Stagnation region heat transfer coefficients are obtained from jet impingement onto a concave surface in this experimental investigation. A single row of round jets impinge on the cylindrical target surface to replicate leading edge cooling in a gas turbine airfoil. A modified, transient lumped capacitance experimental technique was developed (and validated) to obtain stagnation region Nusselt numbers with jet-to-target surface temperature differences ranging from 60 °F (33.3 °C) to 400 °F (222.2 °C). In addition to varying jet temperatures, the jet Reynolds number (5000–20,000), jet-to-jet spacing (s/d = 2–8), jet-to-target surface spacing (ℓ/d = 2–8), and impingement surface diameter-to-jet diameter (D/d = 3.6, 5.5) were independently varied. This parametric investigation has served to develop and validate a new experimental technique, which can be used for investigations involving large temperature differences between the surface and fluid. Furthermore, the study has broadened the range of existing correlations currently used to predict heat transfer coefficients for leading edge jet impingement.

A numerical investigation of leading edge impingement is completed in this study. Impingement onto a half cylinder, concave surface is used to model the leading edge of a modern gas turbine airfoil. The temperature difference between the impinging jet and the target surface is varied from ΔT = 60°F (33.3°C) (typical of traditional laboratory experiments) to ΔT = 1000°F (555.6°C) (representative of temperature differences encountered in modern engines). Over this range of temperatures, the simulations are validated against experimental data and extended to engine-like conditions. In addition to the varying temperatures, the effect of jet Reynolds number is also investigated (Rejet = 5000–25000). The jet geometry is also varied in this investigation to model the effect of jet-to-jet spacing (s/d = 2–8), the effect of jet–to–target surface distance (ℓ/d = 2–8.5), and the effect of target surface diameter (D/d = 3.6 and 5.5). For all simulations the k-ω, Shear Stress Transport (SST) turbulence model is used to simulate the impingement flows. Over the range of flow conditions and geometry variations, the SST model is proven to be effective in predicting leading edge heat transfer coefficients. With multiple direct comparisons between the numerical simulations and existing experimental data, the simulations predict the surface Nusselt numbers within an average of 11% of the experimental data. Furthermore, the predictions indicate the existing correlations developed in low temperature laboratory experiments are sufficient for calculating stagnation region Nusselt numbers under engine-like temperatures.

Detailed film cooling effectiveness distributions are obtained on a flat plate using the pressure sensitive paint (PSP) technique. The effects of average blowing ratio (M = 0.25–1.0) and coolant – to – mainstream density ratio (DR = 1.0–1.4) are evaluated in a low speed wind tunnel with a freestream velocity of 8.5 m/s and a freestream turbulence intensity of 6.8%. The coolant – to – mainstream density ratio is varied by using either nitrogen (DR = 1.0) or argon (DR = 1.4) as the coolant gases. The double hole geometry consists of a row of simple angle (θ = 35°), cylindrical holes coupled with one row of compound angle holes (θ = 45°, β = 50°). With the selected geometry, the compound holes effectively weaken the counter rotating vortex pair formed within the traditional simple angle hole. Therefore, the surface film cooling effectiveness is increased compared to a single row of simple angle film cooling holes. While increasing the blowing ratio decreases the film cooling effectiveness, the severity of the film cooling effectiveness reduction is less than with the single row of holes.

Stagnation region heat transfer coefficients are obtained from jet impingement onto a concave surface in this experimental investigation. A single row of round jets impinge on the cylindrical target surface to replicate leading edge cooling in a gas turbine airfoil. A modified, transient lumped capacitance experimental technique was developed (and validated) to obtain stagnation region Nusselt numbers with jet-to-target surface temperature differences ranging from 60°F (33.3°C) to 400°F (222.2°C). In addition to varying jet temperatures, the jet Reynolds number (5000–20000), jet-to-jet spacing (s/d = 2–8), jet-to-target surface spacing (ℓ/d = 2–8), and impingement surface diameter-to-jet diameter (D/d = 3.6, 5.5) were independently varied. This parametric investigation has served to develop and validate a new experimental technique which can be used for investigations involving large temperature differences between the surface and fluid. Furthermore, the study has broadened the range of existing correlations currently used to predict heat transfer coefficients for leading edge, jet impingement.