The influence of the vane diffuser head losses curve on the external characteristic of high specific speed pumps

Abstract

In the petroleum industry the production process is secured by the proper operation of water pumps. Their correct selection, operation and maintenance reflect in the energy efficiency of the whole process, thus, the stable H-Q curve, correlated with the highest efficiency, is required in the operation range of the unit. The article concerns the problem of the s-type instability creation on the example of a mixed-flow pump. For the analyzed pump, where the instability of the flow curve occurs in a normal operation range, the experimental characteristic curves were measured. Based on those curves the numerical model was created and verified. The essential novelty of the article reflects in the phenomenon of the head losses rise in the vane diffuser while decreasing the pump discharge, approaching its local minimum in the best point of the pump. This phenomenon was caused by the mutual cooperation of the impeller and diffuser, specially by the impact of the non-uniformed flow structure supplied to the diffusor on its hydraulic performance. Obtained results of the impeller-vane diffuser cooperation were compared in the numerical aspect with the diffuser operation supplied by the uniform flow profile. Such analysis allowed to indicate the reason for the instability creation, where quite flat characteristic of the impeller reference to the head losses curve of the diffuser leads to the creation of the deflection point in the H-Q curve. To extend the scope of the conducted numerical research of the head losses curve increase phenomenon in course of the flow reduction in the vane diffuser of the high specific speed pump the analyses were also performed for the axial pump.