Suction recirculation mitigation in a double-suction centrifugal pump

Abstract

Suction recirculation in centrifugal pumps operating at o˙-design conditions is an eventual reality for all centrifugal pumps. Various types of modifications to both the pump impeller and/or volute have been implemented in the past, with variable success. The successful implementation of the modifications is often counteracted by either an increase of Net Positive Suction Head Required (NP SHR), a narrowing of the band of recirculation-free operation and/or the need for intrusive casing modifications. This study aims to determine if a suitable suction recirculation mitigation method, that restricts the suction recirculation phenomenon while not exhibiting a noticeable increase in NP SHR, is possible by means of the implementation of a profiled bulkhead-ring. Suction recirculation can be described as the separation of the flow field and the presence of a separation cell in the suction half of the impeller between-vane cavity with a back-flow of fluid from impeller to suction volute. Two scenarios were investigated: the unmodified pump, and the modified pump geometry includ-ing the modified bulkhead-ring - simulated across the entire operating range. The flow charac-teristics of both cases were investigated after adequately verifying the numerical simulations and validating these results with analytical and certified experimental methods. The results of the study indicated that the modified bulkhead ring concept was partially e˙ective by successfully restricting the bulk back-flow of fluid from impeller to suction volute, however the separation point and recirculation cells remained largely una˙ected. In this particular instance, both the measured and simulated NP SHR showed a noticeable increase after the implementation of the modification. Although the results of this particular study do suggest that the installation of the particular rotating modification used in the current setup is not generally more practical when compared to more conventional methods, further development is needed in order to determine a more optimal ring geometry that would produce more favourable results.