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.