Louver and effusion cooling heat transfer for a double wall effusion plate with impingement jet array coolant supply

•Louver slot cooling is employed so that cooling air advects as a protective layer downstream along the test surface.•Line-averaged adiabatic effectiveness results show that louver and effusion cooling arrangement often provides higher effectiveness, relative to an effusion cooling only arrangement.•An advantage of the louver slot is more uniform values of increased effectiveness along the entire test surface, including locations which are just downstream of the slot.•Relatively weak dependence on blowing ratio is present for the louver and film cooling arrangement, in contrast to the effusion only configuration.•For blowing ratios of 5.2 to 5.5, louver and effusion cooling gives lower line-averaged heat transfer coefficients (relative to effusion cooling only) because of reduced local turbulent thermal transport levels within wakes downstream of louver leap device.