Flow Characteristics of Preliminary Shutdown and Startup Sequences for a Model Counter-Rotating Pump-Turbine

Abstract

Pumped Hydropower Storage (PHS) is the maturest and most economically viable technology for storing energy and regulating the electrical grid on a large scale. Due to the growing amount of intermittent renewable energy sources, the necessity of maintaining grid stability increases. Most PHS facilities today require a geographical topology with large differences in elevation. The ALPHEUS H2020 EU project has the aim to develop PHS for flat geographical topologies. The present study was concerned with the initial design of a low-head model counter-rotating pump-turbine. The machine was numerically analysed during the shutdown and startup sequences using computational fluid dynamics. The rotational speed of the individual runners was decreased from the design point to stand-still and increased back to the design point, in both pump and turbine modes. As the rotational speeds were close to zero, the flow field was chaotic, and a large flow separation occurred by the blades of the runners. Rapid load variations on the runner blades and reverse flow were encountered in pump mode as the machine lost the ability to produce head. The loads were less severe in the turbine mode sequence. Frequency analyses revealed that the blade passing frequencies and their linear combinations yielded the strongest pulsations in the system.

System model development and numerical simulation of low-head pumped hydro storage

“…The comparison is based on the results of the high-fidelity model. The methodology and boundaries used for the CFD simulations are described in further detail by Fahlbeck et al (2021) and Fahlbeck et al (2022a).…”

Evaluation of startup time for a model contra-rotating pump-turbine in pump-mode

“…With the current design, the torque of the bevel gears is not to exceed 250 N•m according to the test facility at TU Braunschweig. Our earlier studies of a similar CRPT showed that large force and torque spikes are to be expected during the startup procedure in pump-mode if not handled with care [13]. These torque spikes can easily exceed the torque at the final operating point and must thus be limited.…”

“…Many of these studies lack an analysis of how the CRPT behaves at time-varying load conditions and mode switching between pump and turbine. Our recent studies show that the runners of the CRPT can experience rapid and large load variations during shutdown and startup procedures in pump-mode, where the startup seems to be the most crucial [13].…”

A new start-up law of pump turbines with misaligned guide vane devices

“…Chen et al 9 studied the variation process of pulsating pressure in runner area during start-up process based on 1D-3D coupling models. Fahlbeck et al 10 analyzed the flow characteristics under emergency shutdown and start-up condition. Liu 11 and Sabri et al 12 proposed that flow separation may occur at the runner blades under the case of no-load instability.…”