Improving Turbine Cooling Through Control of Surface Roughness in the Additive Manufacturing Process
Open Access
- Author:
- Snyder, Jacob
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 28, 2019
- Committee Members:
- Karen Ann Thole, Dissertation Advisor/Co-Advisor
Karen Ann Thole, Committee Chair/Co-Chair
Stephen P Lynch, Committee Member
Robert Francis Kunz, Committee Member
Edward William Reutzel, Outside Member
Reid Adam Berdanier, Special Member - Keywords:
- L-PBF
gas turbines
heat transfer
additive manufacturing
surface roughness
DMLS
SLM
fluid flow
film cooling
process parameters - Abstract:
- Additive manufacturing (AM) offers the opportunity to transform a number of industries. With its increased design space, efficient material usage, and short turn-around times, many companies are already embracing the technology. The gas turbine industry in particular has a keen interest in the technology, as many of their components are highly engineered to survive extreme operating conditions. However, few users of AM are exploiting the process to its full potential. For example, the surface roughness inherent with the laser powder bed fusion (L-PBF) process, typically considered a weakness, can be used as an asset for convective heat transfer applications. To truly leverage AM for turbine cooling applications, a fundamental understanding of L-PBF surface roughness and its effect on cooling performance is required. Moreover, the extent to which the performance of cooling designs can be altered by changes to the parameters is essential to understand. This dissertation seeks to develop an understanding of the ways surface roughness inherent in the L-PBF process can be leveraged for convective heat transfer applications. An initial study investigated the effect of different process parameters on roughness and identified key physical interactions amongst the parameters. Additionally, alternate roughness scalings were proposed in an attempt to better predict formation of different types of roughness. With an understanding of the effect of the process parameters on roughness, a subsequent study focused on the effect of changing the parameters on internal and external turbine cooling configurations. The results showed that changes to the surface roughness brought about by changes to the process parameters had a significant impact on the performance of the geometries. For both internal and external cooling, changing the AM process parameters to reduce the surface roughness improved the overall performance. Using the parameters to control surface roughness was further explored by attempting to optimize the surface roughness for internal convection by varying combinations of process parameters. Results showed that small improvements to the performance could be achieved, mainly through changing the roughness magnitude of the channels. Additionally, combinations of parameters were identified that maintained a given performance but reduced build time. As an alternate method of controlling the surface roughness, a novel post-processing technique was also evaluated on an internal cooling geometry. Despite a high level of surface roughness in the as-built condition, the surface finishing technique was able to significantly reduce the roughness, resulting in an improvement to the cooling performance.