HIGH SPEED ROTATING HPT BLADE THERMAL IMAGING OF A FULL SCALE COOLED 1+1/2 STAGE TURBINE IN A SHORT DURATION TRANSIENT TEST FACILITY

This paper presents results from original development of a long wavelength infrared (LWIR) high pressure turbine (HPT) blade thermal imaging system on a Full Scale Cooled 1+1/2 Stage Rotating Turbine in the Air Force Research Laboratory Turbine Research Facility (TRF) at WPAFB, OH. The TRF is a short duration transient turbine blowdown rig capable of matching relevant non-dimensional parameters such as Reynolds Number, Prandtl Number, corrected speed, along with cooling pressure ratios. A LWIR HPT blade thermal imaging camera and custom optical probe are carefully designed and installed to capture transient surface temperatures across a 46-blade rotor arranged in a rainbow wheel of cooled and uncooled airfoils. Over ten transient rotating turbine tests were run acquiring rotating HPT blade images from four different rotor blade views at full RPM. Lessons are shared regarding signal-to-noise challenges of fast transient rotor IR measurements. Together, data from these views show different transient thermal gradients across cooled and uncooled airfoils, revealing insight into cooling flow circumferential platform leakage, and film cooling variations under varying backflow margin. Transient thermal images are also captured showing the effects of momentary hot gas ingestion and film cooling recovery. Furthermore, this paper demonstrates the ability to locate individual subsurface blocked cooling hole passages that do not appear in borescope inspection. This experiment is the first to show such behavior on a full-scale rotor at full RPM in the TRF.