Loss analysis of a mix-flow turbine with nozzled twin-entry volute at different admissions

Abstract

This paper investigates performance and loss mechanism of a nozzled twin-entry mix-flow turbine at different admissions. Two sets of partial admissions and unequal admissions are analysed via experimentally validated numerical method. Results show that discrepancies of turbine efficiency between symmetrical unequal admissions (swopping inlet pressure on two entries) increase when unequal admissions approach to partial admissions, although their swallowing capacity is similar. Loss breakdown of turbine shows that loss is higher in nozzle but lower in rotor when the majority of flow is fed from upper part of the component (near shroud). Opposite phenomenon happens when the majority is fed from lower part (near hub). The reason for loss characteristic of nozzle is front-sweep configuration of the nozzle vane which results in evident flow separation when the flow is fed near the shroud. The reason for loss characteristic of rotor is the tornado-shaped vortex when the flow is fed from the hub. The tornado vortex is initiated by large incidence angle near hub and developed by the combination of Coriolis force, pressure gradient and centrifugal force. The study unveils loss mechanism among different admissions for a twin-entry turbine, which may enlighten the design methodology of the turbine with twin-entry volute.