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An experimental and numerical study of an automotive cooling module
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0003-0313-8614
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. , p. 69
Series
TRITA-AVE, ISSN 1651-7660 ; 2017:01
Keyword [en]
Fan installation effects, spectral decomposition, aeroacoustics
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
URN: urn:nbn:se:kth:diva-199285ISBN: 978-91-7729-195-4 (print)OAI: oai:DiVA.org:kth-199285DiVA, id: diva2:1061816
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
List of papers
1. Acoustic characteristics of a heavy duty vehicle cooling module
Open this publication in new window or tab >>Acoustic characteristics of a heavy duty vehicle cooling module
2016 (English)In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 111, p. 67-76Article in journal (Refereed) Published
Abstract [en]

Studies dedicated to the determination of acoustic characteristics of an automotive cooling package are presented. A shrouded subsonic axial fan is mounted in a wall separating an anechoic- and a reverberation room. This enables a unique separation of the up- and downstream sound fields. Microphone measurements were acquired of the radiated sound as a function of rotational speed, fan type and components included in the cooling module. The aim of the present work is to investigate the effect of a closely mounted radiator upstream of the impeller on the SPL spectral distribution. Upon examination of the SPL spectral shape, features linked specifically to the source and system are revealed. The properties of a reverberant sound field combined with the method of spectral decomposition permit an estimation of the source spectral distribution and the acoustic transfer response, respectively. Additionally, purely intrinsic acoustic properties of the radiator are scrutinized by standardized ISO methods. A new methodology comprising a dipole sound source is adopted to circumvent limitation of transmission loss measurement in the low frequency range. The sound attenuation caused by the radiator alone was found to be negligible.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Fan noise, Insertion loss, Installation effects, Spectral decomposition, Transmission loss, Acoustic field measurement, Acoustic fields, Acoustic properties, Acoustics, Architectural acoustics, Cooling, Fans, Insertion losses, Radiators, Reverberation, Wave transmission, Acoustic characteristic, Heavy duty vehicles, Reverberation rooms, Spectral distribution, Audio signal processing
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-186888 (URN)10.1016/j.apacoust.2016.04.004 (DOI)000377837700008 ()2-s2.0-84962788665 (Scopus ID)
Note

QC 20160524

Available from: 2016-05-24 Created: 2016-05-16 Last updated: 2017-11-30Bibliographically approved
2. Inclusion of Upstream Turbulent Inflow Statistics to Numerically Acquire Proper Fan Noise Characteristics
Open this publication in new window or tab >>Inclusion of Upstream Turbulent Inflow Statistics to Numerically Acquire Proper Fan Noise Characteristics
2016 (English)Conference paper, Published 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
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
urn:nbn:se:kth:diva-199277 (URN)10.4271/2016-01-1811 (DOI)2-s2.0-84978127573 (Scopus ID)
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: 2017-06-16Bibliographically approved
3. A numerical study of fan noise linked to imposed synthetic turbulence impinging the rotor
Open this publication in new window or tab >>A numerical study of fan noise linked to imposed synthetic turbulence impinging the rotor
(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
Fan noise, aeroacoustics, IDDES, SEM, FW-H
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
urn:nbn:se:kth:diva-199279 (URN)
Note

QC 20160104

Available from: 2017-01-03 Created: 2017-01-03 Last updated: 2017-01-04Bibliographically approved
4. A numerical study of noise characteristics originating from a shrouded subsonic automotive fan
Open this publication in new window or tab >>A numerical study of noise characteristics originating from a shrouded subsonic automotive fan
(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
Fan noise, Installation effects, Spectral decomposition, IDDES, FW-H, Aeroacoustics
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
urn:nbn:se:kth:diva-199280 (URN)
Note

QC 20160104

Available from: 2017-01-03 Created: 2017-01-03 Last updated: 2017-01-04Bibliographically approved
5. A numerical investigaton of aerodynamic and acoustic installation effects caused by an upstream automotive radiator
Open this publication in new window or tab >>A numerical investigaton of aerodynamic and acoustic installation effects caused by an upstream automotive radiator
(English)Manuscript (preprint) (Other academic)
Abstract [en]

An automotive radiator, situated closely upstream of an operating fan, modifies the flow field impinging on the fan blades. This in turn is reflected in the noise produced. In addition, the operating condition is changed attributed to the intrinsic pressure loss of the radiator. Further, additional structural elements scatter the sound originating from the impeller due to extraneous or intrinsic sources imposed by the radiator in the system. This paper numerically examines these effects by aerodynamically and acoustically modeling of the radiator as a porous medium. The flow field is resolved utilizing the methodology of improved delayed detached eddy simulation (IDDES) and the sound in the far-field is computed by a finite element sound propagation solver given the velocity components on an interface defined as the sound source plane. The sound pressure level (SPL) is presented for different rotational speeds and microphone positions and is compared to the measured SPL of a similar setup. The acoustic properties of the radiator alone is related to the sound transmission behavior simulated and measured. The results presented are in accordance with the behavior acquired experimentally.

Keyword
Fan noise, installation effects, radiator modeling, aeroacoustics, IDDES
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
urn:nbn:se:kth:diva-199281 (URN)
Note

QC 20160104

Available from: 2017-01-03 Created: 2017-01-03 Last updated: 2017-01-04Bibliographically approved

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