Numerical analysis of inflow turbulence intensity impact on the stress and fatigue life of vertical axis hydrokinetic turbine

Abstract

The present study aims to analyze the effect of upstream turbulence intensity on the hydrodynamic and structural performance of the straight-blade vertical axis turbine. To achieve this, a one-way fluid structure interaction analysis is conducted within the ANSYS workbench environment. Initially, computational fluid dynamics (CFD) simulation is performed at different values of upstream velocity values. Additionally, the impact of upstream turbulence intensity is also analyzed. The CFD simulation results were validated against published experimental work. Once CFD simulation is performed then computed fluid loads are transferred to the ANSYS mechanical structural module. Finite element modeling is performed to compute the stresses and the fatigue life. The study reveals that increasing the upstream turbulence intensity from 5% to 20% leads to 8.6% improvement in the turbine's power performance. However, turbulence intensity also results in 35.6% increase in Von-Mises stresses produced within the designed turbine. However, even with this increase, the Von-Mises stresses remain below a critical threshold, measuring at 173.34 MPa when the upstream water velocity is 1.4 m/s, and the inflow turbulence intensity is at 20%. This stress level is well within the material's yield strength, ensuring the turbine's structural integrity. Moreover, the simulation results emphasize that turbulence intensity has a significant impact on the turbine's fatigue life. Further, it is predicted that an increase in turbulence intensity from 5% to 20% leads to a significant 40% reduction in the turbine's fatigue life. The stress analysis results reveal that struts, strut–blade joints, and strut–shaft joints are the key stress concentration areas. The results suggested that an increase in upstream turbulence intensity has favorable impact on turbine performance, however, for highly turbulent flows turbine should have higher strength and key areas should be focused on designing turbine for such flow conditions.