The ever-increasing trend in gas turbine performance is mainly driven by the growth of turbine inlet temperature. This in turn leads to augmented thermal loads for the engine components, which are usually managed thanks to the introduction of complex internal cooling systems. Typical experimental methods for assessing the heat transfer characteristics of such systems commonly rely upon scaled-up models investigated at nearly ambient conditions, since the size and operating environment of real engine parts make it extremely difficult to perform direct measurements. By doing so, however, many geometric and flow features of the real cooling system get lost, since the studied geometry is ideal and measurement constraints often require a simplification of the system itself. A much more reliable evaluation of cooling performance would thus be obtained by studying the real hardware, which requires the development of a suitable technique. As an additional advantage, a similar method could also be employed for in-line inspection of manufactured parts, as to clearly identify faults and defects before the actual installation.

The aim of this work is to present the development and application of a measurement technique that allows to record internal heat transfer features of real components. In order to apply this method, based on similar approaches proposed in previous literature works, the component is initially heated up to a steady temperature, then a thermal transient is induced by injecting cool air in the internal cooling system. During this process, the external temperature evolution is recorded by means of an IR camera. Experimental data are then exploited to run a numerical procedure, based on a series of transient finite-element analyses of the component. In particular, the test duration is divided into an appropriate number of steps and, for each of them, the heat flux on internal surfaces is iteratively updated as to target the measured external temperature distribution. Heat flux and internal temperature data for all the time steps are eventually employed in order to evaluate the convective heat transfer coefficient via linear regression. This technique has been successfully tested on a cooled high-pressure vane of a Baker Hughes heavy-duty gas turbine, which was realised thanks to the development of a dedicated test rig at the University of Florence, Italy. The obtained results provide sufficiently detailed heat transfer distributions in addition to allowing to appreciate the effect of different coolant mass flow rates. The methodology is also capable of identifying defects, which is demonstrated by inducing controlled faults in the component.


Development and Application of an Internal Heat-Transfer Measurement Technique for Cooled Real Engine Components

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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