Mixture was separated at the volute tongue export stripping along the short tube into the separation chamber.

The results show that the performance of optimized fan is improved by lowering the energy loss which caused by the secondary flow vortex, the volute tongue, the wake-jet and the angle of attack.

The relative position between the diffusion blade and the volute tongue has influence on the distribution of diffuser flow field and the position is regulated suitably to reduce the hydraulic loss.