Patent ID: 7004722

Claim:
An axial flow compressor, comprising: a rotary hub; a plurality of rotor blades extending radially from said rotary hub; and an outer casing having an inner circumferential wall opposing tips of said rotor blades defining a small gap therebetween, wherein said inner circumferential wall of said outer casing opposing the tips of said rotor blades comprises, as seen in a longitudinal section, of a cylindrical large diameter section disposed in an upstream section and having a starting point located from a leading edge of the tips of said rotor blades, a cylindrical small diameter section having a smaller diameter than said large diameter section disposed in a downstream section, and an intermediate section having a diameter that monotonically decreases from an upstream end to a downstream end, in a continuous manner, the intermediate section being provided with a concave surface opposing said rotor blade tips as seen in a longitudinal section said concave surface comprises a curved surface extending smoothly from a start point located between a leading edge of the rotor blade (0% axial chord position) and a 30% axial chord position to an end point located between a 50% axial chord position and a 80% axial chord position, and a stagger angle α between tangential lines at the start and end points of the concave surface is within ±5 degrees of an angle given by the Prandtl-Meyer function.