Heat Transfer and Film Cooling in an Aggressive Turbine Center Frame

This article investigates the heat transfer coefficient and the film cooling effectiveness in a turbine center frame (TCF). The TCF is a duct connecting the high-pressure turbine (HPT) to the low-pressure turbine (LPT) and is equipped with nonturning airfoils (struts). The TCF is operated in a product-representative 1.5-stage test turbine setup working under Mach number similarity. Upstream of the TCF, an unshrouded HPT is operated with four individually adjustable purge flow injections through the forward and aft cavities on the hub and tip of the rotor. The heat transfer coefficient and the purge film cooling effectiveness are measured on the hub and the nonturning struts of the aerodynamically aggressive TCF using infrared thermography and tailor-made heating foils. To further extend the film cooling investigation, the seed gas concentration technique, in conjunction with the heat-mass transfer analogy, is used as a second film cooling measurement technique. Seeding the HPT cavities with different foreign gases reveals every individual purge flow's contribution to the global film cooling effectiveness in the TCF. In addition, the seed gas technique extends the investigated area for film cooling to the optically inaccessible shroud of the TCF. The heat transfer in the TCF was found to be dominated by secondary flow features of the upstream HPT. Longitudinal streaks of alternating high and low heat transfer were found on the hub connected to the number and the position of the upstream HPT vanes. A similar pattern was found in the film cooling effectiveness, where the film cooling streaks were situated between the high heat transfer streaks. The film cooling coverage on the shroud was found to be even, symmetric, and superior to the hub cooling performance, with around 10% less usage of purge mass flow.