Extended Phase A-2, Large Cavitation Channel, Davld Taylor Naval Ship Research and Development Center

Abstract

It was suggested that a mild contraction located immediately upstream of the pump may improve the quality of flow which is expected to be quite nonuniform coming from the diffuser and the first and second elbow. To investigate the effect of the contraction ratio, the AROl computer model previously used in the Phase A-2 studies for the Large Cavitation Channel (LCC) main contraction design was applied to the pump contraction. As shown in Fig. 1, the contraction is assumed to be 5.563 m long and of circular cross section. Area contraction ratios of 0, 10, 20 and 30 percent were used. There is a fixed shaft of constant diameter along the centerline of the contraction. Two different shaft diameters, 0.508 m and · 1.016 m, were used based on information available at the time the study was conducted~ Initially, a fifth order polynomial was used for the contraction profile. The profile was later changed to a straight line because the contraction is so mild that the flow is not significantly affected by the boundary shape. Due to symmetry about the vertical plane, only half of the flow region was modeled. Different types of nonuniform inflow velocity profiles were studied. A total of 46 modeling runs covering various geometrical and flow conditions as well as different modeling parameters were made.