A Study of Mesh-Fed Slot Film Cooling

This investigation demonstrates the potential improvement in adiabatic film effectiveness that can be achieved through the use of mesh-fed surface slot film cooling. Mesh, or in-wall network, cooling is composed of fairly compact arrays of pedestals sized to fit within the limited wall thickness of a turbine airfoil. When the coolant discharge from such a mesh is along a shallow ramp to the airfoil aerodynamic surface (i.e., like an angled film hole), the resulting film effectiveness from this combined geometry can be very high. The in-wall mesh network acts as the structural means for obtaining the slot geometry. In this study, flat plate warm wind tunnel testing has been conducted on two mesh-fed film geometries and compared against data for a row of axial round film holes, as well as a row of shaped diffuser film holes. The mesh-fed geometries are composed of pedestal arrays with height-to-diameter ratios of 0.2 exiting onto 20-deg inclines to the surface. The mesh slot exit film blowing ratios tested ranged from $M=0.1$ to $M=0.7$⁠, while round and shaped film hole conditions covered 0.5 to 1.2. The mesh-fed film effectiveness results indicate a performance greater than that of shaped diffuser holes, but less than that of a more idealistic two-dimensional slot film geometry. The mesh-fed film effectiveness was as much as 25% higher than that for shaped holes in the near-hole region of $x/Ms<50$⁠, and up to 100% greater in the downstream region of $x/Ms>50$⁠.