Abstract
Shaped holes are considered as an effective solution to enhance gas turbine film-cooling performance, as they allow to increase the coolant mass-flux, while limiting the detrimental lift-off phenomena. A great amount of work has been carried out in past years on basic flat plate configurations while a reduced number of experimental works deals with a quantitative assessment of the influence of curvature and vane pressure gradient. In the present work PSP (Pressure Sensitive Paint) technique is used to detail the adiabatic effectiveness generated by axial shaped holes with high value of Area Ratio close to 7, in three different configurations with the same 1:1 scale: first of all, a flat plate configuration is examined; after that, the film-cooled pressure and suction sides of a turbine vane model are investigated. Tests were performed varying the blowing ratio and imposing a density ratio of 2.5 . The experimental results are finally compared to the predictions of two different correlations, developed for flat plate configurations.
Highlights
To prevent jet lift-off and a loss of film efficiency, film cooling schemes of vane and blade generally adopt fan shaped film holes instead of standard cylindrical holes at the cost of increasing manufacturing complexity
It must be considered that the level of knowledge of shaped holes performances drops considerably when the focus is shifted from flat plates to turbine vane/blade configurations
Adiabatic effectiveness measurements were carried out, by means of pressure sensitive paint (PSP) technique, on a film-cooled plate and a 2D turbine vane model; the fan shaped hole geometry selected for the present research was characterised by a high value of Area Ratio not covered by the validity range of available correlations
Summary
To prevent jet lift-off and a loss of film efficiency, film cooling schemes of vane and blade generally adopt fan shaped film holes instead of standard cylindrical holes at the cost of increasing manufacturing complexity. Barigozzi et al [12] and Gritsch et al [13] showed that an increase in Mach number (i.e., flow acceleration) could be beneficial to the film coverage, as the positive stream-wise pressure gradient creates higher velocities in the boundary layer and keeps the jets closer to the surface Despite these thorough investigations, the early-stage design of film cooling system on vane/blade surface generally adopts, because of their simplicity, correlations developed on flat plate test rig, missing the effects of pressure gradient and curvature. The shaped holes geometry was selected with a high value of Area Ratio (around 7), beyond the typical values considered by published correlations These correlations were stressed on the experimental results to check their prediction capability on both the flow stands (i.e., with and without the effect of curvature and pressure gradients)
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