Study on passive suppression method of rotating stall in mixed-flow pump: Using different impeller rim structures

Tip leakage flow (TLF) is not only an important factor causing hydraulic loss in mixed-flow pump, but also one of the inceptions of rotating stall. At present, limiting the stall of rotating machinery by restraining the TLF has gradually become a research hotspot of rotating machinery. However, in the field of mixed-flow pump, it is still in the initial stage of exploration. With the development of hydraulic machinery towards large-scale and high-speed, it is necessary to study its rotating stall suppression methods and expand its efficient operation range. Therefore, based on the idea of passive suppression of rotating stall, four new impeller rim structures are proposed in this study to optimize the performance of mixed-flow pump and to suppress or delay the occurrence of stall. The research results show that the geometric structure of the rim clearance has a significant impact on the energy performance of the mixed-flow pump, Bulge_Tip structure and Double_Rib_Tip structure make the critical stall and deep stall operating points shift to the low flow rate operating points, which improves the “saddle area” performance of the mixed-flow pump to a certain extent. However, there are two stall segments in the performance curve of Groove_Tip and Single_Rib_Tip structures, which worsens the pump performance in the “saddle area”. From the analysis of flow mechanism, it can be seen that Bulge_Tip structure and Double_Rib_Tip structure can restrain the loss of turbulent kinetic energy in the gap under stall condition to a certain extent, and limit the position and strength of unsteady secondary vortex (SV) structure at the impeller outlet, so as to shorten the stall range of mixed-flow pump without deteriorating the stall flow field in the impeller. Therefore, Bulge_Tip structure and Double_Rib_Tip structure has a light application prospect in stall suppression of hydraulic machinery.