Aerodynamic Design and Assessment of a Compact, Single Stage Axial Fan for Low Noise Emission

Axial fans used in automotive and especially in locomotive cooling systems have to follow several, partially contrary specifications. In addition to geometrical and aerodynamic specifications, acoustic limits must be taken into account for new fan stage designs. Legislation will tweak axial fan requirements in the future further and further to lower their noise emission and maximize their efficiency. The main focus of this paper is to design and test a single stage axial fan for locomotive cooling systems with high aerodynamic efficiency and low noise emissions. The fan stage is designed to be installed in a so-called tower construction. The available construction space is limited. Therefore, special attention is paid to reduce the axial length. Extensive blade sweep and dihedral are implemented in the design process. The fan stage design is validated by experimental tests including aerodynamic and acoustic studies. During the aerodynamic studies, it was found that an often used approximation about the static pressure downstream the fan cannot be applied. Downstream the fan stage no further components are installed. Therefore, the static pressure at this position must be approximated. An alternative approach is developed using the results of additional studies including a downstream pipe and scaling factors. The results of the approach are plausible. The acoustic tests were carried out at a fan test facility at TU Braunschweig. To evaluate the impact of the halls acoustic repercussion on the test results, different tests were done. Additionally, another axial fan was tested which has been investigated a few years ago in an acoustic test chamber. The studies show the positive effect of the design methodology on aerodynamic and acoustic of the fan stage. All requirements were achieved as well as a reduction of the axial length of the fan stage.