Partial flow separation in guide-vane region of large-capacity/low-head pumped hydro energy storage system with horizontal shaft

Abstract

The hydraulic performance of a large-capacity/low-head pumped hydro energy storage system is usually assumed to be consistent with that of its hydraulic model system, that is, the energy parameters and the inner flow fields conform to the conventional similarity law. However, this expected hydraulic consistency may not be realized in actual engineering projects. In a prototype system with horizontal shaft, head change and vibration enhancement have been observed, but the origin of this inconsistency is still unclear. This article investigates the inner flow characteristics in the guide-vane region of a prototype system with horizontal shaft in the optimal pump mode. A new phenomenon, partial flow separation, is discovered. The most intuitive feature of partial flow separation is that large-scale separation vortices in the guide-vane region are concentrated in the top passages of the antigravity part, while the bottom passages demonstrate good through-flow capacity. This is significantly different from the axisymmetric inner flow structures in the model system. Further in-depth analysis shows that this new phenomenon directly stems from the constant circumferential imbalance of inflow attack angles, and is further attributed to the blade loading polarization in the impeller region under pronounced gravity effects. More importantly, partial flow separation can adversely affect energy performance and operation stability, including the aggravation of energy loss in the guide-vane region and severe flow deviation in the outflow passage. Particular attention should be paid in the future to the design and operation of large-capacity/low-head pumped hydro energy storage systems with horizontal shaft.