Large eddy simulation of turbulent flow in a true 3D Francis hydro turbine passage with dynamical fluid-structure interaction

摘要

Results are described from a combined numerical and laboratory model study of the turbulent flow in a true 3D blade passage of a Francis hydro-turbine. The large eddy simulation (LES) is applied to investigate the intrinsic features and the spatial and temporal variations of the flow structures in the blade passage with strong wakes in inflow sweeping and the turbulence-induced blade vibration. The flow passes through the vibrating boundaries. Therefore, the system under consideration is in a dynamic fluid-structure interaction (FSI). In the simulation, one-coefficient dynamic sub-grid scale (SGS) model is incorporated in LES with Reynolds number 148 400 to better describe the energy exchange mechanism between large and small scales under the influences of strong geometrical curvature and vibrating boundaries. The governing equation of the blade vibration with FSI has been established by generalized variational principle combining the fluid and the structure. The vibration analysis is carried out by using Wilson-θ method. Separate iteration schemes are applied to solve the flow and the vibration in turn. The pressures on the wall sides of the blade and its vibrating accelerations are simultaneously measured. The numerical results show that the temporal and spatial distributions of turbulence in the 3D blade passage are significantly influenced by the curvature of blade configuration, the blade vibration, and the distorted wakes generated by flow passing through guide vanes. The influences of the vibration on the near-wall flow structures are quite remarkable. The simulated results are favourably compared with the measurements.