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Inclusion of Upstream Turbulent Inflow Statistics to Numerically Acquire Proper Fan Noise Characteristics
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0003-0313-8614
2016 (English)Conference paper (Refereed)
Abstract [en]

To obtain realistic noise characteristics from CAA studies of subsonic fans, it is important to prescribe properly constructed turbulent inflow statistics. This is frequently omitted; instead it is assumed that the stochastic characteristics of turbulence, absent at the initial stage, progressively develops as the rotor inflicts the flow field over time and hence that the sound generating mechanism governed by surface pressure fluctuations are asymptotically accounted for. That assumption violates the actual interplay taking place between an ingested flow field and the surface pressure fluctuations exerted by the blades producing noise. The aim of the present study is to examine the coupling effect between synthetically ingested turbulence to sound produced from a subsonic ducted fan. The steady state inflow parameters are mapped from a precursor RANS simulation onto the inflow boundaries of a reduced domain to limit the computational cost. The flow field is resolved utilizing IDDES for turbulence handling and the computational domains are configured for both a single blade and a circumferential complete five bladed fan. The results clearly reveal the limitations of restricting the computational analysis to a single blade. Additionally, a separate investigation of the upstream inlet section shows that the deterministic flow structures generated at the inlet plane are selfsustained within the inlet section. The outcome stresses the importance of incorporating correlated inflow statistics for turbomachinery noise studies. Moreover, the acoustic analogy formulated by Ffowcs -Williams and Hawkings is employed to study the low frequency spectral distribution. Previously conducted measurements are used for validation of both the flow field statistics and the far-field sound field.

Place, publisher, year, edition, pages
SAE international , 2016. Paper 2016-01-1811
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
URN: urn:nbn:se:kth:diva-199277DOI: 10.4271/2016-01-1811OAI: oai:DiVA.org:kth-199277DiVA: diva2:1061727
Conference
9th International Styrian Noise, Vibration & Harshness Congress, The European Automotive Noise Conference
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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