It is known that the compression work of gases can be largely reduced by inter-stage cooling. Multistage radial compressors have been developed in the past with coolers integrated within the casing. Such a solution, however, is limited to medium volume flows of about 40 m3/s. For larger flows, a combination comprising an axial low pressure section with variable guide vanes for flow regulation, used as supercharger, followed by a multistage radial section with integrated coolers, has been developed. The major parameters governing this choice are presented. Aerodynamic tests on the axial and radial sections have been carried out with a special emphasis on the aerodynamic layout of the diffusor connecting the axial or the radial sections to the coolers. The tests have shown that a considerable amount of aerodynamic improvement could be obtained by a proper disposition of asymmetrical guide vanes dividing the total flow going to the coolers placed symmetrically on each side of the casing. Test results on the complete machine, regarding its aerodynamic characteristics and the noise level as well as its mechanical behavior, are given.

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