Blade Tip Flow of Contra-Rotating Small-Sized Axial Fan at Design Flow Rate

Small-sized axial fan is used as air cooler for electric equipment. But there is strong demand for higher power of fan according to the increase of quantity of heat from electric devices. Therefore, higher rotational speed design is necessary, however it causes the deterioration of efficiency and increases the noise. Contra-rotating axial fan is smaller than conventional axial fan under the same rotational speed, and is effective for lower rotational speed design under the same diameter. So, the adoption of contra-rotating rotor for small-sized axial fan was proposed for the improvement performance. In the present paper, the unsteady numerical analysis was conducted to investigate the performance and flow field in contra-rotating small-sized axial fan rotors at the design flow rates. Further, the ideal blade row distance of the contra-rotating small-sized axial fan was clarified with the unsteady numerical analysis results.