Abstract:
Abstract: Numerical simulation of turbulent flow around a vane in the channel with guide vane closure based on the two-dimensional transient N-S equation was conducted with the large eddy simulation (LES) technique on Smargorinsky-Lilly model and Arbitrary Lagrange-Euler (ALE) dynamic mesh technology. In order to explore nonlinear mechanics of fluid-structure interaction between the fluid and guide vane which produced strong transient flow in the adjustment process of hydro-turbine, the Non-iterative Time Advancement (NITA) scheme was used in such a unsteady flow problem. The Reynolds number in calculation condition corresponding to chord length based on guide vane was 120 421. The model mesh was divided into triangular cell with strong adaptability. The number of mesh nodes was about 90 366, and the number of mesh elements was about 1 793 528. The finite volume method was used to disperse the LES-ALE form of transient N-S equation. The discretization of the convection term was based on the central difference scheme. The convergence of each time step in NITA scheme did not require an outer iteration. Compared with the original Iterative Time Advancement (ITA) scheme, the computation time of NITA scheme was reduced to 1/3 or 1/2. The coupling of pressure and velocity was solved by using fractional-step format. The format could save nearly 20% time compared with the PISO (pressure-implicit with splitting of operators)format in each time step. The velocity inlet and the free flow outlet were adopted in boundary condition. The non-slip boundary condition was used in the wall. The straight line of the guide vane closure law was controlled by the UDF (user defined function) method. The initial solution for unsteady calculation was used to the steady flow field by the standard k-ε turbulence model. The dynamic mesh model was used to simulate the transient process of a vane in the channel with guide vane closure. The dynamic mesh model was updated by the spring smoothing method and local remeshing method in each time step. The time step was 0.001 s. The time for a straight line closure was 6 s. The hydrodynamic characteristics and vortex induced vibration of the flow around a vane in the channel were analyzed. The fields of pressure, velocity and vorticity in the channel showed obviously unsteady characteristics. The results showed that the Karman vortex frequency was about 0.3 times of the runner rotating frequency. It was easily induced by low-frequency pressure pulsation. With the end closure of time the wake vortex morphology in the channel showed an obvious Karman vortex shedding process. The lift and drag coefficients of the guide vanes in the closing process showed nonlinear dynamic response characteristics. The formation of the low-frequency pressure oscillation was related to the Karman vortex in the tail of the vane with the closing action of the guide vanes. The nonlinear flow induced vibration by Karman vortex was the main factor that affected the hydraulic stability of hydro-turbine and the hydraulic resonance of upstream pressure conduit. The method can be used to effectively simulate the transient nonlinear fluid-structure interaction problem of hydraulic machinery.