7 - Mixed-flow and radial turbomachines

Abstract

This chapter deals with mixed-flow and radial turbomachines. The centrifugal compressor presents two inconvenient geometrical features. Firstly, the exit diameter must be much greater than the inlet diameter to obtain the centrifugal effect and consequent high head rise. Secondly, the flow path is turned radially outwards, delivering the air unhelpfully in the radial direction and requiring an exit volute. The axial compressor, on the other hand, while presenting the expense of its many blade rows, is geometrically ideally suited to the general flow requirements of a modern aircraft gas turbine engine that comprises an axial turbine and an axial bypass fan, in addition to the multi-stage axial compressor. For more general applications, fans fall into the three categories—namely, axial, mixed-flow, and radial.