Energy Balance in the Pump Inducer with Taking Backflows into Account

Abstract

In elaborating the design of axial flow, screw, and centrifugal pumps, there is a need to know the moment at which backflow at the impeller inlet and flow at its outlet emerge, and also the effect these flows have on the pump power performance characteristics. By using advanced modeling techniques, it is possible to estimate the integral power performance characteristics of turbine machinery; however, they are not applicable for drawing up the balance of losses in an impeller. The article presents two new techniques that can be used to draw up an energy balance in axial flow impellers: a modified S.S. Rudnev technique for the energy balance in an inducer and a procedure for processing the results of numerical computer simulation in the ANSYS CFX software with dividing the flows into active, reverse, and back flow in the inducer at the pump inlet and at its outlet. A comparison is carried out with the procedures for calculating the theoretical head proposed by other authors, and a good qualitative agreement of the calculation results obtained using them is shown. By dividing the flows into an active, reverse, and back flow, we were able to determine the change in their cross-section areas, specific energies, and theoretical heads in the inducer on the entire Q-H curve. For the inducer with a straight leading edge (without trimming) and without taking the clearance into account, the active, reverse, and back flow cross-section patterns near the leading edge are presented. It can be seen on these patterns that backflows emerge earlier than they start to affect significantly the main flow parameters. It is shown that the active flow diameters and cross-section areas vary essentially at different distances from the leading edge. The flow pattern immediately at the leading edge differs from an axially symmetrical one.