Abstract: Numerical simulation is widely used in hydraulic design of the intake/outlet of pumped storage power stations, but its accuracy varies with the differences in mesh resolutions and turbulence models adopted. This paper evaluates these two types of errors by comparing three mesh scales and four commonly-used turbulence models through numerical simulations of the vertical intake/outlet flows at the Xilongchi hydropower station. And influence of mesh accuracy on head loss coefficient and velocity non-uniformity coefficient, among other hydraulic indexes, is analyzed for the inflow and outflow working modes of the intake/outlet. We use a grid convergence index to estimate the errors of the four turbulence models on different mesh scales and determine which scale is optimal, and examine their applicability to calculations of the two coefficients and orifice velocity distribution. The results show that all the four models on the three mesh scales satisfy convergence criteria, and mesh accuracy improves most significantly when the orifice grid size is refined from 0.05D to 0.03D. Because the results at 0.03D are close to converged solutions, further refinement has little effect on computational accuracy. Realizable is shown to be more accurate in predicting the hydraulic indexes of flows in both working modes, with prediction errors of about 5%. The results help improve accuracy in CFD calculations of vertical pipe intakes/outlets.

Key words: vertical pipe intake/outlet, bi-directional flow, hydraulic characteristics, grid convergence index, turbulence model