Abstract: A radial compressor includes an impeller which is rotatively driven, axially introduces air taken in through an air inlet passage formed in a housing, pressurizes the introduced air, and discharges the pressurized air in a radial direction, wherein an annular concave groove is formed in a peripheral wall of the air inlet passage of the housing, a rear end portion of an opening of the annular concave groove, which rear end portion meets the housing peripheral wall, is provided in the vicinity of a blade front end surface of the impeller, and the rear end portion of the opening of the annular concave groove is formed such that an axial projecting amount X thereof relative to the blade front end surface of the impeller is set to ?1T?X?1.5T (where T denotes the thickness of the distal portion of a blade).

Abstract: A radial compressor is capable of preventing the occurrence of separation caused by a flow which goes beyond the front end of a blade and turns onto a negative pressure plane from a pressure plane, thereby reducing a surging flow rate to a smaller flow rate. The radial compressor includes an impeller which is rotatively driven, axially introduces air taken in through an air inlet passage formed in a housing, pressurizes the introduced air, and discharges the pressurized air in a radial direction, wherein an annular concave groove is formed in a peripheral wall of the air inlet passage of the housing, a rear end portion of an opening of the annular concave groove, which rear end portion meets the housing peripheral wall, is provided in the vicinity of a blade front end surface of the impeller, and the rear end portion of the opening of the annular concave groove is formed such that an axial projecting amount X thereof relative to the blade front end surface of the impeller is set to ?1T?X?1.

Abstract: There is provided a centrifugal compressor having a diffuser structure in which airflow is unlikely to separate from a hub side wall surface on a hub side wall surface downstream side within a diffuser passage. In a centrifugal compressor provided with a diffuser passage 15 for recovering static pressure by slowing down discharged air from an outer circumferential end of an impeller that rotates within a housing 11, a hub side wall surface 15b of the diffuser passage 15 is provided with an inclined plane 20 that approaches toward a shroud side, in a position on a downstream side of a portion parallel with a normal line direction of a section surface of an impeller exit.