An experimental investigation was carried out to clarify unsteady flow fields with rotating stall cell, especially structure and behavior of stall cell, in a high specific-speed diagonal flow fan. As its specific-speed is very high for a diagonal flow fan, its pressure-flow rate curve tends to indicate unstable characteristics caused by rotating stall similar to axial flow fan. Although for an axial flow fan many researchers have investigated such the flow field, for a diagonal flow fan few study has been done. In this study, velocity fields at rotor inlet in a diagonal flow fan were measured by use of a single slant hot-wire probe. These data were processed by use of the “Double Phase-Locked Averaging”(DPLA) technique, i. e. phases of both the rotor blade and the stall cell were taken into account. The structure and behaviors of stall cell at rotor inlet were clarified for three dimensional velocity components, Vm, Vθ, and Vn.
