Motivation
With regard to the technical design of hydraulic turbomachines, computational fluid dynamics (CFD) is an important process of increasing importance. The goal is to quickly and efficiently design and simulate a turbomachine without expensive and costly testing equipment. The results obtained can be evaluated with regard to a wide variety of parameters and thus an optimized design can be found. Using an automated design system with built-in workflows supports the optimization process.
Design chain
The design of a turbine depends on the conditions at the place of installation. Due to these boundary conditions, a first model can be created with the help of analytical estimates and empirical values. In the design system, an existing variant can also be automatically remodeled. The integrated generation of the numerical grid for the simulation can save a considerable amount of time in the development process. The following simulation can be performed using different solvers.
In the following evaluation besides numerical methods also the Virtual Reality environment COVISE is used. By visualizing the geometry with the simulation results, the operator receives direct visual feedback and can thereby identify and intuitively adjust the parameters with optimization potential. For better illustration, an additional output in 3D is possible. At the High Performance Computing Center (HLRS), a 5-wall CAVE is available for this purpose.
This methodology can be used to optimize the various components of a turbine. Thus, for example, the flow around the blade and outflow into the draft tube can be optimized on the impeller by adjusting geometrical parameters. As a result, the efficiency is improved and prevents material from damage by avoiding cavitation phenomena. In addition, the design system can be operated without a graphical user interface to perform automatic optimizations. Variants are automatically generated, meshed, simulated and evaluated so that a machine is improved without manual effort.
Numerical simulation of hydraulic machinery
The numerical simulation of a turbine gives the pressure and velocity field inside the machine as a result. At previously defined points of the numerical grid, the unknowns are calculated and from this an overall course is approximated. A parameterization of the entire system consisting of guide vane, runner and draft tube results in many degrees of freedom. The relationship between degree of freedom and effect on the flow field or machine property is usually unknown. A sensitivity study or principal component analyses explores such relationships and is able to reduce the existing models.
The automated optimization and sensitivity analysis requires the calculation of a large number and very different geometric variants. A hybrid calculation grid consisting of tetrahedrons, hexahedrons and pyramids improves the robustness of the process. In terms of extensibility, the design system is programmed in C++ and is based on object-oriented paradigms. It mainly uses open source libraries for geometry generation, simulation, meshing and evaluation.
