Speed Matching of the Second Rotor in a Counter-Rotating Fan Under Off-Design Conditions

A method for speed matching of the second rotor (R2) with equal power for two rotors was proposed to improve the performance of the counter-rotating fan under off-design conditions. In this method, the speed of R2 is adjusted until the power of R2 is equal to the power of the first rotor (R1). The fan performance during constant speed operation and during R2 speed matching operation is presented and discussed using theoretical analysis, numerical simulation, and experimental research. The results show that R2 speed matching improves the power and efficiency characteristics of R2. Thus, the pressure rise and power characteristics of the fan were improved. The load of R2 under low flow rates condition was decreased, and the pressure rise and efficiency of R2 under high flow rates condition were increased. The blocking condition margin increased from 37.2% to 48.0%, and the high-efficiency working range of the fan increased from 33.2% to 37.9%.