抄録
In the present study, the effect of volute casing on the head/discharge characteristics with 2-step positive slope of a centrifugal pump has been investigated through calculating internal flow field. Based on the hypothesis of axisymmetric flow field, the numerical simulations on the incompressible turbulent flow have been carried out for partial-blade passages with periodic boundary conditions. As a model of the volute casing, a parallel diffuser or three volute casings with different configuration was prepared in the simulation. The result on each head/discharge characteristic curve has the same tendency as the experiment in the positive slope. At partial flow operation, the pumps with each model have the large backflow and recirculation regions in two locations, one of which is near the casing at the impeller inlet and the other near the central part of the diffuser. The scale of these regions varies steeply under two partial flow operation points as the discharge changes. The results show that the dominant factor of the positive slope is independents of the configuration of volute casing and exists in the upwind of volute casing.
