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A numerical study of noise characteristics originating from a shrouded subsonic automotive fan
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0003-0313-8614
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The characteristics of the noise radiated from a reduced automotive cooling module is numerically studied with focus on the interaction effects linked to the sound generation mechanisms and the acoustic scattering caused by the confined installation. The flow field is simulated by adopting the formulation of IDDES, which is a numerical technique that enables large scale structures to be resolved and the wall-bounded flow to be treated either in DDES or WMLES depending on the turbulent content within the boundary layer. By comparing the simulated fan performance to two sets of experimental data of a similar setup, the aerodynamic results obtained from IDDES are validated and conformed to the volumetric flow rate delivered for the pressure drop measured. The acoustic part of the study comprises evaluation of the sound source associated with the momentum distribution imposed on the surroundings at an interface slightly upstream the fan. At the microphone positions upstream the installation, the SPL falls within the SPL range measured and the acoustic power delivered by the fan conforms to the SWL obtained from the comparison method in the reverberation room. The system response function, estimated by subtracting the SWL for the free-field simulation from the SWL associated with the reduced automotive cooling modulemarks spectral humps at fixed frequencies, irrespectively of sound source. As such, the engineering approach to spectral decomposition method earlier published which, enables isolating the acoustical properties of the installation from the source, is validated and found to hold.

Keyword [en]
Fan noise, Installation effects, Spectral decomposition, IDDES, FW-H, Aeroacoustics
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
URN: urn:nbn:se:kth:diva-199280OAI: oai:DiVA.org:kth-199280DiVA: diva2:1061739
Note

QC 20160104

Available from: 2017-01-03 Created: 2017-01-03 Last updated: 2017-01-04Bibliographically approved
In thesis
1. An experimental and numerical study of an automotive cooling module
Open this publication in new window or tab >>An experimental and numerical study of an automotive cooling module
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Heavy vehicles are major emitters of noise. Especially at idle or low vehicle speeds a large portion of the noise emanates from the fan that forces the flow through the cooling module. The aim of this work is to investigate and reveal aerodynamic and acoustic installation effects linked to the cooling package. This introduces a multidisciplinary approach involving examination of the flow field, sound generation and sound propagation. The work includes two main parts: an experimental and a numerical part. The cooling module used throughout this work, named reduced cooling module, primarily includes a radiator, a shroud, a fan and a hydraulic engine to simplify the aeroacoustics analysis.

The experimental part comprises measurements of the sound emanated from the cooling package. A new approach to the spectral decomposition method is developed yielding the fan sound power or spectrum to be formulated as a product of a source part and a system part scaling with the Strouhal number and the Helmholtz number. Also, a separate determination of the transmission loss of the radiator is performed. The impact of the radiator on the transmitted noise was found to be negligible.

The numerical part incorporates comparisons from two aeroacoustics studies; a configuration where the fan is forced to operate at a fixed operation point and measured flow and turbulence statistics are available and the reduced cooling module. A hybrid turbulence modeling technique, IDDES, is adopted for the flow simulations. The sound propagation is calculated by the Ffowcs-Williams and Hawkings acoustic analogy when assuming a free-field sound propagation and by a finite element solver in the frequency domain to capture the installation effects. The simulated SPL conforms to the measured SPL and the blade response to the turbulent inflow and to the tip resolution, respectively, produce noise which spectral shape distribution is modified in accordance with earlier experimental findings published. Furthermore, the influence of an upstream radiator in close contact with the fan on the flow and sound fields is investigated. Here, the simulated aeroacoustic characteristics were found to change similarly to the acoustic measurements with and without radiator.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. 69 p.
Series
TRITA-AVE, ISSN 1651-7660 ; 2017:01
Keyword
Fan installation effects, spectral decomposition, aeroacoustics
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
urn:nbn:se:kth:diva-199285 (URN)978-91-7729-195-4 (ISBN)
Public defence
2017-01-27, D2, Lindstedtsvägen 5, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2017-01-03 Created: 2017-01-03 Last updated: 2017-01-03Bibliographically approved

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