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Predicting flow-generated noise from HVAC components
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.ORCID iD: 0000-0002-6811-056X
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

More energy efficient fans, i.e. larger sizes running at lower speeds, in Heating Ventilation and Air Conditioning (HVAC) systems decrease the fan noise and increase the importance of flow generated noise in other system components, e.g., dampers and air terminal devices. In this thesis, an extended prediction model, using semi-empirical scaling laws, for flow noise prediction in HVAC systems at low Mach number flow speeds is presented. The scaling laws can be seen as a combination of a generalized noise spectrum based on experimental data and constriction flow characteristics, where the latter can be gained from ComputationalFluid Dynamics (CFD) simulations. The flow generated noise can be predicted by semi-empirical scaling laws to avoid a time consuming, fully resolved simulation or measurement. Here, an approach is suggested where the general noise spectra are combined with turbulent data obtained from Reynolds Average Navier Stokes (RANS) simulations. A model is proposed using a momentumflux assumption of the dipole source strength and a frequency scaling based on the constriction pressure loss. To evaluate the applicability of the semi-emprical scaling law on different HVAC geometries both literature data and new measurement data are considered. Focus is at comparing geometries of high and low pressure loss but also to discuss the differences in other properties, e.g. radiation characteristics. A general noise reference spectrum is determined bya best fit calculation of measurement data including orifice, damper and bend geometries. Air terminal devices at the end of a duct are also evaluated and compared to constrictions inside ducts. The expected accuracy of the suggested model and its challenges as a tool for flow noise prediction of non-rotating components in HVAC systems are discussed.

Abstract [sv]

På grund av ökade energieffektivitetskrav har större fläktar som roterar med lägre hastighet börjat användas i byggnaders ventilationssystem(HVAC). De lägre hastigheterna har minskat ljudnivån från fläkten och ökat betydelsen av strömningsalstrat ljud från andra systemkomponenter, t.ex. spjäll och luftdon. I denna avhandling presenteras en förbättrad prediktionsmodell, utifrån semi-empiriska skalningslagar, för strömningsalstrat ljud i ventilationssystem. Skalningslagarna kan ses som en kombination av generellaljudspektra och strypningens specifika flödesegenskaper, där det senare kan fås från Computational Fluid Dynamics (CFD) simuleringar. Semiempiriska skalningslagar är ett alternativ för att undvika tidskrävandemätningar eller fullt upplösta simuleringar. Ett tillvägagångssätt presenteras här där det generella spektrat, bestämt utifrån experimentell data, kombineras med data från Reynolds Average Navier Stokes (RANS) simuleringar. En prediktionsmodell föreslås där källstyrkan hos dipolkrafterna definieras utifrån rörelsemängd och frekvensskalningen utifrån strypningens tryckfall. För att utvärdera vilka HVAC geometrier som kan ingå i den generella modellen analyseras både resultat från litteraturen samt nya mätningar. Avhandlingsarbetet fokuserar på att jämföra geometrier av högt och lågt tryckfall men också på att diskutera skillnader i andra egenskaper såsom strålningskarakteristik t.ex. genom att jämföra luftdon i slutet av en kanal med strypningar inuti kanalen. Ett generellt ljudspektrum föreslås utifrån en anpassning av mätdata för strypningar, spjäll och böjar. Modellens förväntade noggrannhet och dess utmaningar som prediktionsverktyg för icke-roterande komponenter i ventilationssystem diskuteras.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , v, 46 p.
Series
TRITA-AVE, ISSN 1651-7660 ; 2015:22
Keyword [en]
flow noise, noise prediction, HVAC
Keyword [sv]
flödesalstrat ljud, bullerprediktion, HVAC
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-166201ISBN: 978-91-7595-564-3 (print)OAI: oai:DiVA.org:kth-166201DiVA: diva2:809693
Presentation
2015-05-27, sal Munin, Teknikringen 8, BV, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council Formas, 245-2011-1615
Note

QC 20150518

Available from: 2015-05-18 Created: 2015-05-05 Last updated: 2015-05-18Bibliographically approved
List of papers
1. Prediction model of flow duct constriction noise
Open this publication in new window or tab >>Prediction model of flow duct constriction noise
2014 (English)In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 82, 45-52 p.Article in journal (Refereed) Published
Abstract [en]

The scaling law for aerodynamic dipole type of sound from constrictions in low speed flow ducts by Nelson and Morfey is revisited. A summary of earlier published results using this scaling law is presented together with some new data. Based on this, an effort to find a general scaling law for the sound power for components with both distinct and non-distinct flow separation points are made. Special care is taken to apply the same scaling to all data based on the pressure drop. Results from both rectangular and circular ducts, duct flow velocities from 2 to 120 m/s and sound power measurements made both in ducts and in reverberation chambers are presented. The computed sound power represents the downstream source output in a reflection free duct. In particular for the low frequency plane wave range strong reflections from e.g. openings can affect the sound power output. This is handled by reformulating the Nelson and Morfey model in the form of an active acoustic 2-port. The pressure loss information needed for the semi-empirical scaling law can be gained from CFD simulations. A method using Reynold Average Navier Stokes (RANS) simulations is presented, where the required mesh quality is evaluated and estimation of the dipole source strength via the use of the pressure drop is compared to using the turbulent kinetic energy.

Keyword
Flow noise, Noise prediction, RANS
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-147018 (URN)10.1016/j.apacoust.2014.03.001 (DOI)000336117500007 ()2-s2.0-84897514407 (Scopus ID)
Funder
Formas, 245-2011-1615
Note

QC 20140625

Available from: 2014-06-25 Created: 2014-06-23 Last updated: 2017-12-05Bibliographically approved
2. Revisiting the Nelson-Morfey scaling law for flow noise from duct constrictions
Open this publication in new window or tab >>Revisiting the Nelson-Morfey scaling law for flow noise from duct constrictions
2015 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 357, 233-244 p.Article in journal (Refereed) Published
Abstract [en]

The semi empirical scaling law by Nelson and Morfey [1] predicts the noise generation from constrictions in ducts with low Mach number flows. The results presented here demonstrate that the original model loose accuracy for constrictions of high pressure loss. An extension based on a momentum flux assumption of the dipole forces is suggested and is evaluated against measurement results for orifice geometries of higher pressure loss than earlier evaluated. A prediction model including constrictions at flow duct terminations is also suggested. Improved accuracy for the predictions of the new model are found for orifice geometries of both high and low pressure loss inside and at end of ducts. The extended model is finally evaluated by measurementson a regular ventilation air terminal device.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-166200 (URN)10.1016/j.jsv.2015.06.019 (DOI)000360965200015 ()2-s2.0-84940889140 (Scopus ID)
Funder
Swedish Research Council Formas, 245-2011-1615
Note

Updated from manuscript to article.

QC 20151009

Available from: 2015-05-05 Created: 2015-05-05 Last updated: 2017-12-04Bibliographically approved

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Licentiate Thesis(7344 kB)533 downloads
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Kårekull, Oscar

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