In this paper

a new design

named combined cascades

which is applied to blade design of reversible axial fan

is put forward based on the assimilating of the previous experience

the advanced technology and the up to date thinking.A new criterion for judging the blade performance in reversible axial fan is presented.NACA0012 airfoil is singled out as the experimental airfoil of the combined cascades.In the two dimensional wind tunnel experiment

the comprehensive performance of the combined cascades is understood through analyzing pressure contours of both the blades and substantive data got from inlet and outlet of cascade at the different overlap ratios

pitch ratios and attack angles.Based on analyzing and comparing results gotten from experiment

it is found that the aerodynamic characteristic of combined cascades is superior to any other cascades.Compared with S type airfoil

which is specifically designed for reversible axial fan

maximum lift coefficient C N+R y max of the symmetrical combined cascades is improved by about 20% and the stall attack angle α N+R C y max about 23 5%.And with NACA0012 single cascade

lift coefficient increases by 8 46% and the stall attack angle 17 5%.The unique flow rules of the combined cascades are understood through analyzing data.The flow in the combined cascades must meet the flow prerequisite i.e.the static pressure must be equivalent along the pitch wise at the outlet of the fan.The overlap ratio B is the one of the most important parameters by which the relative position of two rows of cascade could be determined.As B is chosen within 30%～50%

two rows could be operated respectively at their own stall attack angles and the cascade performance could be improved obviously.The pitch ratio T is another important parameter and could effect cascade performance directly.The smaller T is more suitable to the cascade performance and the optimum range should lie in between 40% and 50%.