Developing Efficient Compact Fan Guide Vanes with TURBOdesign1

A case study by ebm-papst

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Introduction

Ebm-papst was founded in 1963 by Gerhard Sturm, still actively heading the company, and Heinz Ziehl. Everything started with the external-rotor motor which was rediscovered then as an ideal drive for small fans. As the pillar and basic principle of our innovative and wide product range, the external-rotor motor made Ebm the world market leader. In the 1970s, both Ebm and Papst were innovators in the field of brushless EC drives. This guaranteed them an important edge in terms of know-how that they have been able to maintain right up to the present day. In 1992, Ebm took over PAPST Motoren GmbH & Co. KG, following this up in 1997 by acquiring MVL Motoren Ventilatoren Landshut GmbH. The Ebm, Papst and MVL companies took the joint brand name Ebm-papst in 2003.

 

Slice for velocity distribution

 

Today, with approximately 10,000 people in 57 subsidiaries and 17 production facilities worldwide, Ebm-papst produces high quality fans and motors for many markets such as heating and air-conditioning, ventilation, refrigeration, automotive, IT/telecom and drive technology. The turnover of the whole group was 1,076 million in the fiscal year 07/08. The Ebm-papst product portfolio comprises about 14500 different items and the global production in 2007/08 was 55.6 million fans and motors.

High requirements concerning durability and noise and high efficiency are the drivers in these markets.

Challenge

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.

 

Compact fan with guide vanes

 

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.

 

"After using TURBOdesign1 for numerous years, we no consider it our standard design tool for radial, diagonal and axial fans".

Guide Vane Design

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.

 

Efficiency improvement - Blue guide vanes, Red: same rotor without guide vanes

 

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.

 

Circumferentially averaged velocity profiles downstream the rotor, used as an TURBOdesign1 input parameter

 

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 no consider it our standard design tool for radial, diagonal and axial fans”.

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