Numerical Investigation of Axial Fans in Serial Connection

C3 - CFD Validation Studies

Compact fans are often used for electronic cooling for example in telecom base stations or large computer servers. In many cases two axial fans are operated in two-stage configurations, sometimes six or more of those sets are used per application. Most of the time, these fans are operated at lower part load only in case of failure of one fan the remaining fan will speed-up to avoid a local pressure drop or flow short-cut in the application. Another reason for multistage arrangement of fans is to get an overall performance curve towards more pressure. Typically, two identical standard fans are used for this purpose, sometimes with flow straighteners in between. For this study, a two-stage set-up of compact fans with impeller diameter of 75mm is investigated by 3D numerical methods. Steady and unsteady calculations of different arrangements are investigated and the results are compared to experiments. It can be shown, that a proper arrangement of two axial fans will increase both static pressure rise and flow rate. In addition to the aerodynamic performance, the acoustic behavior of the different set-ups is presented. It is shown, that the arrangement itself and the additional components have significant impact on the acoustic behavior with respect to sound power and sound quality.