Unsteady Flow Condition between Front and Rear Rotor of Contra-Rotating Small Sized Axial Fan

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.

A Study on the Effect of the Outer Ring of Annular Cooling Fan on the Aerodynamic Performance

“…In addition, the backflow is caused by the existence of blade tip clearance and the pressure difference [11]. The mixing flow on the blade surface is formed by the leakage vortex, and it brings axial aerodynamic performance degradation for the axial impeller machinery [12][13][14][15]. So, the tip leakage is one of the main sources of axial-flow energy loss.…”

Optimization design of annular axial cooling fan based on circumferential vorticity analysis

“…According to Ref. [1]: for the general axial fan, the main source of secondary stream loss comes from the tip leakage vortex. The structures of shoulder and alulae added to fan blades could restrain the vortex obviously caused by secondary stream and reflux.…”

Internal Flow Condition between Front and Rear Rotor of Contra-Rotating Small-Sized Axial Fan at Low Flow Rate

“…Therefore, there is the strong demand to establish the design method for small-sized axial fans based on the internal flow. Then, the internal flow condition was investigated using the numerical models having different blade row distance L = 10 mm and 30 mm at the design flow rate [9]. Regarding the conventional axial flow fan, the relative velocity vectors and streamlines at off-design flow rate points with the deep stall condition were computed using the downstream flow resistance method [10].…”