Secondary flow and heat transfer coefficient distributions in the developing flow region of ribbed turbine blade cooling passages

This paper reports an experimental and numerical study of the development and coupling of aerodynamic flows and heat transfer within a model ribbed internal cooling passage to provide insight into the development of secondary flows. Static instrumentation was installed at the end of a long smooth passage, and used to measure local flow features in a series of experiments where ribs were incrementally added upstream. This improves test turnaround time while ensuring that the aerodynamic probe was non-invasive. Local heat transfer coefficient distributions were similarly captured using a hybrid transient liquid crystal technique. A composite heat transfer coefficient distribution for a 12 rib-pitch passage is reported: notably the behaviour is dominated by the development of the secondary flow in the passage throughout. Both the aerodynamic and heat transfer test data were compared to numerical simulations developed using a commercial computational fluid dynamics solver. By conducting a number of simulations it was possible to interrogate the validity of the underlying assumptions of the experimental strategy — their validity is discussed. The results capture the developing size and strength of the vortical structures in secondary flow. The local flow field was sensibly shown to be strongly coupled to the enhancement of heat transfer coefficient. Comparison of the experimental and numerical data generally show excellent agreement in the level of heat transfer coefficient predicted, though the numerical simulations fail to capture some local enhancement on the ribbed surfaces. Where this was the case the coupled flow and heat transfer measurements were able to identify missing velocity field characteristics.Copyright © 2014 by ASME