60014 - Effects on Film Cooling Performance in the Showerhead From Geometric Parameterization of Shaped Hole Designs 

The occurrence of the highest heat loads at the leading-edge regions of turbine vanes and blades necessitates the most robust thermal protection, typically accomplished by densely packing film cooling holes in a “showerhead” arrangement. Traditionally, purely cylindrical holes have been used in laboratory studies of these cooling configurations; but recent research has shown that shaped holes provide more reliable thermal protection because of the superior coolant flow attachment to the exterior surface. Although this behavior has been observed in a handful of studies, the effects on cooling performance from varying the geometric details of the hole design are not well characterized. In this study, adiabatic effectiveness and off-the-wall thermal field measurements were conducted for two shaped hole geometries that were designed as successors to a baseline hole geometry presented in a previous study. The holes were built into the leading edge of a scaled-up turbine blade model used in a low-speed recirculating wind tunnel. The coolant was supplied to the showerhead via a pseudo-plenum feed used in a previous study in this facility to isolate the effects from hole geometry alone. It was found that a geometry with a 40% increase in area ratio resulted in only a marginal improvement in adiabatic effectiveness on the order of 10%. A design with a 12° forward and lateral expansion angle with a breakout area 40% larger had marginally worse performance than its matched area ratio counterpart (~15% lower), suggesting a negative sensitivity to breakout area. In all, these changes in performance for different shaped hole designs were small compared to the jump in performance from switching from a cylindrical hole to a shaped hole, which suggests a general insensitivity in performance to specific shaped hole details provided the coolant flow is well-attached to the surface.