Figure 9. Iso-surfaces of the Q -criterion (Q = 1000 1/s2) colored by the vorticity magnitude, 0–250 s-1. (a) N = 90rpm; (b) N = 120rpm.
To evaluate the turbulence intensity quantitatively, the turbulent kinetic energy (TKE), scaled by the square of the tip velocity,U tip2, are calculated and the contour plots are shown in Figure 10. As the baffle has obvious effect on the fluid flow, the distributions of the normalized TKE on three sampling planes (as shown in Figure 2c), i.e. the middle plane between two adjacent baffles, and two planes close to the baffle, are illustrated. It is seen that the baffle location has slight influence on the TKE distribution, which implies that abundant turbulent eddies generated by the MBC agitator effectively eliminate the stagnant zone before and after the baffle. In addition, the TKE distributions are compared with those generated by RT impeller, which have the configuration size of D = 1/3T and D = 1/2Tand have been predicted in our previous work19. It is observed that not only the TKE level is higher than that of the conventional RT impellers, but also the TKE distribution is much uniform for the MBC agitator. One can see that the TKE values in most regions are larger than 0.04 for the MBC agitator, whereas in the tank with RT impellers, there are only a few regions can reach such a TKE level, even in the case of D /T = 1/2.