Abstract: The effects of the main geometrical parameters of the submerged vortex generators on the diffuser performance are analysed.A combination of corotating and counter rotating votex generators was used in the study.In the center part of the channel,four pairs of counter rotating vortex generators were used to eliminate the flow separation.At the two corners,two corotating vortex generator blades and one pair of counter roataing blades were used respectively to improve the three dimensional separation flow fields in these corner regions.The experimental results show that the static pressure recovery coefficient C P is enhanced remarkably and the total pressure loss is also reduced,if the geometrical parameters and the location of the vortex generators are selected properly.A comparative study between the submerged vortex generators of concave shape and the conventional vane type vortex generators is also presented.Both of them have almost the same efficiency for separation control,but the parasitic drag of the former is less due to its submergence in the boundary layer;and it is convenient for practical application because its distance to the separation starting point on the diverging wall of the generator is much shorter.