Investigation on the Stall Inception Circumferential Position and Stall Process Behavior in a Centrifugal Compressor With Volute

Abstract

The present paper numerically and experimentally investigates the stall inception mechanisms in a centrifugal compressor with volute. Current studies about stall inception pay more attention on the axial compressors than the centrifugal compressors; especially, the circumferential position of stall inception onset and the stall process in the centrifugal compressor with asymmetric volute structure have not been studied sufficiently yet. In this work, the compressor performance experiment was conducted and the casing wall static pressure distributions were obtained by seventy-two static pressure sensors firstly. Then, the full annular unsteady simulations were carried out at different stable operating points, and the time-averaged static pressure distributions were compared with the experimental results. Finally, the stall process of the compressor was investigated by unsteady simulations in detail. Results show that the stall inception onset is determined by the impeller leading edge spillage flow, and the occurrence time of trailing edge backflow is prior to the leading edge spillage. The non-uniform static pressure circumferential distribution at impeller outlet induced by volute tongue causes the two stall inception regions locating at certain circumferential positions, which are 120° and 300° circumferential positions at impeller leading edge, corresponding to the circumferential static pressure peak and bulge regions at impeller outlet, respectively. In detail, at rotor revolution 2.86, a small disturbance that the incoming/tip clearance flow interface is perpendicular to axial direction occurs at 120° position, but this disturbance did not cause the compressor stall. Then at revolution 7, the first stall inception zone (spillage region) occurs at 120° position, causing the compressor stall with positive pressure ratio performance. At approximately revolution 23, the second stall inception zone occurs at about 300° position; however, both the intensity and size of this stall inception zone are smaller than those of the first stall inception zone. These two stall inception zones are not moving along circumferential direction because the stall inception circumferential position is dominated by the impeller outlet static pressure distribution. Even that, the obvious low frequency signals appear after the spillage crossing two blade leading edges; because at this moment, the spillage vortex caused by the tip leakage flow begins to shed. However, due to the asymmetric structure limitation, this vortex cannot move across full annular. Furthermore, the spillage vortexes cause the local low static pressure zone ahead of blade leading edge in the centrifugal compressor with volute, suggesting that the spillage can be predicted by the steady casing wall static pressure measuring. The development of blockage zones at impeller leading edge is also investigated quantitatively by analyzing the stall blockage effect.

Influence of vaned diffuser on the potential effect of volute and stall inception of centrifugal compressor

“…The unsteady calculation of the stall development process was conducted to further ascertain the initial circumferential position and the development of the stall. The calculation method is the same as that in Zhang et al 42 Figure 10 demonstrates the time–space entropy contours at the 96% span of the impeller inlet plane ( x / c =−0.04 in Figure 1(a)). The abscissa is the circumferential position, and the ordinate is the rotor revolution.…”

Investigation of Stall Inception Behavior in a Centrifugal Compressor with Bent Pipe/Volute Coupling Effect

“…1, the volute tongue locates at a circumferential position of 55°. According to studies of the internal flow field at near stall condition in the compressor [24], the static pressure peak region (PP) and the static pressure bulge region (PB) at the diffuser outlet will occur near the volute tongue, locating at almost the opposite circumferential positions. This leads to two pressure waves propagating in the opposite direction from the upstream flow field, and consequently these two high-pressure regions locate at 120°and 300°circumferential positions at the impeller inlet, respectively.…”

“…Figure 3 explains the reason for the selection of installation angels of 120°and 300°for M1 and M2. References [24,31] investigated the casing static pressure distribution and stall behaviors of this Fig. 2 Total pressure distribution at 98% span and static pressure contour at bent pipe outlet for two bent pipe models at 80 krpm and near stall operation condition.…”

“…The results showed that the volute tongue induces the stall inception and determines the circumferential position of the stall inception at the centrifugal compressor inlet. Zhang et al [24] also investigated the stall inception circumferential position and stall process behavior in a centrifugal compressor with volute. The results indicated that in a centrifugal compressor with volute and vaneless diffuser, the stall inception occurs at the impeller inlet and is dominated by LE spillage.…”

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 affects the circumferential position of the stall inception of the compressor. The studies 30,31 determined that the stall region is first produced at the circumferential position affected by HP1 at the impeller inlet. With the development of the stall process, a second stall region is generated in the impeller inlet region which is affected by HP2.…”