Air intake duct structure for centrifugal fluid machine

Abstract

An object is to provide an air intake duct structure for a centrifugal fluid machine, capable of swirling the fluid introduced into the impeller in the reverse direction to increase the pressure ratio when the flow rate is high and swirling the fluid in the forward direction to avoid a surging when the flow rate is low, as well as securing a wide operating range, without using mechanical means. The centrifugal fluid machineincludes an impellermounted to a rotation shaft and a housingfor housing the impeller. The air intake duct structureis for directing a fluid 'f' to a rotational centerof the impellerhoused in the housingvia an intake duct portionof the housingprotruding in an axial direction of the rotation shaft, the fluid 'f' flowing in a substantially orthogonal direction to a rotational axis line. The air intake duct structurecomprises an inflow partextending in the substantially orthogonal direction to the rotation axis lineand a transition partconnecting the inflow partand the intake duct portionof the housing. There is a virtual planeorthogonal to the rotational axis lineand passing through a flow path cross-section of the inflow part, where an intersectionof the virtual planeand the rotational axis lineis positioned within the transition part