Investigation of the Flow Conditions in a Centrifugal Pump

Abstract

Abstract This paper gives an account of an investigation recently carried out in the laboratory of the Technical University of Munich, into the flow conditions in the impeller of a centrifugal pump, the results of which may be summarized briefly as follows: (1) Practically all flow conditions for an actual fluid are fundamentally different from those theoretically derived for an ideal frictionless fluid. (2) The dead-water zones which form on the low-pressure sides of the blades undoubtedly cause a reduction in the angle at which the fluid leaves the blades from the actual blade angle. (3) The actual velocity distribution along circles concentric with the axis of rotation of the impeller is not the same as the supposed distribution computed on the basis that the fluid passages are completely filled with active flow. (4) The relative velocity along the high-pressure side of the blade should theoretically approach zero for relatively small reductions in the discharge below normal and with the fluid passages completely filled with active flow. Actually this velocity is greater than the theoretical value, and reverse flow along the pressure side of the blade does not take place even at small discharges. (5) In addition to (4), it was definitely proved that the flow at very small discharges is no longer stable. (6) The entrance flow may be assumed to be radial for all practical operating conditions. (7) The increase in the meridional velocity over the ordinary computed value alters the shape of the exit triangle considerably, which is of special importance in designing the guide-vane entrance angle.