Further numerical investigation of optimum structure of axial slot casing treatment on a two-stage transonic fan

This paper is another small step forward in NWPU (Northwestern Polytechnical University) long-standing research on improving axial slot casing treatment. The numerical investigation of the optimum structure of axial slot casing treatment is performed on a high rotating speed and high load two-stage transonic fan. Section 1 of the full paper explains our new ideas on optimizing the axial slot casing treatment; in particular, in addition to the original optimum structure, we propose three new structures, which we call structures No.1, No.2 and No.3. Section 2 briefs the numerical calculation method which we have been using. Section 3 presents numerically calculated results, given in Figs. 2 through 6 and Table 1, and their analysis, which show preliminarily that: (1) the three new casings have no capacity for extending the operating range of the fan under transonic condition, and this is consistent with the experimental and calculated results of the original casing; (2) the stall margin improvement is higher with the structures No. 2 and No. 3 of the new casing treatment than with the original casing treatment under subsonic condition; the mechanism of extending the stall margin under subsonic condition is explored with detailed analysis of flow-field in the fan as given in Figs. 4 through 6; the extension of the treated area of casing structure No.2 increases the ability of bleeding or blowing blade tip low energy flow mass, thus improving the flow capacity near tip passage; (3) because the structure No.3 uses the pressure difference better than structure No.2, its stall margin improvement is further increased with the accompanying improvement of the fan performance; the compressor efficiency is higher with No.3 casing treatment than with No.2 casing treatment as shown by the results in Fig.3.