Large-scale experimental study of the turbulent flow over an effusion cooling plate*

Used in gas turbines, effusion cooling of the blades is an efficient way to alleviate the thermal and shear strain they sustain while increasing the temperature in the chamber.  A large-scale low-velocity experiment is carried out in the 3 x 1.5 x 20m3 test section of our closed-loop 10x5 wind-tunnel facility – Department of Aeronautics, Imperial College London. The scaled-up effusion device consists of a coolant-supplied settling chamber located directly underneath a perforated thick plate replacing a portion of the floor of the wind-tunnel. The effusion plate is pierced by a staggered grid of inclined D=16mm-diameter holes with a pitch of 5D. This set-up is placed in a turbulent boundary layer, tripped and developing over 15meters.  Three cases: a) no effusion, null flow rate coming out of the chamber; b) effusion without cooling, atmospheric air is supplied to the chamber; c) effusion cooling is supplied by a carbon dioxide cylinder; are investigated to let us identify independently the effects of holes-induced roughness (a), jet-injected momentum (b), and negative heat flux (c) on the flow dynamics. Hot-wire measurements provide velocity profiles at various locations throughout the effusion plate.