Interaction of Film Cooling Rows: Effects of Hole Geometry and Row Spacing on the Cooling Performance Downstream of the Second Row of Holes

A comprehensive set of generic experiments is conducted to investigate the interaction of film cooling rows. Five different film cooling configurations are considered on a large-scale basis each consisting of two rows of film cooling holes in staggered arrangement. The hole pitch to diameter ratio within each row is kept constant at $P/D=4.$ The spacing between the rows is either $x/D=10,$ 20, or 30. Fan-shaped holes or simple cylindrical holes with an inclination angle of 30 deg and a hole length of 6-hole diameters are used. With a hot gas Mach number of $Mam=0.3,$ an engine like density ratio of $ρc/ρm=1.75,$ and a freestream turbulence intensity of $Tu=5.1%$ are established. Operating conditions are varied in terms of blowing ratio for the upstream and, independently, the downstream row in the range $0.5<M<2.0.$ The results illustrate the importance of considering ejection into an already film-cooled boundary layer. Adiabatic film cooling effectiveness and heat transfer coefficients are significantly increased. The decay of effectiveness with streamwise distance is much less pronounced downstream of the second row primarily due to pre-cooling of the boundary layer by the first row of holes. Additionally, a comparison of measured effectiveness data with predictions according to the widely used superposition model of Sellers is given for two rows of fanshaped holes.