## 2 Proposal and Description of the Novel Impeller  
The mixing quality depends on the flow field of the stirred tank. [PERSON] et al. [26] clearly pointed out that the formation of the recirculation cells of the stirred tank is an obstacle to solid-liquid mixing. In addition to the overall turbulence level, the uniformity of turbulence in the stirred tank is also essential. Since the energy injected by the impeller decays rapidly from its vicinity, it is difficult to achieve high uniformity. The impellers may need to have higher rotation speeds to reach the target level of homogenization, and energy consumption may become a problem worthy of attention. Therefore, an ideal optimization design would achieve high mixing quality and low power consumption.  
The blade surface is changed by adding holes on the impeller. A hole can reduce the resistance during rotation (thus saving input power), and the edge of the hole plays a role in the generation of turbulence. Due to the increase of shear times, the micro mixing efficiency is increased. Bionics has made great progress in improving aerodynamic and hydraulic properties. Biological structures have a number of characteristics, for instance, that the flow field is evenly distributed. Bionic design is a new design method that applies the laws and mechanisms of biology to improve product performance. It can effectively improve the turbulent boundary layer and velocity distribution of the flow field, reducing the resistance and improve the efficiency. The possible benefits of bionic airfoils include controlling the flow around the blade, inhibiting the flow separation at the large inlet angle, controlling the tip vortex, delaying stall and improving the lift-drag ratio [27]. Previous studies [28] have shown that changing the blade surface can improve flow characteristics in the stirred tank. Bionic cuts can interfere with the regular movement of the fluid, help to break the mixing isolation zone, have a key impact on the wake vortex structure and energy dissipation, and play a positive role in reducing power consumption.  
Based on the potential benefits of perforation and bionics, three novel impellers with different structures were proposed in this paper by introducing apertures and bionic cuts into the traditional impeller (PBT), the geometric dimensions of the conventional impeller (PBT) and the novel impellers (PBPT, BCBT, and BCPBT) are shown in Figure 2. PBT is commonly used in the solid-liquid mixing processes of industrial applications. PBPT adds holes to the blade surfaces of the PBT. Inspired by bionic design, BCBT has bionic cuts on the edge of the PBT. The contour of the bionic cuts is a sine function curve, and its shape is determined by the wavelength and amplitude. BCPBT combines the holes and bionic cuts. Compared with the traditional impeller optimization design, BCPBT has the advantages of promoting turbulence uniformity and enhancing mixing because of holes and bionic cuts. These impeller structures are determined by impeller diameter, \(D\), blade width, \(W_{i}\), blade length, \(b\), aperture diameter, \(d\), aperture ratio, \(\beta\), wavelength, \(\lambda\), amplitude, \(A\) and other structural parameters. The basic dimensions of the impeller are summarized in Table 1. The change of each structural parameter may have a significant impact on mixing efficiency.