In-Situ Calibration of Infrared Film Cooling Measurements with the Seed Gas Concentration Technique

Abstract This paper presents a novel hybrid approach to film cooling measurement, combining infrared (IR) thermography with the seed gas concentration technique. The seed gas concentration technique is used as an in-situ calibration ground truth for the IR measurements to correct for imperfect insulation and test facility-induced thermal disturbances, such as heat up of the coolant through viscous dissipation in the cavities as well as ingress and egress in the uncooled baseline case. This new approach allows the final film cooling results to inherit the advantages of both measurement techniques. The robustness against thermal disturbances, as well as the high accuracy, are inherited from the point-wise seed gas concentration technique, while the high spatial resolution is inherited from the full surface coverage IR measurements. This new approach is demonstrated for purge film cooling measurements in a turbine center frame (TCF) tested under Mach-similarity in the transonic test turbine facility (TTTF) at Graz University of Technology. The TCF, also known as intermediate turbine diffuser, is a stationary duct that connects the high-pressure turbine (HPT) to the low-pressure turbine (TCF) in modern high-bypass ungeared turbofan engines. The TCF was operated in an engine-representative 1.5-stage test vehicle, where a fully purged HPT was operating upstream of the TCF and a row of LPT vanes was situated downstream of the TCF. The herein investigated sources of film cooling are the purge flows that emanate from the hub cavities of the HPT. These hub purge flows bear significant cooling potential for the downstream TCF hub surface. The TTTF is a good example to showcase the benefits of this new measurement approach as the complexity of the rig is high, and the challenging boundary conditions imposed on the technique are representative of many continuously operated and high technology readiness level (TRL) turbine test facilities.