| Summary: | Laser velocimetry measurements were taken in a double volute/single discharge centrifugal pump (0.60 specific speed, 1583
US units) with symmetrical volute halves. Blade-to-blade radial and tangential velocity profiles at the impeller exit are
presented and compared to data for a similar single volute pump. Flow rates ranged from 40% of design flow to the design
point. The blade-to-blade profiles were more uniform than for the single volute pump. Also, the average circumferential
variations for the double volute pump were more symmetric than for the single volute pump. For the double volute geometry
measurements indicate that radial inward flow (recirculation) was only present for flow rates below 60% of design flow,
compared to 80% of design flow for the single volute pump. Velocity data was also used to determine volute losses, slip
factor, and momentum contributions to the impeller radial forces. Volute losses were quantified and shown to increase for
flow rates below 80% of design flow and were approximately 10% of the developed head at 40% flow. The efficiency in
the double volute compared to the single volute shows decreased performance for flows above 55% of design flow, which
is attributed to increased boundary layer friction; at low flow rates increased performance is ascribed to better control over
the recirculation regions. Slip factors were symmetric around the volute but were lower than for a single volute pump.
Finally, momentum contributions to the total impeller radial load were shown to be maximum at the design point,
contributing 40% of the force developed by the pressure distribution; the significance diminished at lower flow rates and
the contribution was negligible at 40% of the design flow.
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