US Patent 7374401 Bell-shaped fan cooling holes for turbine airfoil

A turbine airfoil a plurality of cooling holes formed in the external surface of the airfoil in fluid communication with a cooling circuit. The cooling holes have a metering section and a diffuser section opening to the external surface of the airfoil. The diffuser section has top, bottom and opposed side walls, where at least the opposed side walls and one or the other of the top and bottom walls of the diffuser section have a downstream diverging, bell-shaped configuration for achieving a flow of the cooling film from the cooling circuit with enhanced spread, enhanced attachment and less turbulence to a downstream surface of the airfoil local to each respective cooling hole.