EXPERIMENTAL AND NUMERICAL INVESTIGATION OF A NOVEL METHOD FOR GRADIENT TEMPERATURE MEASUREMENT

Hot gas temperature and mass flow rates are continuously increasing to meet future gas turbine power, efficiency and emission targets. Moreover, expectations for flexible operating capability can add conditions for frequent cold starts and load changes. To realize such gas turbine developments, improved cooling concepts are required to guarantee the lifetime of thermally highly loaded components such as turbine blades, vanes, blisks and combustor rings. In addition to design and metallurgical adjustments to the components, this also requires validated calculation and design methods. As described by Thiele et. al. [1], a visco-plastic material model has been developed which shows the significant influence of superimposed thermal gradients on the low-cycle failure life. Reliable temperature gradient measurements are required to validate the material models, FEM and CFD simulations and the fatigue life. Accurate in-situ measurement capability in real engine conditions is particularly challenging which existing measurement methods only cover to a limited extent. A novel application using Uniform Crystal Temperature Sensors (UCTS) with two different minimally invasive application methods is proposed and evaluated here. The sensor installation package is micro size, with a diameter that can be less than 1mm and a length that can be adjusted to the available wall thickness of the part and the expected gradient through the wall. Experimental work to validate the measurement accuracy of the UCTS was carried out using a highly efficient, patented radiation furnace reported in GTP- 18-1482, which can apply a heat flux of q >= 1.5 MW/m(2) and a thermal wall gradient of up to 65 K/mm. In order to validate the novel measurement system both experimentally and numerically, measurements with calibrated thermocouples and thermo-mechanical simulations were performed. For the temperature gradient data generation, the UCTS were integrated in a MAR-M247 hollow cylinder specimen in various configurations. The conventional cast nickel based alloy MAR-M247 is a typical turbine blade material. Its thermo-physical properties are well studied and it has been part of thermally loaded and temperature gradient investigations for several years. The paper focuses on the validation and application of the UCTS measurement system and shows its potential for investigating actual operating conditions of highly thermally loaded real engine components. Information from this study will be applicable to gas turbine design and development engineers needing in situ gradient measurements for rig or real engine testing programs.