Sediment erosion is one of the key challenges in hydraulic turbines from a design and maintenance perspective in Himalayas and Andes. Past research works have shown that the optimization of the Francis turbine runner blade shapes can decrease erosion by a significant amount.
This study conducted as a Master’s Thesis has taken the proposed designs from past works and conducted a CFD analysis on a single passage of a Francis runner blade to choose an optimized design in terms of erosion and efficiency. Structural analyses have been performed on the selected design through one-way and two-way FSI to compare the structural integrity of the designs.
Two types of cases have been considered in this thesis work to define the boundary condition of the structural model. In the first case, a runner blade is considered to have no in influence of the joint and other stiffer components. In the second case, a sector of the whole runner has been modeled with necessary boundary conditions. Both one-way and two-way FSI have been performed on the cases for the designs. Mesh independent studies have been performed for the designs, but only for the first case, whereas in the second case, a fine mesh has been used to make the analysis appropriate.
The loads have been imported into the structural domain from the fluid on the interfaces for one-wayFSI. In the case of two-way FSI, the Multi-Field Solver (MFX) supported by ANSYS has been used to solve the coupled field analysis. A fully coupled FSI in ANSYS works by writing an input file in the structural solver containing the information about the interfaces in the structural domain, which is imported in the fluid solver. The interaction between the two domains is defined in ANSYS-CFX,including the mesh deformation and solver setups.
The results have been post-processed in CFX-Post, where the results from both the fields are included. It has been found that the structural integrity of the optimized design is better than the reference design in terms of the maximum stress induced in the runner. The two-way FSI analysis has been found as an inevitable part of the numerical analysis.However, with the advancement of the computational capability in the future, there could be a great scope in the research field to carry out a fully-coupled transient simulation for the whole runner to get a more accurate solution.
Source: KTH
Author: Chitrakar, Sailesh