Flow in a Simulated Turbine Blade Cooling Channel With Spatially Varying Roughness Caused by Additive Manufacturing Orientation

Abstract

Additively manufactured surfaces that are pointed upward have been shown to exhibit roughness characteristics different from those seen on surfaces that point downward. For this investigation, the Roughness Internal Flow Tunnel (RIFT) and computational fluid dynamics models were used to investigate flow in channels with different roughness on opposing walls of the channel. Three rough surfaces were employed for the investigation. Two of the surfaces were created using scaled, structured-light scans of the upskin and downskin surfaces of an Inconel 718 component which was created at a 45-deg angle to the printing surface. A third rough surface was created for the RIFT investigation using a structured-light scan of a surface similar to the Inconel 718 downskin surface, but a different scaling was used to provide larger roughness elements in the RIFT. The resulting roughness dimensions (Rq/Dh) of the three surfaces used were 0.0064, 0.0156, and 0.0405. The friction coefficients were measured over the range of 10,000 < ReDh < 70,000 for each surface opposed by a smooth wall and opposed by each of the other rough walls. X-array hot film anemometry was used to characterize the velocity and turbulence profiles for each roughness combination. The results of inner variable analysis demonstrate that the roughness function (ΔU+) becomes independent of the roughness condition of the opposing wall providing evidence that Townsend's Hypothesis holds for the relative roughness values expected for additively manufactured turbine-blade cooling passages.

Flow in additively manufactured super-rough channels

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Figure 9.Velocity profiles in Ch10-R4, Ch20-R4, Ch30-R4 and Ch30-R2. The symbols in ( a – c ) are hot-wire measurements at one streamwise–spanwise location (McClain et al., 2021). The shaded regions show the variations of the time-averaged streamwise velocity in the domain.

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“…The horizontal size of the rough surfaces is , where is the intended half-channel height. Further details of the three rough surfaces can be found in McClain et al. (2021), where the three rough surfaces are referred to as up-skin, down-skin and realx102, respectively.…”

“…(We reserve the symbol for half-channel height.) ( b ) A spanwise–wall-normal cross-section of an additively manufactured channel (Bons, Taylor, McClain, & Rivir, 2001; McClain et al., 2021). The red and blue lines are the surface roughness; and are the intended bottom- and top-wall locations (when manufacturing the channel); and are the trough locations of the bottom and top surface roughness; and are the peak locations of the bottom and top surface roughness.…”

“…An objective of this work is to re-evaluate the claims in Stafford et al. (2021) and McClain et al. (2021).…”

“…In more traditional subtractive manufacturing, whatever process is used to machine the channel can be used to finish the surface and remove large-scale roughness. This, however, is often not possible for additively manufactured cooling channels because (Bons, Taylor, McClain, & Rivir, 2001;McClain et al, 2021). The red and blue lines are the surface roughness; y b and y t are the intended bottom-and top-wall locations (when manufacturing the channel); y b− and y t− are the trough locations of the bottom and top surface roughness; y b+ and y t+ are the peak locations of the bottom and top surface roughness.…”