Film cooling passages with curved corners

A cooled wall having an outer surface adapted to be exposed to a hot gas stream flowing in a downstream direction over said outer surface, and an inner surface adapted to define a portion of a coolant compartment for receiving coolant therein under pressure, a coolant passage within said wall, said passage having an outlet over which the hot gas flows in said downstream direction and including a metering section in series flow relation with a diffusing section, said diffusing section having an inlet and outlet, said metering section adapted to receive a flow of coolant from the coolant compartment and to control the rate of flow of coolant fluid through said passage, said diffusing section including an upstream surface spaced apart from and facing a downstream surface, said first and second surfaces being parallel to each other or diverging from each other toward said outer surface and intersecting said outer surface of said wall at a shallow angle to define said outlet of said coolant passage, said outer surface extending downstream of said passage outlet, said coolant passage being oriented to direct the flow of coolant from said passage outlet such that is has a component of velocity in the downstream direction and forms a film of coolant over said outer surface downstream of said passage outlet, said first surface forming an upstream edge of said passage outlet where it intersects with said outer wall and said second surface defining a downstream edge of said passage outlet where it intersects with said outer wall, said diffusing section including side surfaces facing each other, interconnecting said upstream and downstream surfaces and diverging from each other toward the outlet of said diffusing section, each of said side surfaces blending along substantially its full length with said downstream surface as a smooth curve having a diameter on the order of magnitude of the distance between said upstream and downstream surfaces at the location of said blending.