Water header is the most common structure in the design of flow system for
energy and power system. The complex flow structure could result in some
problems when Computational Fluid Dynamic (CFD) simulation is applied in the
whole system analysis. The rapid change in velocity distribution of the flow
field leads to difficulties to create suitable boundary layer mesh, and the
complex flow structure will also make residuals hard to reach convergence
criteria. Large Eddy Simulation (LES) is promising to promote these studies,
it is more accurate than RANS method and can capture many non-steady state
characteristics those RANS method can?t obtain. In this study a typical
water header flow structure is investigated by RANS and LES methods. By
comparing the detailed flow structures in the results of two methods, the
deficiency of RANS method was found. The results of LES can be used to guide
the establishment of meshes and the application of time-averaged turbulence
models to improve efficiency in engineering. And the asymmetric Reynolds
stresses may induce asymmetric flow field in symmetric geometry.