Tomographic flow measurements over additively manufactured cooling channel roughness

Additive manufacturing (AM) offers many potential advantages to constructing gas turbine components such as allowing for more complex geometry in carefully optimized designs. AM processes, such as direct laser sintering, create roughness with distinct characteristics including periodicity from layers of fused material and varying roughness element size depending on surface print orientation. Understanding how this affects airflow through micro cooling channels is essential for component design. Individual roughness elements may block up to 15% of a cooling channel. The fluid responses to this level of roughness are difficult to characterize using traditional models. Three test surfaces were constructed using CT scans of a micro cooling channel printed in Inconel 718 and Hastelloy-X to act as the floor of the roughness internal flow tunnel (RIFT) wind tunnel. These surfaces included an Upskin and Downskin surface to contrast roughness variation caused by print orientation. A tomographic particle tracking system was constructed to examine a 40 x 40 x 6 mm section of the RIFT with the goal of providing a more detailed analysis of flow behavior over roughness elements than previous studies. This system uses a micro bubble generator to provide seed particles, a 15 Hz Evergreen laser, and four 8 MP cameras mounted horizontally to view the test volume. Detailed particle tracking velocimetry measurements of flow around individual roughness elements including velocities, Reynolds stress and dispersive stress above the rough surface are discussed within the limitations of the particle tracking system.