastic printing. An analytical stress model and finite element analysis validated plastic blade structural base design. Static-structural and dynamic fatigue loading analyses determined rotor shaft size. Heat transfer and pressure loss calculations verified the system’s required blade and shroud cooling characteristics. Finally, velocity vector measurements at the nozzle guide vane leading edge and recorded pressures in a nozzle guide vane passageway upstream of the turbine cascade location validated incoming freestream flow properties for the design condition at which heat transfer measurements were recorded. A total pressure loss analysis for varying rotor speed and blowing ratio was conducted with the development of total pressure contours downstream of the exit guide vanes to understand losses in the nozzle-rotor passage. Loss structures were found at the tip and root of the exit guide vane, attributed to the shed vortex and tip leakage vortex developed from the rotor blade. Total pressure loss decreased as blowing ratio increased due to energy added to the mainstream flow through the film cooling air. Rotor speed was varied from 55 to 655 RPM. Total pressure losses were lowest at 55 RPM, increased with increasing rotor speed past the 355 RPM design speed, and decreased as rotor speed approached 655 RPM. These results could be attributed to the introduction or extraction of shaft work in the rotating system along with aerodynamic losses associated with changes from the incidence angle design.
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Drewes, Christopher Michael, "The Design, Fabrication, and Validation of a Film Cooled Rotating Turbine Cascade with an Actively Cooled Shroud in a Closed Loop Wind Tunnel" (2016). LSU Master's Theses. 2030.