Developing Efficient Compact Fan Guide Vanes with TURBOdesign1

Compact fans are used for cooling of electronic components. Key industries are IT and Telecom. High requirements concerning durability and noise and high efficiency are the drivers in these markets. Due to the compact design, the majority of these fans have a relatively large hub-to-tip ratio (v=d /D). This leads to comparatively high outlet losses. Therefore, the diffuser design has to be carried out carefully.

The goal of each diffuser is to decelerate the meridional velocity c in order to recover static pressure. Another method is to apply guide vanes behind the rotor. In this case, the reduction of the spin component c is important to gain a higher level of efficiency (in terms of static pressure recovery). The aim is to design the guide vane in such a way as to give zero exit swirl velocity from the fan if there is sufficient space available.

To gain a high level of static pressure recovery, the guide vane design is very important. On one hand the aerodynamic loads between the rotor blades and the guide vanes have to be balanced on the other hand the incident air flow to the guide vanes is important to minimize losses.

Due to this fact, it is very important to determine the outlet velocity profiles of the impeller. An appropriate operation point is chosen using state-of-the-art CFD methods. The velocity profiles are extracted from the CFD results and the radial profiles of the circumferentially averaged data are used as boundary conditions for TURBOdesign1 to design the guide vanes (Fig. 4). The advantage of using a 3D inverse design method such as TURBOdesign1 is that the code automatically designs the guide vane to match the upstream variation in spanwsie velocity. The resulting blade usually satisfies the expected upstream flow field and minimum exit kinetic energy. As a result the level of static pressure recovery could be increased considerably with this technique. Fig.3 shows the comparison of a compact fan with and without guide vanes. The static efficiency of the fan with guide vanes could be increased significantly.

Summary

The possibility to generate different designs in a fast and robust way makes TURBOdesign1 an integral part of the work flow for designing multi-row fans with guide vanes at Ebm-papst St. Georgen. “After using TURBOdesign1 for numerous years, we now consider it our standard design tool for radial, diagonal and axial fans”.