Aeroacoustical Investigations on Axial Fans for Automotive Cooling Systems

E1 - Noise of Cooling Fans in Automotive Applications

The noise emission of axial fans for automotive cooling systems has considerable contribution to the sound emission of the vehicle. The target of many investigations is to find measures to reduce the noise of the fan. For this purpose, an understanding of the different noise generating mechanisms is essential. To analyze the influence of important characteristic parameters, like gap shape, the number of blades, the blade spacing and skewed blades, time equivalent measurements of the noise propagation were carried out. The main focus is the change of the geometry while keeping the blade loading constant. The scope of this project is to investigate the influence of skewed blades to the aerodynamic and acoustic behaviour of axial fans. Therefore axial fans with different skewed geometries were built and measured. The variations include unskewed, backward and forward skewed blades. The strength of the skew is also a variation made in this approach and include different form for forward skewed axial fans. The aerodynamic comparison between the different skewed fans shows a very satisfactory result, as the prescribed goal, same aerodynamic condition, has been achieved. All the measured characteristic graphs of the different fans show very small difference, especially in the range of the best point and for a given system curve. The comparison of the efficiency shows an increase by the backward skewed fan in comparison to the unskewed fan and the small displacement of the best point to higher volume flow coefficient. In the case of the forward skewed fans the efficiency decreases with the increase of strength of skew, while the point of maximum efficiency moves to smaller volume flow. The comparison of the acoustic graphs shows the best result with the strong forward skewed axial fan. To explain the lower efficiency in the case of the forward skewed axial fan and the best result in the noise propagation, numerical investigations were carried out. The simulated characteristic aerodynamic curves of the different variants show a good agreement with the measured graphs. Especially the trends between the unskewed and different skewed axial fans are very well reproduced.