<p>Additive manufacturing processes, such as direct metal laser sintering (DMLS), enable creation of novel turbine cooling internal passages and systems. However, the DMLS method produces a significant and unique surface roughness. Previous work in scaled passages analyzed pressure losses and friction factors associated with the rough surfaces as well as investigated the velocity profiles and turbulent flow characteristics within the passage. In this study, the heat transfer characteristics of scaled additively manufactured surfaces were measured using infrared thermography. Heated roughness panels were CNC machined from a block of aluminum 6061 to create a near isothermal surface.&nbsp; Fluid resistance differences between the aluminum roughness panels and roughness panels constructed from ABS plastic using the same roughness patterns from McClain et al. (2020) are investigated.&nbsp; The resulting convection measurements compare reasonably to the correlations presented by Gneilinski (1976) and Stimpson et al. (2017). The additively manufactured surfaces are also investigated computationally using a Reynolds Averaged Navier Stokes (RANS)-based Computational Fluid Dynamic (CFD) method and the results are compared with the measurements. CFD is used in order to gain a fuller picture of how the flow and rough surfaces interact to modify the skin friction and convective heat transfer performance and to characterize the streamwise evolution and near-wall inhomogeneity of the flow. Finally, the overall thermal performance enhancements and friction losses are assessed through calculation of a surface averaged thermal performance parameter. The thermal performance results indicate results in-line with those found for traditional commercial roughness.&nbsp; The passages investigated in this study do not include long-wavelength artifacts and channel geometric deviations observed by Wildgoose et al. (2020).&nbsp; However, the results of this study indicate that, based on the roughness augmentation alone, artificial convective cooling enhancers such as turbulators or dimples may still be required for additively manufactured turbine component cooling.</p>

Convection in Scaled Turbine Internal Cooling Passages With Additive Manufacturing Roughness

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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