Compressor shroud reverse bleed holes

A gas turbine engine comprising:

• a compressor section, a combustor and a turbine section, in serial flow communication;
• and
• at least one of the compressor section and the turbine section including:
• an axial rotor having a hub defining a central axis of rotation and a plurality of blades radially extending from the hub to project into an annular gas flow passage, each of said blades having a remote blade tip and a leading edge defined between opposed pressure and suction surfaces of the blades, said rotor being rotatable about said axis of rotation;
• a shroud circumferentially surrounding the rotor and having a radially inner surface adjacent to the blade tips, the inner surface of the shroud facing said annular gas flow passage;
• and
• a plurality of bleed holes extending through said shroud adjacent said blade tips, the bleed holes providing gas flow communication between said annular gas flow passage and a region outside the shroud, each of said bleed holes having an inlet end disposed in the radially inner surface of the shroud adjacent the blade tips to communicate with the annular gas flow passage, each of said bleed holes having an outlet end disposed in a radially outer surface of the shroud, bleed air removed from the annular gas flow passage by the bleed holes flowing in a bleed flow direction from the inlet end to the outlet end of each of the bleed holes, the outlet end of each of said bleed holes being located circumferentially upstream of the inlet end thereof, and the bleed flow direction at the radially inner surface of the shroud has a circumferential component that is opposite to a direction of rotation of the rotor.

A method of bleeding tip leakage flow from a gas turbine engine compressor comprising:

• providing a rotor rotatable about an axis of rotation within an outer shroud surrounding said rotor, the rotor having a plurality of radially projecting blades extending into an annular gas flow passage of the compressor, the annular gas flow passage being radially enclosed by an inner surface of the outer shroud, each of said blades having a remote blade tip and a leading edge defined between opposed pressure and suction surfaces, the inner surface of the shroud being adjacent to the blade tips and facing said annular gas flow passage;
• rotating said rotor to generate a main compressor flow within the annular gas flow passage in a first rotational direction corresponding to a direction of rotation of the rotor, a tip leakage flow being formed between the blade tips and the inner surface of the shroud, the tip leakage flow being in a direction opposite to the direction of rotation of the rotor;
• and
• bleeding off at least a portion of the tip leakage flow to a region outside the shroud using a plurality of circumferentially angled bleed holes extending through said shroud adjacent said blade tips, each of said bleed holes being disposed at an orientation at least partially aligned with the direction of the tip leakage flow, and the bleed holes being circumferentially angled such that a bleed flow direction at the inner surface of the shroud has a circumferential component that is opposite to a direction of rotation of the rotor.