Numerical Study on Flow Characteristics and Energy Loss Mechanism in the 90° Circular Pipe Bend

90° circular pipe bend is used in various hydraulic pipeline system. The study of its internal flow characteristics is helpful to understand the dynamic and static performance of pipeline system and provide a theoretical basis for pipeline design. Complex phenomena of flow separation and secondary flow are obtained by numerical simulation. The separation point and the reattachment point in flow separation are less dependent on Reynolds number, but more dependent on the curvature ratio of the pipe bend. When curvature ratio Rc/D>1, the backflow disappears and the flow separation is suppressed. The energy loss mechanism in pipeline is studied by effective work analysis. Flow separation, secondary flow and dean vortex cannot do effective work, and they are the reason of energy loss caused by the flow through a 90° circular pipe bend.