Additive Manufacturing (AM) is a process for making complex parts that were once difficult to machine using traditional manufacturing processes such as forging, casting, and welding. As a new and promising processing technology, AM is being increasingly applied to the manufacturing of high temperature turbine parts. However, before the widespread application of AM can become feasible, the influence of such processes on the performance of turbine hot ends — especially during the film cooling flow heat transfer — requires further study.

This paper focuses a large eddy simulation study done in order to understand the physical phenomena involved in the random roughness caused by the AM of fan-shaped film holes. This paper proposes a set of workflows to connect the AM, CFD simulation, Computed Tomography (CT) and reverse modeling, so that the effect of AM on the flow and heat transfer of film cooling can be studied.

The results of this preliminary workflow reveal several observations. First, that the film cooling effectiveness (η) of AM fan-shaped holes decreases. The area averaged η of the ideal hole is 0.32, while the area averaged cooling effectiveness of the AM hole is 0.29. As such, the η of the AM fan-shaped hole has a significant bifurcation phenomenon. This is because the separation bubble in-tube moves forward, and blocks the flow channel, which bifrucates the flow in-tube. Second, a pressure gradient towards the trailing edge generated at a random rough surface near the leading edge squeezes the fluid. The combined effect of these two mechanisms causes the fluid to flow out of the air film pores mainly from the leading edge with a smaller lateral expansion.

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