The Experimental Study of Reducing Cooling Fan Noise Using Test Bench

The blade pass frequency (BPF) noise for axial flow cooling fans in Electrical Vehicles (EV) is much obvious in some of rotational speeds. The root cause of this BPF noise is due to the cooling fan loading which is caused by the pressure difference between inlet and outlet of the fan. The pressure difference is defined as the resistance value of the fan. The resistance value of fan in EVs is much higher than the value of internal-combustion engine (ICE) vehicles. It is very difficult to obtain the resistance value in full vehicle condition. A new method to estimate the vehicle resistance value is developed using bench tests. By assuming, on the same operating parameters of the same fan both in vehicle and in test bench, such as inlet voltage, current and rotational speed, the resistance value of the fan in vehicle is the same as in test bench, thus, the operating parameters are used in the bench testing to simulate the resistance value of the fan in vehicle. Once the resistance value is achieved, the noise values of the fan can be measured in the test bench under different rotational speeds. Several testing results of different fans show that the BPF noises in bench with the defined resistance value align with those in vehicle. Using this method, the cooling fan noise can be studied in bench, earlier fan prototypes can be evaluated before finalizing design parameters. From this study it is found that the deformation of blades under the operation is the main factor to affect BPF noise levels. During operation the blade deformation changes the gap between the blade and the shroud in axial direction. The gap is related to the initial gap and the strengthen of the fan blade. This gap can be designed and optimized to balance the BPF noise in the total rotational range. The guidelines for designing low noise fan are outlined in this paper also.