The basic research question of the FFG project AxFeeder is to find out how distributor systems of Pelton turbines have to be designed in order to have similar flow conditions in the feed line and the injectors in all operating conditions and to achieve the best possible jet quality.

For this purpose, a comprehensive parameter study based on numerical flow simulations of potentially suitable hydraulics of distributor systems with axial inflow was conducted in a first project step. The findings of this parameter study will now be used to perform a detailed flow/vibration and structural mechanics analysis of the overall system. For this purpose, the project team will perform scale-resolving simulations on the Vienna Scientific Cluster (VSC) and, in parallel, design a laboratory test rig on which experimental investigations will be carried out.

Poster EN [PDF Download], opens a file in a new window

Especially when operating in pump-mode, part load flow in pump-turbines is still a challenging task since crucial flow regimes become apparent in the entire flow
domain. In deep part load, the occurrence of flow instabilities is evident. Flow phenomena like rotating stall in the guide vane or pre-rotating flow at the runner
inlet are mainly responsible for an improper blade load. Another consequence is oscillating flow upstream of the runner, which results in the so called "off-design"
operating conditions, see Figure. Existing modeling approaches and further developments of linear eddy-viscosity RANS models considering rotation effects are implemented into the CFD soft-ware and validated by means of generic flow problems. The two-equation turbulence model SST k-ω is primarily employed for sensitizing methods used for transient incompressible single- and two-phase flow simulation. Simulation results of pump-turbine flow are directly compared with experiments making the interpretation of results more reliable.
A practical two-phase study considers the performance break-up due to leading edge cavitation of the pump-turbine runner during low partial flow rates, as well as a direct comparison with test-rig measurements.

Within the last decade the rising amount of volatile sources of energy, such as solar and wind power, led to a falling price on the energy spot market. As a result , there are higher requirements in terms of grid stabilization efforts. Therefore operators of hydropower plants are using their machines to provide balancing energy to the electrical grid. However, this leads to significant worse operating conditions in off-design points as well as to a higher number of start-ups and shut-downs. Thereby, flow phenomena and mechanical structure resonance determine the runner lifetime. Based on the results of the previous project PSP-LowLoad, a further development of the fatigue analysis including prototype site measurements and numerical simulations was aspired. Furthermore, the detection of critical operating points by means of the monitoring systems was investigated. The results of the project have/will been published in several papers and presented at scientific conferences.