Unsteady hydraulic characteristics in large-diameter pipings with elbow for JSFR, 2; Studies on applicability of a Large-Eddy Simulation to high -number short-elbow pipe flow

Eguchi, Yuzuru*; Murakami, Takahiro*; Tanaka, Masaaki  ; Yamano, Hidemasa   

Since unsteady force possibly generated by fluid motion in a short-elbow pipe needs evaluating in the JSFR plant design, applicability of large-eddy simulation (LES) method to a high number water test is studied with an in-house LES code in the paper. First, requirement for mesh subdivision at high- LES computation is theoretically studied. Then, the effects of turbulence model and boundary conditions are numerically studied using the Smagorinsky model and the WALE (Wall-adapting local eddy-viscosity) model with various inlet and outlet boundary conditions at = 1.210. It has turned out that the Smagorinsky model excels the WALE model and that an inlet velocity profile has a considerable impact on the separation features at the elbow curvature. It was also revealed that the outlet boundary condition is likely to have an effect on the separation features especially if the distance between the elbow and the outlet is rather short, which is the case of the present computation. Basic features of the pressure and the wall force fluctuations are also discussed with the aid of computational visualization and spectral analysis.