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.