An Attempt to Clarify Acceptable Pump-Throat Velocity-Distribution Criteria in Pump-Intake Model Studies

In order to ensure satisfactory full-scale pump performance, it is a common practice to conduct laboratory-scale hydraulic model studies for large circulating-water pump installations. Such water-intake models are generally constructed at an undistorted scale of about 1:8 to 1:12 and operated under Froude similarity laws. There are several final acceptance criteria to be met in the model tests, including types of free-surface and subsurface vortices, tolerable swirl angles, and allowable deviations of time-averaged point velocities from the time- and cross-section-averaged mean velocity. The last criterion on the pump-throat velocity distribution is not well defined, even in the Hydraulic Institute Standards. It is simply stated that time-averaged pump-throat velocities should be within 10% of the area-averaged velocity. Why 10%? Can we allow other percentages of deviations? Is it fair to treat point velocities measured at different parts of the pump-throat cross section equally? Or, should we use different criteria using point velocities weighted by local areas of the throat cross section? There are many such questions. This paper steps into this murky area of the velocity-acceptance criterion and shows some analyses based on the past model test results obtained at Iowa Institute of Hydraulic Research (IIHR), The University of Iowa.