Patent ID: 8220276

Claim:
A gas turbine axial flow compressor, comprising: a casing; a rotor hub rotatably borne in the casing; an axial flow compressor duct disposed between the casing and the rotor hub; at least one rotor, which is rotatable about a machine axis; at least one stator, the at least one rotor and at least one stator being positioned axially spaced from one another within the axial flow compressor duct; a bleed air tapping device having a plurality of recesses axially positioned in the casing both: outside of a bladed space of the at least one stator, and at least one of: before or behind a blade row of the at least one rotor or between two blade rows of two rotors; which recesses, in at least one circumferential area, are arranged circumferentially to each other, wherein each recess includes, in a circumferential direction, a circumferential leading edge and a circumferential trailing edge, each of which is situated at an identical angle (β E ) with a surface of the casing, this angle being calculated as per the following formula: β E = arc ⁢ ⁢ tan ⁡ ( ξ ⁢ ⁢ π ⁢ ⁢ r G 2 ⁡ ( 1 - v 2 ) A BLEED ⁢ tan ⁢ ⁢ BOA ) , where (ξ) is a dimensionless air quantity to be tapped, which derives from an extraction air flow m BLEED and a compressor air flow m COMPRESSOR and is calculated as follows: (ξ)= m BLEED /m COMPRESSOR . (r G ) is a casing radius at the circumferential leading edge, (r N ) is a hub radius, (ν) is a hub ratio at the circumferential leading edge, with (ν)=r N r G , (A BLEED ) is a total surface of all recesses of the circumferential area, and (BOA) is an identical angle of the circumferential leading edge and the circumferential trailing edge, relative to a straight line located parallel to the machine axis, with the angle (BOA) satisfying one of the following rules: a) if a stator vane exists upstream of the recess, the angle (BOA) ranges within ±10 degrees of a metal exit angle (MW STATOR ) of the stator vane in a range of 95 percent to 100 percent of the blade height of the stator, b) if a rotor blade exists upstream of the recess, the angle (BOA) is calculated from the metal exit angle (MW ROTOR ) of the rotor blade ±10 degrees in a range of 95 percent to 100 percent of the blade height of the rotor as per the following equation: BOA =arctan(2−tan MW ROTOR ) c) if no blade row exists upstream of the recess, the angle BOA is 0 degrees.