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([Math Processing Error])method is used to analyze the vortex structure’s evolution inside the cavity and is contrasted with the Q-criterion,the λ_(2)-criterion,and the Omega(Ω)method.The studies indicate that the[Math Processing Error]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.

Study on mathematical model of cutting force in micromachining

With the development of micromachining technology,it is very important to study the mechanism of micromachining,determine the micromachining parameters and ensure the products’quality during the micromachining process.Combined with the micromechanism between tool and workpiece during micromachining process,the sources of the micro-cutting force were analyzed,the micro-cutting physical model was constructed,and the microstress model interacted between the cutting arc edge of the tool and the material of the workpiece was analyzed.Combined with the surface friction and elastic extrusion mechanism between the cutting tool and workpiece,the micro-cutting force model was constructed from two aspects.The micro-cutting depth is deeper than the minimum cutting depth and the micro-cutting depth is shallower than the minimum cutting depth,then the minimum cutting depth value was calculated.Combined with the dislocation properties and microcrystal structure of workpiece’s material,the internal stress of the micromachining force model based on the gradient plasticity theory was calculated,and the force model of the micro-cutting process was studied too.It is significant to control the precision of micromachining process during the micromachining process by constructing the micromachining process force model through studying the small deformation of the material and the mechanism of micromachining.