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Flow in a Radial Turbine Under Equal and Partial Admission Conditions
Published March 19, 1991 by Institution of Mechanical Engineers in United Kingdom
A twin-entry radial inflow turbine with vaneless stator was tested at equal admission and a full range of partial admission conditions from zero to maximum flow in each entry. Measurements were made of the turbine performance at these conditions, and in addition the flow velocities and angles were measured at stations immediately upstream and a short distance downstream of the rotor. The best efficiency was found to occur, not at equal admission but when the ratio of the mass flows in the two inlets was about 0.6 (biased towards the rotor shroud). Otherwise there was a significant loss of performance at partial admission conditions. The fluid velocities at inlet to the rotor were also found to vary markedly across the blade span at the ratio of mass flows in the two entries were changed. At partial admission significant spanwise components of velocity were detected. By contrast, the flowfield in the rotor exit was relatively little affected by partial admission. The evidence of the flowfield measurements strongly suggests that the changes in performance at partial admission are linked to spanwise variations in rotor incidence angle and spanwise velocity components at inlet, via the secondary flow in the inlet region of the blade passage. This indicates changes to the volute which may improve the partial admission performance.