Cooled aerofoil for a gas turbine engine

A cooled aerofoil for a gas turbine engine configured to separate flows of cooling air to aerofoil surfaces having different external static pressures, the cooled aerofoil comprising:

• an aerofoil section having pressure and suction surfaces extending between inboard and outboard ends of the aerofoil section, the aerofoil section including:
• a first and a second internal passage configured to carry cooling air, the first and second internal passage being supplied with cooling air from respective and separate passage entrances, each passage entrance being located at either the inboard end or the outboard end of the aerofoil section;
• and
• a plurality of external holes in the external surface of the aerofoil section configured to receive cooling air from the internal passages, the external holes being arranged such that:
• (1) cooling air exiting from a first portion of the external holes contribute to a cooling film extending from the leading edge of the aerofoil section over the pressure surface and (2) cooling air exiting from a second portion of the external holes contribute to a cooling film extending from the leading edge over the suction surface, wherein
• the first portion of external holes receives cooling air from the first internal passage, the second portion of external holes receives cooling air from the second internal passage, and
• the second internal passage is a high pressure drop multi-pass passage or a highly flow-disrupted passage configured to reduce a coolant air pressure to the suction surface external holes such that the coolant air pressure matches the low static pressure of a hot gas at the suction surface to avoid disrupting the cooling film, wherein
• the second internal passage includes:
• (1) a fore section which extends towards the leading edge and (2) an aft section, the cooling air entering the aft section before the fore section, the flow direction of the cooling air in the aft section being predominantly radial, and the flow direction of the cooling air in the fore section being predominantly in aft-fore direction.