An experimental study was conducted to investigate the film cooling performance on the suction side of a first-stage turbine vane. Tests were conducted on a nine times scale vane model at density ratios of DR=1.1 and 1.6 over a range of blowing conditions, 0.2⩽M⩽1.5 and 0.05⩽I⩽1.2. Two different mainstream turbulence intensity levels, Tu∞=0.5 and 20 percent, were also investigated. The row of coolant holes studied was located in a position of both strong curvature and strong favorable pressure gradient. In addition, its performance was isolated by blocking the leading edge showerhead coolant holes. Adiabatic effectiveness measurements were made using an infrared camera to map the surface temperature distribution. The results indicate that film cooling performance was greatly enhanced over holes with a similar 50 deg injection angle on a flat plate. Overall, adiabatic effectiveness scaled with mass flux ratio for low blowing conditions and with momentum flux ratio for high blowing conditions. However, for M<0.5, there was a higher rate of decay for the low density ratio data. High mainstream turbulence had little effect at low blowing ratios, but degraded performance at higher blowing ratios.

There have been numerous studies of film cooling performance for the downstream coolant holes on a turbine airfoil using test geometries ranging from flat plates to airfoils. Most of these studies simulate a relatively unperturbed boundary layer flow approaching the coolant holes. This stimulated the current inquiry into the effects of realistic upstream conditions for downstream coolant holes. To investigate this, a series of experiments were performed focussing on the first downstream row of holes on the pressure side of a typical turbine vane. The film cooling effectiveness for this pressure side row of holes was determined subject to no showerhead blowing, and to showerhead blowing with varying blowing rates. Furthermore, tests were conducted with low and high freestream turbulence levels. For this investigation, a leading edge showerhead array of six film cooling rows was utilized, with coolant from three of these rows being directed towards the pressure side of the vane. For all experiments a coolant to freestream density ratio of nominally DR = 1.8 was used. Adiabatic effectiveness was determined from surface temperature measurements for a nominally adiabatic surface using an infrared camera for spatially resolved mapping of the surface temperature. This study showed that showerhead injection had a dominant influence on the adiabatic effectiveness performance of downstream cooling. Showerhead injection appeared to cause a significant increase in coolant jet dispersion, presumably by increased levels of turbulence. Even when the freestream turbulence level at the pressure side coolant holes was increased to 17%, showerhead injection caused a significant degradation in the film cooling performance of the pressure side row of holes. Because of the increased dispersion caused by the showerhead injection for the pressure side coolant jets, the superposition model failed to correctly predict adiabatic effectiveness levels for combined showerhead and pressure side coolant injection.

The process of film cooling is known to severely disturb the boundary layer around a turbine airfoil. Since most film-cooled airfoils have more than one injection station, the flow field approaching a row of film cooling holes could be altered by the presence of an upstream cooling station. To investigate this possibility, an experimental investigation was conducted on the suction side of a scaled-up turbine vane. Adiabatic effectiveness measurements were made downstream of a single row of cooling holes both with and without the upstream showerhead holes operating. A range of suction side blowing ratios, 0.3 ≤ M ≤ 1.3, were investigated with large-scale mainstream turbulence intensities of Tu∞ = 0.5% and Tu∞ = 21%. The effects of the showerhead coolant were evaluated at an engine-typical showerhead blowing ratio of Msh = 1.6, with three of the six rows of cooling holes in the showerhead directed towards the suction side of the airfoil. Experiments were conducted with a coolant-to-mainstream density ratio of DR = 1.6. An infrared camera was used to obtain spatially-resolved surface temperature measurements, which were corrected for conduction effects and converted to adiabatic effectiveness. The results showed that showerhead coolant had a strong impact on suction side adiabatic effectiveness levels under low mainstream turbulence. Although effectiveness levels increased with the showerhead operating, the suction side coolant jets increased dispersion of the showerhead coolant. Under high mainstream turbulence conditions, there was very little interaction between the showerhead coolant and the suction side coolant jets. Adiabatic effectiveness levels were considerably lower than those for the low turbulence case, which was partially due to increased dispersion of the showerhead coolant upstream of the suction side holes. The superposition model over-predicted adiabatic effectiveness levels under low mainstream turbulence conditions, but was very effective in predicting the combined performance of the showerhead and the suction side cooling holes under high mainstream turbulence conditions.