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Experimental Study of Heat Transfer in Gas Turbine Blades Using a Transient Inverse Technique

To enhance specific power output and thermal efficiency of gas turbine engines, industry searches for ways to increase the turbine inlet temperatures. Therefore, temperatures of turbine blades increase as well and necessitate active cooling of these components. Experimental design work on such internal cooling schemes is carried out to find acceptable compromises between heat transfer and pressure losses. It is often carried out by using transient thermochromic liquid crystal techniques in combination with Plexiglas models. However, for real turbine blades this experimental technique is inappropriate due to the lack of optical access. Therefore, to study actual turbine blades there is need for development of noninvasive, nondestructive methodologies. This article describes a measurement technique that allows determination of internal heat transfer coefficients of real turbine blades experimentally. Thus, a test rig with a rapidly responding heater was designed to fulfill the requirement of a sudden increase in the air temperature within the cooling passages. The outer surface temperatures were measured using infrared thermography. To estimate the spatial distribution of internal heat transfer coefficients from transient surface temperatures the inverse heat transfer problem was solved. As optimization algorithm the Levenberg–Marquardt method was chosen. Outer surface temperature data was measured for a rectangular reference model with rib turbulators and compared with simultaneously acquired data using the thermochromic liquid crystal technique. It is concluded that the new experimental measurement technique could be used to quantitatively determine internal heat transfer coefficients.