Investigation of Skewed Slot Casing on Transonic Axial-Flow Fan Stage

In this paper, a highly loaded transonic fan stage, which was designed and tested by Wennerstrom in the 70's was selected to study the functions of skewed slot casing treatments. Three casings, each different in axial locations and slot directions, were designed and numerically studied by this research. Experience on optimum slot location and direction was summarized. The simulation was run by commercial CFD software Fine/Turbo. Un-steady simulations were performed on the casing treated rotors to depict the real nature of unsteadiness in a slotted casing. The rotor exit boundary conditions were set according to the parameters extracted from the stage simulation. With this condition, computational expense was much saved, and the attention was made solely focused on the slots and rotor interaction. Performance simulation at partial design speed (70% design speed) was also conducted. Unexpected performance improvement with the treated casing was observed at this speed. This unusual phenomenon was analyzed, with a corresponding explanation provided.