## 5 Results and Discussion  
### Effect of Baffle Structure on Flow Field  
Central agitation would generate a circumferential periodic flow field, and flow state analysis was conducted by extracting the vortex structure in the tank. Figures 7 and 8, respectively, show the flow fields of different relative tooth heights (\(A\)/\(W\)) and relative tooth widths (\(\lambda\)/\(h\)) on the impeller section. The results show that the circulating fluid would form a flow dead zone before and after the baffle because the baffle would generate a certain flow resistance. As shown in Figures 9 and 10, there was a low-speed region in the range  
Figure 5: The average velocity of fluid with different mesh numbers compared with the experiment (y = 0.25 h).  
Figure 6: The average velocity field of a fluid. (**a**) The PIV experiment; (**b**) the CFD simulation.  
of r/R = 0.8-0.9. Compared with the standard baffle (r/R = 0.75-0.9), sinusoidal cutting was carried out on the edge of the baffle to make the vortex center close to the wall of the mixing tank, eliminate the small reflux vortex caused by obstruction in front of the baffle, and reduce the reflux flow behind the baffle. A prediction could be made that the reduction of the vortex area would be beneficial for improving the mixing effect and reducing the power consumption.  
Figure 8: The velocity streamline distribution (\(\psi/h\) = 0.25) of the baffle with different relative tooth widths (\(\lambda/h\)) when \(A/W\) = 0.333.  
Figure 7: The velocity streamline distribution (\(\psi/h\) = 0.25) of the baffle with different relative tooth heights (\(A/W\)) when \(\lambda/h\) = 0.104.  
Figure 9: A comparison of the average velocity along the radial direction (\(\psi/h\) = 0.25) of the baffle with different relative tooth heights (\(A/W\)) when \(\lambda/h\) = 0.104.  
Unlike the serrated trailing edge of the fan, the fluid was relatively perpendicular to the serrated baffle during the stirring process. Limited by the width of the baffle, the tooth height could only be changed in a small range, and thus the change of the relative tooth height (\(A\)/\(W\)) causing the change of the vortex behind the baffle was not obvious. In contrast, the reduction of the tooth width made the backflow behind the baffle tend to weaken. When \(A\)/\(W\) = 0.333 and \(\lambda\)/\(h\) = 0.028, the recirculation dead zone behind the baffle was significantly reduced, as shown in Figure 8b.  
Figure 11 depicts the radial and tangential velocity distributions of the fluid on the impeller plane. The negative value in Figure 11a can be attributed to the fluid being unable to pass directly through the baffle area for the obstruction of the baffle; thus, a vector was pointing to the axis. The notch on the edge of the sawtooth baffle allowed part of the fluid to pass through the notch to merge with the fluid bypassing the baffle, which weakened the baffle's blocking effect on the fluid and reduced the fluid flow resistance; thus, the negative value of the radial velocity was small. The change of radial velocity enhanced the annular motion of the fluid. In the annular flow domain between the blade and the baffle (r/R = 0.6\(\sim\)0.9), the tangential velocity of the sinusoidal sawtooth baffle was significantly higher than that of the standard baffle.