Vortex Identification And Dynamics Research Based On Liutex

Turbulence is a worldwide problem,and turbulent vortex is even more mysterious.Therefore,the exploration of vortex definition and identification is particularly important.In recent years,liutex has made a new definition of vortex based on pure rigid rotation,and proposed the corresponding liutex vortex identification method,which has been applied and verified in many fields.Therefore,this thesis uses the liutex vortex identification method and four new vortex identification methods proposed by us to identify the vortex structure of boundary layer flow and cylindrical Carmen vortex street,and studies the relevant dynamics based on liutex.The specific research contents and results are as follows.(1)Firstly,the vortex structure in the boundary layer of a flat plate flow process is identified by using the liutex vortex identification method.The vortex structure characteristics and evolution law of flat plate boundary layer flow from transition to turbulence are summarized.Then,the vortex structure of the flow around the cylinder is identified by liutex.It is found that liutex’s vortex identification method can be well used to identify the vortex structure of the flow around the cylinder.(2)Based on the problem analysis of vorticity in expressing the rigid rotation of fluid,the definitions of new vorticity and new strain rate are proposed.The new definition holds that only when the product of the two gradients contained in the vorticity and strain rate components is negative,the fluid can represent rotation in this direction;When the product of the two velocity gradients is nonnegative,the fluid has shear.Based on this,we modify the vorticity,Q method andΩmethod,and propose three new vortex identification methods,namely new vorticity method,new Q method and newΩmethod.(3)The magnitude of the two velocity gradients in the new vorticity component is further discussed and analyzed,and a vortex identification method based on real rigid rotation is proposed,which is called_method.In this method,the smaller absolute value of the two velocity gradients contained in the new vorticity component represents rotation,and the sum of the two velocity gradients represents shear in all cases(the same sign,different sign,at least one of which is 0).(4)With the powerful data processing ability and convenient graphic function of MATLAB and Tecplot,various vortex identification methods are used to identify the vortex structure of boundary layer transition and boundary layer turbulence.The results show that the four vortex identification methods proposed in this thesis(New vorticity method,new Q method,newΩmethod and_method)can better identify the vortex structure in the flat plate boundary layer,It also proves the rationality of our definitions of new vortex identification method and new strain rate to a certain extent.Then,the_method with excellent effect is used to display and analyze the vortex structures appearing at different thresholds in the transition front region of the slab boundary layer.(5)A new flow constitutive equation is established based on liutex and Stokes hypothesis,and its strain rate and stress are no longer symmetrical.At the same time,we deduce the momentum equation based on the new constitutive equation.Compared with the original N-S equation,it is found that there is an additional force due to liutex rigid rotation in the new equation.When the fluid is incompressible and non rotating,the new equation degenerates to N-S equation.Finally,the DNS data of the boundary layer flow of the plate are used to compare the old and new viscous stress formulas on the plate.The results show that the calculation results of the transition and turbulence parts of the plate are basically consistent.However,the rationality and reliability of the equation need further theoretical,numerical and experimental research.