Focus of the research project
The project aims at the development of a low-noise contra-roating axial fan stage by conserving the high power density with respect to the acoustically demanding operating conditions. The noise reduction is achieved by a special design of the blades as well as braces with contact to the air flow. The potential of noise reduction is obtained by reducing
- the specific sound power level and the improvement of
- the psycho-acoustic parameters.
Reasons for noise sources
Sound sources can be characterised by the following figure according to Bommes (1994) and Carolus (2013).
Oppertunities of the blade design at axial fans.
Summary of noise source on fans (green: important noise sources at axial fans)
Pressure fluctuations due to transient forces at the blades are the main reasons for noise propagation. All further reasons (secondary sources, tertiary sources and stationary blade forces) are of minor importance or can not be influenced by fluiddynamical changes.
Noise Reduction
Due to the noise sources, different activities can be taken into account for reducing the noise propagation at fans. According to figure 2, following noise sources shall be in the focus of the research:
- leading edge noise
- trailing edge noise
- instability waves
- periodical separations
- large scale separations
- turbulent boundary layer
- tip vortices
Outcome
The research project aims at the application of noise reducing activities of technical and psycho-acoustical manner with a contra-rotating fan by maintaining a constant high-level power density. The whole potential of noise reduction is estimated to be
- 10 dB .
| parameter | state | aim (reduction) |
|---|---|---|
| specific sound power level | 43 dB | -5...-7 dB |
| Psychoakustik | no values | -3...-5 dB (estimated) |
Solution
The potential of noise reduction is divided into:
- the reduction of the specific sound power level and
- the improvement of the psycha-caoustics.
Throughout the research project, the following applications will be investigated:
- serrations at the trailing edge a the first whell
- sinusoidal structures at the leading edge of the second whell
- porous structures at the first whell
- serrations at the trailing edge of the first braces
- sinusoidal structures at the leading edge of the second braces
- porous elements in the shroud for reducing tip vortex noise
Following techniques will be employed to obtain a solution:
- numerical calculations (LES, RANS, URANS)
- acoustical calculations
- experiments (reverberation room, acoustical camera, PIV)
Co-operation partners
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Publications
Kercher M, Heimann J, Puhl C, Oeckel K, Friebe C and Krause R (2018), "Application of Rotational Beamforming Algorithms on fast Rotating Sound Sources", 7th Berlin Beamforming Conference 2018.
Kerscher M, Heilmann G, C.Puhle, Krause R and Friebe C (2017), "Sound Source Localization on a Fast Rotating Using Beamforming,the 46th International Congress and Exposition on Noise Control Engineering, Hong Kong, China", INTER-NOISE , HONG KONG. , pp. 626 (1-8).
Krause R, Friebe C, Kerscher M and Puhle C (2018), "INVESTIGATIONS ON NOISE SOURCES ON A CONTRA-ROTATING AXIAL FAN WITH DIFFERENT MODIFICATIONS", FAN 2018; International Conference on Fan Noise, Aerodynamcis, Applications and Systems, 18. – 20. 04. 2018, Darmstadt, Germany. , pp. 1-12.