Abstract
Contra-rotating small-sized axial fans are used as cooling fans for electric equipment. In the case of the contra-rotating rotors, the blade row distance between front and rear rotors is a key parameter for the performance and stable operation. The wake and potential interference occur between the front and rear rotors and leakage flow from the front rotor tip influences on the flow condition of the rear rotor near the shroud when the blade row distance is small. Therefore, it is important to clarify the flow condition between front and rear rotors. The fan static pressure curves were obtained by the experimental apparatus and the numerical analysis was also conducted to investigate the internal flow between front and rear rotors. The leakage flow from the front rotor tip reaches the leading edge of the rear rotor when the blade row distance is small as L = 10 mm and the pressure fluctuations at the leading edge of the rear rotor tip becomes larger than those at other radial positions. In the present paper, the vorticity contour between front and rear rotors is shown and pressure fluctuations related to the leakage flow from the front rotor is investigated using the numerical analysis result. Then, suitable blade row distance for the contra-rotating small sized axial fan is discussed based on the internal flow condition.
Highlights
The vortex from the front rotor joined with the vortex of the rear rotor; the leakage flow from the front rotor tip clearance joined with the low pressure region associated with the leakage flow of the rear rotor tip clearance
The wake and potential interference between the front and rear rotors were investigated at the design flow rate Q = 0.016 m3/s with the unsteady numerical analysis
2) The strength of vorticity associated with the leakage flow from the front rotor was kept up to the entrance of the rear rotor for L = 10 mm
Summary
Power consumption has been increasing significantly in data centers, IT devices and machines because of spread of cloud computing, establishment of ubiquit-. There is a strong demand for high pressure and large flow rate of fans according to the increase of quantity of heat from electric devices. It is adequate choice to apply the contra-rotating rotors for small-sized fan because the axial space can be ensured in electrical devices as compared to that of the radial space. The influence of the blade row distance between the front and rear rotors and pressure fluctuations on the casing wall were investigated for the counter rotating fan with fan diameter D = 375 mm [4] [8]. There is the strong demand to establish the design method for small-sized axial fans based on the internal flow between the front and rear rotors. The suitable blade row distance for the contra-rotating small sized axial fan is discussed based on the internal flow condition
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