Abstract
This work presents the assessment of the mean flow field and low frequency disturbances in the stay vane channel of a model pump turbine using transient numerical simulations and LDV-based measurements. The focus is laid on transient CFD simulations of characteristic flow states in the stay vane channel when operating at off-design conditions in pump mode. Experimental and numerical investigations obtained a shifting velocity distribution between the shroud and hub of the distributor when continuously increasing the discharge in the part-load range. Simulations captured the occurrence of this changing flow state in the stay vane channel reasonably well. A further increase of the discharge showed a uniformly redistributed mean flow of both hub and shroud side. Monitoring points and integral quantities from measurements and transient simulations were used to interpret the development of transient flow patterns in the stay vane channel at the operating point of strongest asymmetrical flow. During simulation and measurement, a dominant rotating stall inception was observed near the design flow of the pump turbine. At this point where the stall becomes severe, a high level of correlation between the signals of the upper and lower stalled flow in the stay vane channel was calculated. Further simulations for different guide vane positions predicted a strong influence of the guide vane position on the structure of rotating stall.
Highlights
1 Introduction Increasing the operational flexibility of a pumped storage power plant often involves an extension of the continuous operating range of the pump turbine
Mesquita and Ciocan [1] are one of the few authors, who studied the flow in the stay vane channel of a pump turbine focusing on the flow between guide vanes and stay vanes
Close to the design point, the bulk velocity in the stay vane channel was found to be deflected towards the shroud where during deeper part-load operation the opposite was observed
Summary
Increasing the operational flexibility of a pumped storage power plant often involves an extension of the continuous operating range of the pump turbine. Large head variations are mostly associated with a wide off-design operating range. This makes it necessary to ensure off-design operating characteristics with low fluid dynamical effects at a high degree of reliability. During pump mode, part-load flow conditions can cause periodically unsteady flow patterns in the distributor section of the pump turbine. The occurrence of such unsteady flow phenomena upstream of the runner like stalling flow or Rotor-Stator-Interaction were investigated by many authors in the past. Mesquita and Ciocan [1] are one of the few authors, who studied the flow in the stay vane channel of a pump turbine focusing on the flow between guide vanes and stay vanes
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