On the flow-induced pulsating forces during load reduction of a Kaplan turbine model

Paper in proceeding, 2025

Intermittent renewable energy sources have become a significant part of the electric grid in the last few decades. With their implementation into the energy system and varying electricity demands from the market, certain challenges in maintaining a stable electric grid have arisen. Hydropower here finds an important role in the stabilisation of the grid with its possibilities to regulate frequency and power. However, this causes hydropower to operate in transient modes more frequently. Consequentially, more studies are necessary in order to safely operate the turbines during transients, to plan maintenance, and to predict the lifetime of the hydropower plants and the costs associated with new operating circumstances. There has been an extensive series of studies on transient operation of Francis turbines and pump turbines in recent years. However, transient operation of Kaplan turbines needs more in-depth studies. Therefore, the present work is focusing on the formation of oscillating flow structures and the evolution of the resulting flow-induced forces during load reduction of the U9-400 Kaplan turbine model. The study of the flow field is performed using the OpenFOAM open-source CFD code. The flow-induced horizontal and axial forces, and consequential bending moments and torque acting on the runner are analysed together with the flow structures forming in the draft tube at the best efficiency point (BEP) and at part load (PL).