Experimental investigation on the effect of load distribution on the performances of a counter-rotating axial-flow fan

Overview & Synopsis

A counter-rotating axial-flow stage consists of two fans that rotate in opposite direction. In the design procedure, parameters such as the angular velocity ratio and the repartition of the work performed by each rotors are to be chosen. In the present Article, three counter-rotating stages are designed to meet the same working point. These stages have different repartitions of load between the front and rear rotor, different angular velocity ratios or mean stagger angles of the blades of the front rotors. The stage global characteristics and the unsteady features of the flow between the counter-rotating rotors are measured and compared. The three systems all have satisfying overall performances at the design point. Strong differences are observed in the flow field at partial flow rates, the rear rotor reducing the hub recirculation. The behaviour at partial flow rates is thus triggered by the rear rotor characteristics. The best compromise is obtained with a repartition of the loading of 60% for the front rotor and 40% for the rear rotor, with almost equal angular velocities.