Figure 4: 3D geometry of the fan
The development of a multistage axial fan using contra-rotating wheels at each stage is described here. The outer diameter of the fan is 120 mm and the rotational speed for the first and the second impeller are 133.3 s-1 and 83.3 s-1, respectively. The design of the complete fan is based upon the design approach for contra-rotating axial fans of CFturbo [12]. The first impeller was designed for a performance of 2/3 of the overall power. Hence, it was not necessary to fulfill the balancing of momentum although that is an available design option in CFturbo [12] amongst others. The contra-rotating axial fan is examined with different methods. Performance measurements and measurements on the velocity profile with optical methods (PIV) are provided to understand the working principle of every stage. The high efficiency and the axial outlet flow without tangential velocity components (swirl) are demonstrated with these measurements.