Prediction accuracy assessment
LES requires high-resolution meshes when solving turbulence problems, in particular, near the solid impeller where the viscous sublayer needs to be solved accurately. The dimensionless wall distance, Y+ , is usually used to evaluate the grid resolution near the wall andY+ < 5 is a consensus criterion for LES prediction. In this work, the Y+ values are firstly calculated and those around the MBC impeller are shown in Figure 3. It is clearly observed that the Y+ values are less than 2 in most areas, and all are smaller than 5, which implies that good simulation accuracy is to be expected.