First of all, the distribution of the CV on fan blade should be caught by data post-proceedingafter simulation. As shown in Fig. 7, positive and negative CVs are both distributed on the fanblade. There are obvious negative CV distribution concentrates on the fan tip and it along thedirection from the leading edge to trailing edge, although they are not belonging to the sameaperture rate annular fan. To explain the phenomenon mentioned above, further observation ofspecific velocity vector around fan is carried out as shown in Fig. 8. For annular fan with lowaperture rate, there is a smaller area of the negative CV than that with a higher aperture rate.