In order to increase the systematic understanding for the internal flow field of an ejector,and provide reference for the design and modeling of ejectors,the internal flow field and performances of the ejector were studied by means of numerical analysis in this paper. The results show that when entrainment vortex is the dominant factor affecting the characteristic of the mixing layer,it is appropriate to use an eddy boundary line to characterize the distribution scope of phase. Moreover,it is appropriate to...