This paper investigated the unsteady fluctuation of inducer recirculation derived from diffuser stall which occurs near surge condition. The investigation was conducted using both experiment and unsteady numerical simulation.

Inducer recirculation is well known that the recirculation occurs near surge occurrence flow rate such as the flow rate which has a positive slope of the performance curve and the recirculation extends to the upstream of the impeller inlet when decreasing the flow rate more. However there are few papers investigating the unsteady phenomena of the recirculation in spite of the surge is the unsteady phenomena. In addition, understanding for the recirculation phenomena is essential to expand the operation range to the lower flow rate for centrifugal turbomachinery. For this reason we investigated the unsteady oscillation phenomena of the inducer recirculation.

A single-stage centrifugal blower with maximum pressure rise ratio of 1.2 was investigated and the flow rates near surge occurrence were focused on. This blower was equipped with an open type centrifugal impeller, vane-less diffuser, and scroll casing. The blower performance and pressure time-history data were obtained by the experiment. Unsteady simulations using Large Eddy Simulation (LES) were also conducted to investigate the flow field in the blower for each flow rate.

The performance curve obtained by the measurement showed that the positive slope of the pressure rise at the lower flow rate was due to the impeller stall and the inducer recirculation extended upstream of the suction pipe near at the slope of the curve was flat. The LES analysis could captured the trend of this pressure rise characteristics. This inducer recirculation had two typical fluctuation peaks, one was the 20% of rotation frequency and the other was 95%. The LES result indicated that the stall cell at impeller inlet propagated circumferential direction and swirled at almost the same frequency as the impeller rotation. In addition, the fluctuation at the diffuser derived from the diffuser rotating stall propagated to the suction pipe.


Fluctuation of Inducer Recirculation Stemming From Diffuser Stall in Centrifugal Turbomachinery Near Surge Condition

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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