Parametric optimization of a hydraulic turbine stay vane considering fluid structure interactions
CHALLENGE - Vibrations in hydraulic turbines may arise due to an inappropriate design of components such as stay vanes. The purpose of the study is the optimization of the stay vane profile of a Francis turbine. It is found that the inadequate geometry of the profile leads to dynamic problems (vibration) related to the phenomenon of vortex shedding.
SOLUTION - To obtain the natural frequencies in water, the software ANSYS Mechanical is applied by performing a modal analysis that includes the effects of surrounding fluid in the structure. Calculated resonance frequencies are compared with experimental data. Computational Fluid Dynamics (CFD) analysis is performed for the optimized result to verify its fluid-structure behavior and to make a comparison between original and optimized structural displacements. The optimization method developed is able to eliminate resonance and to avoid excessive vibrations with just a few simple modifications in the original profile, as indicated by CFD simulations.
BENEFITS - The software modeFRONTIER runs the optimization process and chooses the best geometry parameters to avoid natural frequencies in water in order to be close to those estimated for the vortex shedding. The simulations gave results with minimal deviations with respect to experimental and analytical methods (approximately 5%). modeFRONTIER offers several optimal solutions, although the best choice depends primarily on the conditions the turbine operates. Values chosen for the parameters are (see figure above): c1 = 400 mm, c2 = 8 mm and c3 = 49 mm.