Flow instability study in 180° curved duct using energy gradient theory

Flow stability and turbulent transition are important research topics in fluid mechanics and fluid machinery. In this paper, the energy gradient theory is used to examine the instability of flow in 180° curved duct with rectangular cross-section. Based on the assumption that the base flow is laminar flow, the distribution of the energy gradient function K is obtained by three-dimensional numerical simulation under different Reynolds number. Compared with experimental results, it is found that the position of the maximum of K is the place where fluid is first to lose its stability, then forming a vortex. With the increase of Re, the flow gradually transits into turbulence. The distribution characteristics of K calculated by numerical simulation is in agreement with the instability zones implied by experimental data.