Effect of circumferential static pressure nonuniformity caused by volute on tip leakage flow in a centrifugal compressor

Abstract

For a centrifugal compressor with volute, the flow field is circumferentially nonuniform because of the volute asymmetrical structure and leads to a circumferential difference in the tip leakage flow. In this work, the compressor performance and the casing wall static pressure distribution are measured, and the results are compared with the time-averaged results of the unsteady calculation to verify the reliability of the simulation. The results show a relationship between the tip leakage vortex trajectory and the high static pressure region in the diffuser, based on which a prediction model is established for the reverse propagation of pressure waves caused by a volute tongue. Influenced by the volute asymmetric structure, the trajectory, shape, and strength of the tip leakage vortex at different circumferential positions differs significantly. The tip leakage vortex trajectory affected by the high static pressure is more inclined to a circumferential direction because the tip leakage flow velocity flowing out of the suction surface is reduced, and the tip leakage flow with low velocity is subjected to the high-pressure gradient in a passage. Moreover, the tip leakage vortex breakdown in different passages differs significantly. A tip leakage vortex core more inclined towards the streamwise direction is more likely to break down than a tip leakage vortex core inclined towards the circumferential direction because of the larger reverse pressure gradient.

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

“…Given the 60°b lade angle, the maximum angle between the TLV trajectory and axial direction is 82°for CVL at OP, and the compressor enters the stall. 33 However, the maximum angle between the TLV trajectory and axial direction is 79°for CVD, indicating that the CVD does not stall at OP.…”

“…The airflow instability occurred first for the blade passages with a larger reverse pressure gradient. The stall inception appeared at the circumferential position with a larger reverse pressure gradient induced by the VT. 30,32 Based on this, Fu et al 33 investigated the phase shift in the propagation of the pressure wave (PW) caused by the volute. They developed a computational method to determine the circumferential position of the impeller inlet affected by the VT.…”

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

“…To determine the formation path of the double-peak distribution, it is necessary to analyze the circumferential deflection behavior of the static pressure band. Previous studies 28,34,35 showed that the circumferential deflection of the static pressure band is caused by the combined action of the blade wrap angle and the impeller internal flow caused by the impeller rotation. Fu et al 28 deduced the formula of the deflection angle when the high static pressure induced by VT propagates reversely from the impeller outlet to the impeller inlet.…”

“…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.…”