Gas turbine vanes find themselves in very hostile environments – extremely high temperature combustion gases, much exceeding material melting temperatures, flowing over them at enormous pressures. It is necessitated due to the increased efficiency and power output at these conditions. However, this also means that, in spite of the technological advancements made, these parts need frequent repairing compared to parts placed in milder environments. Primarily due to economic reasons, gas turbine parts are repaired by companies other than the original equipment manufacturer (OEM). While multitude of condition monitoring techniques have been developed and are used in the industry for regular maintenance checks, there is no easy way to characterize the impact on thermal performance of the repairing processes involved. This thesis reports the development of a technique to address this issue. It also chronicles the test rig design, experiments conducted, development and significance of the thermal performance metric. Heated air (250 ̊C – 300 ̊C) is flown through the internal cooling passages of 8 samples each of OEM and repaired parts at two different pressure ratios (vane inlet over ambient pressure), 1.1 and 1.3. First, steady state mass flow rates through each airfoil (one part is a cluster of 4 airfoils) is experimentally determined and compared among the OEM and repaired sample sets. Second, a transient experiment is run and the surface temperatures of the airfoils are measured using multiple infrared cameras viewing both the pressure and suction side of the airfoils. A parameter involving localized vane surface temperature, airfoil inlet temperature and ambient temperature is formulated to characterize the vane thermal performance. Using statistical analysis, it is found that there is no significant difference between the OEM and repaired samples tested. The development of the discussed technique, it is expected, will help companies in the gas turbine vane repairing business to qualify their parts in a robust and efficient manner without the need to invest a lot of money in buying precision equipment, or, control chambers. Finally, a couple of further studies are recommended to further improve the qualifying procedure and thereby increase the efficiency of the technique. / Master of Science / Most manufactured parts, during its lifetime, go through wear and tear of some form. Some much more than others – a gas turbine vane is one example, owing to the hostile environments it finds itself in. While repairing turbine vanes make economic sense instead of replacing the worn-out vanes with new ones, due care must be taken to ensure that the repairs pass high quality standards of the original manufactured parts. Most, if not all, companies in the turbine repairing business rely on room-temperature air-flow testing through the internal passages of these vanes to qualify their repaired parts. This is done partly due to the complexity in replicating engine-like conditions in a test environment in addition to being very time-intensive. While room-temperature air flow comparison between repaired and original parts is a necessary test, it does not paint the whole picture. Thermal performance, or, how the vane exchanges heat with the surrounding media, is the other part which completes the puzzle. A plurality of techniques has been developed to ascertain the thermal performance of gas turbine vanes, however, these are limited in the scope of their applicability – the reason why industry is still mostly relying on airflow measurements for their part qualification. In this study, a new technique has been proposed which is agnostic of the unavoidable variations in operating conditions and easy to apply while still upholding high quality standards. This translates to huge savings to organizations which are in the business of repairing original parts, not necessarily restricted to gas turbine industry.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/82492 |
| Date | 13 March 2018 |
| Creators | Chowdhuri, Shubham |
| Contributors | Mechanical Engineering, Ekkad, Srinath V., Qiao, Rui, Ng, Wing Fai |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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