Numerical investigation of differential speed operation of two impellers of contra-rotating axial-flow fan

Abstract

A contra-rotating axial-flow fan is prone to stalling and motor overload at partial flow rates. Moreover, its efficiency decreases sharply at a high flow rate, which is accompanied by disparity between the shaft powers of the two impellers and the light loads of their motors. It is necessary to maintain a high fan operating efficiency and a reasonable match between the powers of the two impellers. In this study, model and simulation analyses of a mine contra-rotating axial-flow fan were conducted. Different impeller rotational speeds were obtained by controlling the pole speed. The aerodynamic characteristics, namely, the total pressure rise, shaft power, and operating efficiency, were investigated with respect to the flow rate and rotational speed combination of the impellers. The pressure and velocity distributions were also determined and analyzed. The high-efficiency operating range and variation range of the total pressure rise of the fan with different speed combinations were obtained. The findings indicate that the variable speed operation of two impellers can expand the fans’ stable operating range and that impeller speed combinations can be set based on the flow rate and the resistance of the pipe network. This enables the contra-rotating axial-flow fan to operate in the high-efficiency operating range.