Dependence of Film Cooling Effectiveness on 3D Printed Cooling Holes

As additive manufacturing (AM) technologies utilizing metal powders continue to mature, the usage of AM parts in gas turbine engines will increase. Current metal AM technologies produce parts with substantial surface roughness that can only be removed from external surfaces and internal surfaces that are accessible for smoothing. Difficulties arise in making smooth the surfaces of small internal channels, which means the augmentation of pressure loss and heat transfer due to roughness must be accounted for in the design. As gas turbine manufacturers have only recently adopted metal AM technologies, much remains to be examined before the full impacts of applying AM to turbine parts are understood. Although discrete film cooling holes have been extensively studied for decades, this objective of this study was to understand how the roughness of film cooling holes made using AM can affect the overall cooling effectiveness. Coupons made from a high temperature nickel alloy with engine-scale film holes were tested in a rig designed to simulate engine relevant conditions. Two different hole sizes and two different build directions were examined at various blowing ratios. Results showed that the effectiveness is dependent on the build direction and the relative size of the hole. It was also discovered that commercially available AM processes could not reliably produce small holes with predictable behavior.

Section: Review Of Literaturementioning

confidence: 99%

Effectiveness Measurements of Additively Manufactured Film Cooling Holes

Stimpson

Snyder

Thole

et al. 2017

Geometrical Parameter Effects on Film-Cooling Effectiveness of Rectangular Diffusion Holes

Liu

Zhou

2017

This paper presents an experimental investigation of the rectangular diffusion hole. The effects of rectangular aspect ratio and lateral diffusion angle on film-cooling effectiveness were studied at a low-speed flat-plate experimental facility. The pressure-sensitive paint (PSP) measurement technique was employed to determine the adiabatic effectiveness. The experiments were performed at a density ratio of DR = 1.38 and a mainstream turbulence intensity of Tu = 3.5%. The blowing ratio was varied from M = 0.5 to M = 2.5. Three aspect ratios and three lateral diffusion angles were chosen to match the semicircle and straight-line sidewall shape of the rectangular cross section. A comparative investigation was performed among a typical fan-shaped hole and ten rectangular diffusion holes. The experimental results exhibited diversified film distribution patterns of the rectangular diffusion hole, including single-, bi-, and tripeak patterns. The overall cooling effectiveness increased with the increase of rectangular aspect ratio. The improved magnitude was amplified as blowing ratio increased. The holes with semicircle sidewall were shown to be more suitable for high blowing ratio conditions. The maximum increase of cooling effectiveness was over 70% compared to the fan-shaped hole. The reduction of the lateral diffusion angle affected the film distribution pattern significantly, thereby influencing the cooling effectiveness. To obtain a fixed coverage ratio of film hole row, the rectangular diffusion hole with a larger cross-sectional aspect ratio and a slightly smaller lateral diffusion angle is a preferred scheme.

Effects of Inclination Angle, Orientation Angle, and Hole Length on Film Cooling Effectiveness of Rectangular Diffusion Holes

Liu

Zhou

2018

Film-cooling effectiveness of rectangular diffusion holes under an inclination angle α = 45 deg, an orientation angle β = 45 deg, and a length-to-diameter ratio of L/D = 8.5 were, respectively, examined in a flat-plate experimental facility using the pressure sensitive paint (PSP) technique. Experiments were performed at a density ratio of DR = 1.38 and a mainstream turbulence intensity of Tu = 3.5%. The semicircle sidewall rectangular diffusion hole varied at three cross-sectional aspect ratios, i.e., AS = 3.4, 4.9, and 6.6. The tested results were compared with the baseline design with an inclination angle α = 30 deg, an orientation angle β = 0 deg, and a length-to-diameter ratio L/D = 6. A three-dimensional (3D) numerical simulation method was employed to analyze the flow field. The experimental results showed that the increased inclination angle converted the bi- or tri-peak effectiveness pattern of the baseline design to a single-peak pattern, weakened the lateral diffusion of coolant, and consequently decreased cooling effectiveness obviously. The decreased magnitude amplified with the increase of cross-sectional aspect ratio and blowing ratio. The adding of orientation angle seriously weakened the cooling effectiveness of the baseline design, and the blowing ratio and cross-sectional aspect ratio had almost no effect on overall cooling effectiveness. The elongated hole length provided a uniform distribution of lateral cooling effectiveness, which produced differential effects on the bi- or tri-peak pattern. The elongated hole length decreased the cooling effectiveness on the near hole region, but had less effects on overall cooling effectiveness, except the high blowing ratio.