Flow Instability Transferability Characteristics within a Reversible Pump Turbine (RPT) under Large Guide Vane Opening (GVO)

TL;DR

This study investigates flow instability transfer within a reversible pump turbine under large guide vane openings, revealing how flow pulsations propagate and are affected by runner blade number and operating conditions.

Contribution

It provides new insights into the transfer characteristics of flow instabilities in RPTs and how they depend on runner blade number and operating conditions, supported by CFD simulations.

Findings

Flow pulsation amplitudes increase as runner blade number decreases.

Flow instability propagates from turbine to other zones, influenced by operating conditions.

Flow pulsation levels vary with operating zones and runner blade configurations.

Abstract

Reversible pump turbines are praised for their operational flexibility leading to their recent wide adoption within pumped storage hydropower plants. However, frequently imposed off-design operating conditions in these plants give rise to large flow instability within RPT flow zones, where the vaneless space (VS) between the runner and guide vanes is claimed to be the base. Recent studies have pointed out the possibility of these instabilities stretching to other flow zones causing more losses and subsequent machine operational performance degradation. This study therefore intends to investigate the VS flow instability, its propagation characteristics, and the effect of machine influx and runner blade number on the same. CFD-backed simulations are conducted on ten flow conditions spanning from turbine zone through runaway vicinities to turbine brake (OC1 to OC15), using three runner models with different blades (7BL, 8BL, and 9BL). While VS pressure pulsation amplitudes increased with runner blades number decrease, the continuously decreasing flow led to gradual VS pressure pulsation level drop within the Turbine zone before increasing to Runaway and dropping back to deep turbine brake zone. The effect of the same parameters on the transmission mode to VS upstream flow zones is more remarkable than the downstream flow zones.