Comparative assessment and analysis of Rortex vortex in swirling jets

Recently, a new definition, called Rortex, was proposed to quantify the purely rotational motion of fluids. In this work, based on the DNS data, the Rortex is used to assess and visualize the rotational motion and structure of the vortex in swirling jets in comparison with other kinds of vortex criteria, including Q , λ2,vorticity and Ω criteria. The Rortex vector,Ω, Q and criteria are found to be better than the vorticity criterion for the vortex core identification. The vector triangle formed by the Rortex R , the nonrotational shear S , and the vorticity R is analyzed to give mechanical explanations, especially of the effect of the non-rotational shear on the rotation of fluids. In addition, the probability density distributions (PDF) of the Rortex R , the nonrotational shear S, and the vorticity R are computed. The peak value of the PDF of the vorticity could be used to explain the pure rigid rotation effect and the combination effects of the rigid rotation and the non?rotational shear.

Analysis and correlation of fluid acceleration with vorticity and Liutex(Rortex)in swirling jets

The characteristics of the acceleration a and its correlation with the vortex core in the swirling flow are analyzed in this paper.The swirling flows of four swirl numbers(Sn=n S 0,0.10,0.20 and 0.36)are simulated by the direct numerical simulation,and the fluid mass particles from the inlet of the swirling flow are traced as a database for the current study.The correlations of the acceleration a with the vortex identification parameters of R andωare quantified,where R is the parameter of the“Liutex”-method proposed by Prof.Liu,and its early version is“Rortex”.The probability density functions of the included angles of a-R and a-ωare computed,which are used to clarify the geometrical configuration between a and R.The covariance coefficients between a and the parameters of various vortex core criteria(Q,λ2,ΩL,ΩR,ωand R)are computed and their relative levels of correlation are compared.Compared to the velocity,the expectation and the rms of the acceleration magnitudes and its projections on R and the plane perpendicular to R are computed for better explaining the correlation features between a and R.It is found that a and R are always either perpendicular or parallel to each other with the quantized included angles of∠(a,R)=kπ/2,(k=0,1,2).This confirms the role of R which works as the axis of the vortex exclusively.

Liutex-based analysis of drag force and vortex in two-phase flow past 2-D square obstacle using LBM on GPU

The two-phase flow past a square is a ubiquitous phenomenon widely encountered in industries and engineering,where the interaction of disparate phases coupled with the influence of the solid is rather complicated.In this context,the flow characteristics and the vortex field are investigated to reveal the mechanisms of the two-phase drag and the vortex variation.The lattice Boltzmann method(LBM)is utilized to study the multi-component two-phase flow.The computation implemented on the GPU is remarkably accelerated thanks to the natural parallelism of the LBM.The process of the two-phase flow past a square is thoroughly examined.The drag and lift forces,including the total force and the components caused by the dispersed phase and the continuous phase,respectively,are obtained,and their variation mechanisms are explained.Meanwhile,the vortex-identification approaches based on the Liutex as well as the traditional methods are compared.The relationship between the bubble breakup and coalescence processes and the extremums of different vortex identification variables is analyzed.