By using the technique of turbulent large eddy simulation (LES) cooperated with the implicit stream-upwind Taylor-Galerkin finite element method, numerical simulation of the flow fields in the tortuous passage, which is similar to that of the eliminator in HVAC system, was carried out. Streamlines of the flow fields were provided and energy loss rate of every node of the mesh was calculated. According to the distribution of large eddies in the flow fields of those parts, measures of installing director blades or changing the geometric sizes can be suggested to reduce the area of large eddies and ameliorate the resistance structure. So that energy saving was achieved. It is indicated that the numerical simulation in highly density time-space mesh by using computational fluid dynamics methods is a viable method to provide basic data for the design of energy saving of HVAC system.