Simulation-based evaluation of the 3D fluid dynamics of a coolant lubricant in the narrow-closed cutting gap during circular sawing

A method for simulation-based analysis of the 3D fluid dynamics of a coolant lubricant in the saw tooth space is presented. The examination serves on the one hand to characterize the flow around the bounding surfaces of the narrow-closed cutting gap regarding the local flow conditions. On the other hand, the outflow behaviour of the coolant lubricant out of the narrow-closed cutting gap is analysed to get a deeper understanding of the cooling mechanism. Therefore, the model design is described considering the computational domain and the boundary conditions. Finally, an evaluation method for the local flow behaviour at different surfaces and the coolant lubricant outflow of the tooth space in the narrow-closed cutting gap is illustrated

Scale-Resolving Hybrid RANS-LES Simulation of a Model Kaplan Turbine on a 400-Million-Element Mesh

Double-regulated Kaplan turbines with adjustable guide vanes and runner blades offer a high degree of flexibility and good efficiency for a wide range of operating points. However, this also leads to a complex geometry and flow guidance with, for example, vortices of different sizes and strengths. The flow in a draft tube is especially challenging to simulate mainly due to flow phenomena, like swirl, separation and strong adverse pressure gradients, and a strong dependency on the upstream flow conditions. Standard simulation approaches with RANS turbulence models, a coarse mesh and large time step size often fail to correctly predict performance and can even lead to wrong tendencies in the overall behavior. To reveal occurring flow phenomena and physical effects, a scale-resolving hybrid RANS-LES simulation on a block structured mesh of about 400 million hexahedral elements of a double-regulated five-blade model Kaplan turbine is carried out. In this paper, first, the results of the ongoing simulation are presented. The major part of the simulation domain is running in LES mode and seems to be properly resolved. The validation of the simulation results with the experimental data shows mean deviations of less than 0.8% in the global results, i.e., total head and power, and a good visual agreement with the three-dimensional PIV measurements of the velocity in the cone and both diffuser channels of the draft tube. In particular, the trend of total head and the results for the draft tube differ significantly between the scale-resolving simulation and a standard RANS simulation. The standard RANS simulation exhibits a highly unsteady behavior of flow, which is not observed in the experiments or scale-resolving simulation

Strategic Research Agenda of the EERA Joint Programme Hydropower

The launch of a new EERA Joint Programme on Hydropower is good news for energy system in Europe and beyond. The clean energy transition is necessary, demanding and accelerating. Hydropower in Europe and worldwide represents a significant tool for achieving this change sustainably. Hydropower holds capabilities for energy supply, storage, and regulation that are unique. These characteristics are needed to deliver security of supply, stability in the grid, and for green growth. Increasing the flexibility of the hydropower fleet through innovation and modernisation is fundamental for these objectives. Hydropower has a lot to offer. It can provide water management capabilities, mitigating damage from flood and drought events; it will provide clean energy and available capacity for stable and secure supplies; it will balance intermittent production from solar and wind, and it is capable of storing energy, both in short and long-term horizons. Hydropower rates very well in comparison to other renewable electricity production sources, including storage: energy-payback ratio, life-cycle assessment, greenhouse-gas emissions, water footprint, and more. Adding to that, hydropower has the highest energy-conversion efficiency and longest operating life. Without research, demonstration and investment, none of these roles will be optimised for the future. Europe is instrumental in leading the way towards decarbonisation through competence building and innovation. And the Joint Programme on hydropower represents a renewed focus on new roles and priorities for hydropower; we can no longer rely only on the mature solutions and methods; we need to bring our existing knowledge further. What happens in a power plant that shall handle thirty starts and stops each day? How can we utilise rotating mass to provide instant regulation for the system? How will power peaking affect the watercourse, and how can we integrate water management solutions together with power production, recreation and navigation? New challenges present new opportunities, but also new needs for research and innovation. The Joint Programme on Hydropower in EERA comprises a large group of excellent and dedicated R&D-communities in Europe. Our joint eff orts will be a major hub for renewed research, supporting eff orts to modernise the European fleet and assist the rest of the world, where the largest potential for new hydropower development lies. My hopes and expectations for this initiative is that it will expand globally and be a platform for research on topics related to hydropower in a world-wide perspective. The need for this initiative is clear, and everyone involved should be very proud of the launch of this platform