Characterization of vortex structures with self-excited oscillations based on Liutex-Omega vortex identification method

The self-excited oscillation effect produces a continuous periodic pulsation without an external excitation source. It is widely used in fluid heat and mass transfer, cavitation and resistance reduction, and other related fields. The self-excited oscillation effect is significantly influenced by the vortex structure created by the jet passing through the specially designed cavity. The flow field in a self-excited oscillation cavity is simulated in this paper using the large eddy simulation (LES) method. The Liutex-Omega ( Ω̃_L ) method is used to analyze the vortex structure’s evolution inside the cavity and is contrasted with the Q -criterion, the γ 2 -criterion, and the Omega ( Ω ) method. The studies indicate that the Ω̃_L method is less sensitive to threshold selection compared with other methods, while it is more capable of identifying weak vortices. The change in cavity vortex structure can be devided into the four stages of vortex ring priming, growth and development, wall touch separation, and fragmentation. The turbulent energy generated by shear effect can promote the growth and development of the vortex ring structure and has an important influence on the formation of the vortex ring structure. The vortex strength reveals the interaction mechanism between the shear effect and vortex rings. The vortex core area illustrates that the small-scale vortices are mainly distributed inside the collision walls of the cavity and the downstream flow channel. The Liutex-omega method has unique advantages in analyzing the cavity flow field and revealing the mechanism of self-excited oscillations.