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A numerical study of fan noise linked to imposed synthetic turbulence impinging the rotor
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0003-0313-8614
(English)Manuscript (preprint) (Other academic)
Abstract [en]

A study has been conducted to numerically examine the noise generation mechanisms associated witha low-speed fan operating in a turbulent-rich inflow. Although, the turbulent content in the upstreamflow is an important aspect of the noise characteristics associated with subsonic fans, it is often omittedin numerical investigation. In this paper the turbulent structures are generated by the synthetic eddymethod (SEM) which ensures that the vortical structures imposed on the inflow boundary are temporallyand spatially correlated. The flow field is resolved using the Improved Delayed Detached Eddy Simulation(IDDES), which enables in addition to the deterministic tonal components associated with the blade passingfrequency (BPF) and its harmonics, the continuous envelope of broadband noise associated with turbulenceto be scrutinized. In the present work, the noise produced from the tip leakage flow is suppressed by aslightly less resolved tip region. Hence the effect on the noise produced associated with both the inflowturbulence and the vortices in the tip region are examined. The sound pressure level (SPL) in the far-fieldis obtained from the Ffowcs–Williams and Hawkings acoustic analogy. Validation with experimental resultsof a similar setup is provided. The results presented accentuates the need for properly constructed inletboundary conditions where turbulent structures, either part of the inflow or developed in the tip region,reinforce the noise produced.

Keyword [en]
Fan noise, aeroacoustics, IDDES, SEM, FW-H
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
URN: urn:nbn:se:kth:diva-199279OAI: oai:DiVA.org:kth-199279DiVA: diva2:1061733
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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