Nonaxisymmetric Study of Tip Leakage Flow in a Centrifugal Compressor With a Volute During Stall Process

Abstract

Tip leakage flow (TLF) patterns, which affect compressor performance, are closely related to compressor stability. To date, minimal attention has been given to circumferential nonuniformity of the TLF in a centrifugal compressor with a nonaxisymmetric volute structure. In this study, the circumferential difference of the TLF in a centrifugal compressor with a volute during the stall process is analyzed. The circumferential nonuniformity of tip leakage vortex (TLV) trajectories, loading distribution near the tip, and distance between the TLV core and the leading edge (LE) of splitter blades were also investigated. It is shown that in the circumferential direction, there are two peaks associated with the angle (α) between the TLV trajectory of the seven main blades and the axial direction. As the stall process progresses, the blade whose LE is affected by the high static pressure band (PP) induced by the volute tongue (VT) loses its work capacity first and the α difference between this blade and the other blades increases. In addition, the tip loading and TLF velocity of the blade whose LE is affected by the high static pressure band induced by the VT are at a minimum, and the flow loss in the tip clearance is higher. There is a phenomenon of the TLV breakdown. When the blade trailing edge (TE) is located in the low static pressure region, TLV streamlines appear as a significant turn at the breakdown point. However, the TLV streamlines at other circumferential positions do not exhibit this phenomenon.

Formation mechanism of static pressure circumferential double-peak distribution in a centrifugal compressor under the action of downstream boundary

“…The static pressure circumferential double-peak distribution also leads to significant differences in the TLF losses of different blades. The results of the references 28,29 showed that the TLF loss of the blade affected by HP1 is always the largest at any instance. With the development of the stall process, the TLF loss of the blade affected by HP2 gradually increases until it is very close to that affected by HP1.…”

“…27 A larger a indicates that the compressor is closer to the stall. The studies 28,29 showed that for a centrifugal compressor, the values of a at different circumferential positions are different, and there are two peaks in the circumferential direction, which corresponds to the circumferential position of the impeller inlet affected by the two high static pressure bands HP1 and HP2. The static pressure circumferential double-peak distribution also leads to significant differences in the TLF losses of different blades.…”

Evolution of unsteady vortex structures and rotating stall cells in a centrifugal compressor with vaneless diffuser

“…The intense secondary flow in the impeller also affects the rotating stall in the diffusor by causing circumferential distortion of its inlet flow, resulting in the hub-corner separation on diffusor vanes (Marsan et al, 2015). The circumferential non-uniformity for most centrifugal compressors is caused by volute governs the evolution of the rotating stall cells (Niu et al, 2020;Yang et al, 2019). The generation and disappearance process of rotating stall cells are observed due to the pressure distortion along the circumferential direction in a vaneless diffuser.…”