Experimental Study on the Speed Matching of Two Rotors for a Counter-Rotating Fan

A method for the speed matching of the second rotor (R2) with equal power for two rotors was proposed to avoid the overload of the second motor under low flow rate and the rapid decrease in pressure-rise and efficiency of R2 under high flow rate. The speed matching of two-stage rotors is proposed and analyzed to improve the stability margin of the counter-rotating fan (CRF). The fan performances during constant speed operating and during the speed matching operating are presented and discussed using experimental research. The results show that, the speed matching of R2 operating decreases the load of R2 under low flow rate and increases the pressure-rise and efficiency of R2 under high flow rate. Thus, the efficient working range and the blocking condition margin are increased. Reducing n₁ and increasing n₂ under low flow rate can regulate the position of unstable working line leftward without reducing the pressure-rise of the fan. Thus, the stability margin of the CRF is expanded.