In the present study film cooling effectiveness and heat transfer were systematically investigated on a turbine NGV airfoil employing the transient liquid crystal technique and a multiple regression procedure. Tests were conducted in a linear cascade at exit Reynolds numbers of 0.52e6, 1.02e6 and 1.45e6 and exit Mach numbers of 0.33, 0.62 and 0.8, at two mainstream turbulence intensities of 5.5 and 10 percent. The film cooling geometry consisted of a single compound angle row on the pressure side (PS), and a single or a double row on the suction side (SS). Foreign gas injection was used to obtain a density ratio of approximately 1.65, while air injection yielded a density ratio of unity. Tests were conducted for blowing ratios of 0.25 to 2.3 on the SS, and 0.55 to 7.3 on the PS. In general film cooling injection into a laminar BL showed considerably higher effectiveness in the near-hole region, as compared to a turbulent BL. While mainstream turbulence had only a weak influence on SS cooling, higher effectiveness was noted on the PS at high turbulence due to increased lateral spreading of the coolant. Effects of mainstream Mach and Reynolds number were attributed to changes of the BL thickness and flow acceleration. Higher density coolant yielded higher effectiveness on both SS and PS, whereas heat transfer ratios were increased on the SS and decreased on the PS. Comparison of the single and double row cooling configurations on the SS revealed a better film cooling performance of the double row due to an improved film coverage and delayed jet separation.

This paper presents heat transfer measurements on a turbine airfoil in a linear cascade at various exit Reynolds and Mach numbers ranging from 3.2e5 to 1.6e6 and 0.2 to 0.8, respectively, which have been conducted with the transient liquid crystal technique. Two series were performed at turbulence intensities of 5.5% and 10%, the latter being created by a squared-bar mesh placed 10 meshsizes upstream of the turbine airfoils. While normally polished liquid crystals were used additional experiments were done at the high turbulence intensity with naturally rough liquid crystals. All measurements indicate a gradual increase in heat transfer and an upstream shift of the laminar-to-turbulent transition with increasing Reynolds number and turbulence intensity. The leading edge heat transfer agrees well with correlations if the turbulence length scale is taken into account. The measurements conducted with rough liquid crystals show an earlier transition on the suction side. Calculations with a two-dimensional boundary layer code agree well with the measurements.

The transient liquid crystal technique has been used to measure film cooling effectiveness and heat transfer on a flat plate in a free jet, and a turbine airfoil in a linear cascade. A multiple-test regression method has been developed for the data reduction, considering a transient coolant temperature evolution. Flat plate film cooling was investigated for a single row of 35° inclined holes at Mach numbers of 0.3 and 0.5, and two turbulence intensities. Downstream of injection heat transfer was increased in-between the holes due to enhanced turbulence caused by the shearing of the coolant and the mainstream. At higher turbulence intensity the range of blowing ratios was broader as lift-off was delayed. Rim cooling measurements on the airfoil were conducted at engine-representative flow conditions. A maximum effectiveness of 0.3 behind injection was observed on the suction side, with slightly higher values for a double row in comparison to a single row configuration. Due to a high coolant momentum, the effectiveness on the pressure side was very low at about 0.05 for a single row configuration.

In the present study the aerodynamic performance of a turbine NGV airfoil was investigated, cooled from several showerhead, pressure and suction side stations. Film cooling heat transfer and effectiveness on this airfoil was examined in part I of this paper. Tests were conducted in a linear cascade at an exit Reynolds number of 1.45e6 and an exit Mach number 0.8. Density ratio effects were studied with air and CO 2 injection, matching the densities by correctly adjusting the coolant temperature.In terms of a primary loss coefficient, neglecting the coolant kinetic energy, coolant injection increased the losses by 20-30% compared to solid blade losses, but depended only weakly on the coolant mass flow rate. A slight loss increase for increasing injection up to 2% coolant mass flow was noted, followed by a weak decrease for further augmented coolant mass flow rates. The primary losses appeared to be independent of the coolant medium and temperature.Thermodynamic loss coefficients including the loss of coolant kinetic energy, monotonically increased with coolant mass flow rates. To check the validity of CO 2 injection for the simulation of high density ratios, the latter has been matched using strongly cooled air and heated CO 2 . The thermodynamic losses did not match at constant density ratio, but at constant coolant Mach number, when compared at constant coolant mass flow rates. Reporting the losses to the total pressure ratio (momentum flux ratio) yielded excellent scaling emphasizing the usefulness of the momentum flux ratio for film cooling loss scaling.

An investigation of effectiveness and heat transfer on a cylinder model with showerhead cooling has been conducted in a free jet test facility, using the transient liquid crystal technique. A three- and a four-row configuration, covering a region of ±21°, were chosen to study the cooling behaviour for zero and off-design incidences. Typical engine airfoil leading edge conditions were maintained for the freestream Reynolds and Mach numbers to 1.55e5 and 0.26 for the three-row, and 1.84e5 and 0.30 for the four-row configuration, at a turbulence intensity of 7%. The blowing and momentum rates ware varied from 0.4 to 1.8 and 0.1 to 1.9, at a density ratio of 1.65. At zero incidence it could be observed for both configurations that the highest effectiveness of about 0.3 was achieved at a blowing rate of 0.4. Negative incidence for the four-row configuration resulted in much higher effectiveness, being as high as 0.5 at a blowing rate of 0.9, with an associated high heat transfer. Much lower effectiveness was achieved at positive incidence, where the blowing rate of 0.9 showed the best cooling behaviour. Higher effectiveness — but also increased heat transfer — was in general observed for the four-row configuration, with a 60% higher massflow.