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978-3-8439-3498-5, Reihe Thermodynamik
Flow and heat transfer phenomena in a complex impingement system for integrally cooled turbine blades
281 Seiten, Dissertation Universität Stuttgart (2017), Softcover, A5
A novel jet impingement cooling concept was the focus of the present work. It was drafted to be integrated into the mid-chord section of a highly loaded turbine blade. The concept features a staggered jet and vent holes system through which the conditions inside the cooling cavity are established. In order to provide a fundamental understanding of the aerothermal characteristics for such an integral concept, the present work details the findings from a series of experimental investigations.
A baseline geometry setup served to gain principal insight into the concept’s flow and heat transfer properties. Continued investigations considered multiple geometry variants, studying the effects of, e.g., the alignment between the jet and vent holes, the extraction of cavity fluid through film holes, and the modification of heat transfer surfaces through dimples.
For the experimental investigations a test rig which incorporated the cooling passage model was used. The primary measurement techniques involved particle image velocimetry (PIV) and transient as well as steady-state liquid crystal thermography (TLC). Through these methods, spatially resolved flow field, heat transfer, and adiabatic surface temperature distributions were obtained. Additionally, steady-state and time-resolved pressure measurements were performed. Furthermore, a proper orthogonal decomposition analysis of the PIV data was undertaken to unveil hidden flow structures.
The baseline results reveal unique heat transfer characteristics for the passage walls, spanning a broad spectrum of heat transfer rates, which are exclusive to the complex flow field within the cooling passage. Relentlessly impinging jets induce high heat transfer rates on the respective target walls, forming local patterns unique to oblique impingement scenarios. Contrarily, flow regions in which fluid mixing is scarce effect areas of low heat transfer in the overall distributions. A sovereign feature of the passage’s flow field is denoted by the formation of a dominant center vortex. The present study successfully demonstrates that the basic heat transfer characteristics can be adjusted towards a more thermally balanced heat transfer situation despite the stringent geometric confinement. Hence, the extraction of cavity fluid through adequately placed film holes delineates an effective measure. This produces a remarkable increase in the local heat transfer for a region generally governed by low heat transfer rates.