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Lim, S. M., Dahlkild, A. & Mihaescu, M. (2019). Influence of Upstream Exhaust Manifold on Pulsatile Turbocharger Turbine Performance. Paper presented at 141(6), 061010. Journal of engineering for gas turbines and power, 141(6)
Open this publication in new window or tab >>Influence of Upstream Exhaust Manifold on Pulsatile Turbocharger Turbine Performance
2019 (English)In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 141, no 6Article in journal (Refereed) Published
Abstract [en]

This research was primary motivated by limited efforts to understand the effects of secondary flow and flow unsteadiness on the heat transfer and the performance of a turbocharger turbine subjected to pulsatile flow. In this study, we aimed to investigate the influence of exhaust manifold on the flow physics and the performance of its downstream components, including the effects on heat transfer, under engine-like pulsatile flow conditions. Based on the predicted results by detached eddy simulation (DES), qualitative and quantitative flow fields analyses in the scroll and the rotor's inlet were performed, in addition to the quantification of turbine performance by using the flow exergy methodology. With the specified geometry configuration and exhaust valve strategy, our study showed that (1) the exhaust manifold influences the flow field and the heat transfer in the scroll significantly and (2) although the exhaust gas blow-down disturbs the relative flow angle at rotor inlet, the consequence on the turbine power is relatively small.

Keywords
turbocharger turbine, engine-like pulsatile flow, heat transfer, exergy, DES
National Category
Mechanical Engineering Fluid Mechanics and Acoustics Vehicle Engineering
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-244665 (URN)10.1115/1.4042301 (DOI)000468915800011 ()2-s2.0-85061841259 (Scopus ID)
Conference
141(6), 061010
Funder
Swedish Energy Agency, 33834-3
Note

QC 20190226

Available from: 2019-02-22 Created: 2019-02-22 Last updated: 2019-10-24Bibliographically approved
Schickhofer, L., Dahlkild, A. & Mihaescu, M. (2019). On direct aeroacoustics calculations of the vocal tract. In: Direct and Large-Eddy Simulation XI, ERCOFTAC Series: . Paper presented at the 11th workshop on Direct and Large Eddy Simulation (DLES),Pisa, Italy in May 2017. , 25
Open this publication in new window or tab >>On direct aeroacoustics calculations of the vocal tract
2019 (English)In: Direct and Large-Eddy Simulation XI, ERCOFTAC Series, 2019, Vol. 25Conference paper, Published paper (Refereed)
Abstract [en]

Voice production and the verbal expression through speech are crucial components of human communication. The human voice is not just conveying information directly through words, but also indirectly as paralinguistic information such as the speaker's emotional state through tonality.

As such, voice is generated through a two-part process: First, a source signal is produced by the vocal folds that are pulsating the lung pressure and volumetric flow rate in a particular frequency through periodic opening and closing. Second, the vocal tract causes an attenuation or amplification of this source signal at certain frequencies depending on its specific shape. The voice generation process can therefore be described by a source-filter model with the vocal folds acting as the source and the vocal tract as an acoustic filter. Thus, we are able to produce different vowels and sounds as we manipulate the vocal tract during phonation.

However, the ability to speak can be compromised due to clinical conditions affecting the opening between the vocal folds (i.e. glottis) or the vocal tract. Certain voice disorders such as partial or total vocal fold paralysis and laryngeal cancer are known to affect the source signal and its waveform considerably.

Nevertheless, the actual cause-effect relations between physiological changes in the vocal tract and the acoustic pressure in the far field are unclear. In acoustics, the far field is defined as the region away from the source, where sound pressure levels follow the inverse square law and show a decrease of approximately 6 dB for each doubling of the distance from the source.

An additional factor in voice production is the shedding of intraglottal vortical structures. The sound output generated by vortices becomes important in cases of incomplete glottal closure or paralysed vocal folds. In this study, the acoustic signal generated through speech is computed directly as pressure fluctuations resulting from unsteady large eddy simulations, applied to magnetic resonance imaging (MRI) data. Thus, a time-resolved solution for the acoustic pressure in the upper airways is achieved, contributing to the knowledge of cause-effect relations in phonation and opening up new therapeutic options for vocal tract and airway disorders by the use of computational fluid dynamics.

Series
ERCOFTAC Series ; 25
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-240551 (URN)978-3-030-04914-0 (ISBN)
Conference
the 11th workshop on Direct and Large Eddy Simulation (DLES),Pisa, Italy in May 2017
Note

QC 20190215

Available from: 2018-12-19 Created: 2018-12-19 Last updated: 2019-02-15Bibliographically approved
Lim, S. M., Dahlkild, A. & Mihaescu, M. (2018). Aerothermodynamics and Exergy Analysis in Radial Turbine With Heat Transfer. Journal of turbomachinery, 140(9), Article ID 091007.
Open this publication in new window or tab >>Aerothermodynamics and Exergy Analysis in Radial Turbine With Heat Transfer
2018 (English)In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 140, no 9, article id 091007Article in journal (Refereed) Published
Abstract [en]

This study was motivated by the difficulties to assess the aerothermodynamic effects of heat transfer on the performance of turbocharger turbine by only looking at the global performance parameters, and by the lack of efforts to quantify the physical mechanisms associated with heat transfer. In this study, we aimed to investigate the sensitivity of performance to heat loss, to quantify the aerothermodynamic mechanisms associated with heat transfer and to study the available energy utilization by a turbocharger turbine. Exergy analysis was performed based on the predicted three-dimensional flow field by detached eddy simulation (DES). Our study showed that at a specified mass flow rate, (1) pressure ratio drop is less sensitive to heat loss as compared to turbine power reduction, (2) turbine power drop due to heat loss is relatively insignificant as compared to the exergy lost via heat transfer and thermal irreversibilities, and (3) a single-stage turbine is not an effective machine to harvest all the available exhaust energy in the system.

Place, publisher, year, edition, pages
ASME Press, 2018
Keywords
Radial turbine, Detached Eddy Simulation, Exergy analysis, Heat loss
National Category
Engineering and Technology Mechanical Engineering Fluid Mechanics and Acoustics Vehicle Engineering
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-235796 (URN)10.1115/1.4040852 (DOI)000447191900007 ()2-s2.0-85053279860 (Scopus ID)
Funder
Swedish Energy Agency, 33834-3
Note

QC 20181009

Available from: 2018-10-04 Created: 2018-10-04 Last updated: 2018-11-14Bibliographically approved
Lim, S. M., Dahlkild, A. & Mihaescu, M. (2018). Aerothermodynamics and exergy analysis of a turbocharger radial turbine integrated with exhaust manifold. In: Institution of Mechanical Engineers - 13th International Conference on Turbochargers and Turbocharging 2018: . Paper presented at 13th International Conference on Turbochargers and Turbocharging, Twickenham Stadium, London 16 May 2018 - 17 May 2018.
Open this publication in new window or tab >>Aerothermodynamics and exergy analysis of a turbocharger radial turbine integrated with exhaust manifold
2018 (English)In: Institution of Mechanical Engineers - 13th International Conference on Turbochargers and Turbocharging 2018, 2018Conference paper, Published paper (Refereed)
Abstract [en]

Large temperature gradients are associated with automotive turbocharger and thus the turbine experiences significant heat loss. Currently, the investigation of aerothermodynamic effects as a result of heat loss in turbine is commonly done by looking at the global performance parameters, i.e. pressure ratio and efficiency. This study aims to investigate the aerothermodynamic effects of heat transfer on a radial turbine operating under engine-like pulsating flow condition by identifying and quantifying the loss mechanisms via an exergy-based method using Detached Eddy Simulation data. Major findings with this study are: 1) Although exergy lost via heat transfer and internal irreversibilities could be as much as the turbine power, the drop of turbine power is only 4% as compared to an adiabatic turbine;2) Only about 12% of the available exhaust energy is extracted by the investigated turbine.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-238831 (URN)2-s2.0-85064985710 (Scopus ID)
Conference
13th International Conference on Turbochargers and Turbocharging, Twickenham Stadium, London 16 May 2018 - 17 May 2018
Note

QC 20181113

Available from: 2018-11-12 Created: 2018-11-12 Last updated: 2019-10-28Bibliographically approved
Lim, S. M., Dahlkild, A. & Mihaescu, M. (2018). Influence of upstream geometry on pulsatile turbocharger turbine performance. Shyang Maw Lim
Open this publication in new window or tab >>Influence of upstream geometry on pulsatile turbocharger turbine performance
2018 (English)Report (Other academic)
Abstract [en]

This research was primary motivated by limited efforts to understand the effects of secondary flow and flow unsteadiness on the heat transfer and the performance of a turbocharger turbine subjected to pulsatile flow. In this study, we aimed to investigate the influence of exhaust manifold on the flow physics and the performance of its downstream components, including the effects on heat transfer, under engine-like pulsatile flow conditions. Based on the predicted results by Detached Eddy Simulation (DES), qualitative and quantitative flow fields analyses in the scroll and the rotor’s inlet were performed, in addition to the quantification of turbine performance by using the flow exergy methodology. With the specified geometry configuration and exhaust valve strategy, our study showed that 1) The exhaust manifold influences the flow field and the heat transfer in the scroll significantly, and 2) Although the relative inflow angle at the rotor’s inlet is significantly affected by the initial exhaust gas blow down from the exhaust manifold, the consequence on the turbine power is relatively small.

Place, publisher, year, edition, pages
Shyang Maw Lim, 2018
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-238852 (URN)
Note

QC 20181113

Available from: 2018-11-12 Created: 2018-11-12 Last updated: 2018-11-14Bibliographically approved
Lim, S. M., Dahlkild, A. & Mihaescu, M. (2018). Influence of upstream geometry on pulsatile turbocharger turbine performance. In: Microturbines, Turbochargers, and Small Turbomachines; Steam Turbines: . Paper presented at ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, GT 2018; Oslo; Norway; 11 June 2018 through 15 June 2018. ASME Press, 8
Open this publication in new window or tab >>Influence of upstream geometry on pulsatile turbocharger turbine performance
2018 (English)In: Microturbines, Turbochargers, and Small Turbomachines; Steam Turbines, ASME Press, 2018, Vol. 8Conference paper, Published paper (Refereed)
Abstract [en]

Unlike conventional turbomachinery, an automotive turbocharger's turbine is operated under unsteady hot and pulsatile flow due to the inherent nature of reciprocating engine. Although the turbine is integrated with exhaust manifold in real application, some experiments and numerical studies ignore its presence. In this study, we aimed to investigate the effects of upstream complex exhaust manifold on the prediction of pulse flow turbine performance via Detached Eddy Simulation (DES). Heat transfer was incorporated and the exergy based approach was used to quantify the heat transfer associated losses. Our primary results showed that under the investigated turbine stage, although the presence of exhaust manifold influences the prediction of heat transfer and internal irreversibilities in the scroll significantly, it does not significantly affect the prediction of turbine power, heat transfer and irreversibilities at the downstream components.

Place, publisher, year, edition, pages
ASME Press, 2018
Series
Proceedings of the ASME Turbo Expo ; 8
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-238345 (URN)10.1115/GT2018-76706 (DOI)000457071200021 ()2-s2.0-85053896779 (Scopus ID)9780791851173 (ISBN)
Conference
ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, GT 2018; Oslo; Norway; 11 June 2018 through 15 June 2018
Note

QC 20181119

Available from: 2018-11-19 Created: 2018-11-19 Last updated: 2019-12-12Bibliographically approved
Schickhofer, L., Dahlkild, A. & Mihaescu, M. (2017). Influence of changes of the glottal waveform on vowel production. In: Proceedings of Meetings on Acoustics (POMA), Acoustical Society of America, Paper ICA2016-586, 2017: . Paper presented at International Congress on Acoustics, Acoustical Society of America.
Open this publication in new window or tab >>Influence of changes of the glottal waveform on vowel production
2017 (English)In: Proceedings of Meetings on Acoustics (POMA), Acoustical Society of America, Paper ICA2016-586, 2017, 2017Conference paper, Published paper (Refereed)
Abstract [en]

Conditions of the vocal folds and upper airways can directly influence the fundamental frequency of the periodic movement of the glottis as well as the waveform of the source signal. This could further impair a patient's ability to excite resonances of the vocal tract and generate vowels. In this study, the Rosenberg model for the glottal pulse is applied to numerically investigate the propagation of the voice source signal from the glottis through a static vocal tract model. The geometries of the vocal tract are based on magnetic resonance imaging data for the different vowel pronunciations of a healthy male subject. For the computation of the pressure fluctuations and the associated distribution of frequency peaks as a result of the modulation through the vocal tract, direct compressible flow simulations are carried out by using a finite volume solver. The results are compared with the solution of a wave reflection analogue based on the area functions extracted from the same geometries and good agreement is reached. The effect of variations of glottal closure and fundamental frequency of the standard Rosenberg waveform on the computed acoustic signal is investigated. Thus, an estimation of the impact of glottal diseases on the ability of vowel production is attempted.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-240550 (URN)10.1121/2.0000413 (DOI)
Conference
International Congress on Acoustics, Acoustical Society of America
Note

QC 20190129

Available from: 2018-12-19 Created: 2018-12-19 Last updated: 2019-01-29Bibliographically approved
Schickhofer, L., Dahlkild, A. & Mihaescu, M. (2016). Aeroacoustics of an elastic element in unsteady flow of low Reynolds numbers. In: AIAA Technical Paper 2016-2700, 22nd AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2016: . Paper presented at 22nd AIAA/CEAS Aeroacoustics Conference, 2016, Lyon, France, 30 May 2016 through 1 June 2016.
Open this publication in new window or tab >>Aeroacoustics of an elastic element in unsteady flow of low Reynolds numbers
2016 (English)In: AIAA Technical Paper 2016-2700, 22nd AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2016, 2016Conference paper, Published paper (Refereed)
Abstract [en]

Vibrations of elastic structures are a common occurrence in numerous fields of engineering such as aeronautics, aerodynamics, civil engineering, and biomechanics. Particular e ort is dedicated to aeroacoustics of elements that are excited to oscillatory behaviour due to fluid instabilities. The current study is concerned with the numerical investigation of the flow-induced vibrations of a flexible, beam-like element in crossflow at low Reynolds numbers of Re = 100 − 1000 by means of fluid-structure interaction simulations. The aeroa-coustics in the near field are assessed with direct computation of the compressible airflow. Additionally, an acoustic analogy is applied, characterising the acoustic sources and the corresponding sound propagation. At low Reynolds numbers and high elastic moduli the dipole source produces the highest pressure perturbation in the near field. At higher Reynolds numbers and low elastic moduli, however, the monopole source due to structural vibrations becomes the important sound generating mechanism.

National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-194604 (URN)10.2514/6.2016-2700 (DOI)2-s2.0-85057294256 (Scopus ID)9781624103865 (ISBN)
Conference
22nd AIAA/CEAS Aeroacoustics Conference, 2016, Lyon, France, 30 May 2016 through 1 June 2016
Note

 QC 20161102

Available from: 2016-11-02 Created: 2016-10-31 Last updated: 2019-08-21Bibliographically approved
Lim, S. M., Dahlkild, A. & Mihaescu, M. (2016). Wall Treatment Effects on the Heat Transfer in a Radial Turbine Turbocharger. In: Springer Proceedings in Physics: . Paper presented at 5th International Conference on Jets, Wakes and Separated Flows, ICJWSF2015, 15 June 2015 through 18 June 2015 (pp. 439-447). Springer Science+Business Media B.V.
Open this publication in new window or tab >>Wall Treatment Effects on the Heat Transfer in a Radial Turbine Turbocharger
2016 (English)In: Springer Proceedings in Physics, Springer Science+Business Media B.V., 2016, p. 439-447Conference paper, Published paper (Refereed)
Abstract [en]

Contradicting results about heat transfer effects on the performance of turbine turbocharger motivated this study. It was aimed to assess the effects that the wall treatment in a numerical sense has on the performance of a radial turbine of automotive turbocharger operating under a continuous flow condition. Adiabatic and non-adiabatic conditions were analyzed by using Unsteady Reynolds Averaged Navier-Stokes (URANS), Large Eddy Simulations (LES) and Detached Eddy Simulations (DES) approaches. When considering heat transfer, heat transfer loss at various locations is highly dependent on the near-wall modelling approach employed. Development of thermal boundary layer in the upstream region of turbine affects how the gas is convected in the downstream components, such as the scroll and the rotor. As long as the deviation in predicting thermal boundary layer does not affect the prediction of gas temperature at the inlet and outlet of the rotor, the difference in turbine power prediction by different near-wall modelling approaches was found to be small.

Place, publisher, year, edition, pages
Springer Science+Business Media B.V., 2016
Keywords
Boundary layers, Compressors, Forecasting, Large eddy simulation, Navier Stokes equations, Superchargers, Turbine components, Turbines, Turbomachinery, Wakes, Automotive turbochargers, Detached eddy simulations, Downstream components, Heat transfer effects, Heat transfer loss, Non-adiabatic conditions, Thermal boundary layer, Unsteady reynolds-averaged navier-stokes, Heat transfer
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-195489 (URN)10.1007/978-3-319-30602-5_55 (DOI)000387431400055 ()2-s2.0-84978943601 (Scopus ID)9783319306001 (ISBN)
Conference
5th International Conference on Jets, Wakes and Separated Flows, ICJWSF2015, 15 June 2015 through 18 June 2015
Note

QC 20161125

Available from: 2016-11-25 Created: 2016-11-03 Last updated: 2018-11-12Bibliographically approved
Zhang, F., Dahlkild, A. A., Gustavsson, K. & Lundell, F. (2014). Near-Wall Convection in a Sedimenting Suspension of Fibers. AIChE Journal, 60(12), 4253-4265
Open this publication in new window or tab >>Near-Wall Convection in a Sedimenting Suspension of Fibers
2014 (English)In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 60, no 12, p. 4253-4265Article in journal (Refereed) Published
Abstract [en]

The sedimentation of a fiber suspension near a vertical wall is investigated numerically. Initially, the near-wall convection is an upward backflow, which originates from the combined effects of the steric-depleted layer and a hydrodynamically depleted region near the wall. The formation of the hydrodynamically depleted region is elucidated by a convection-diffusion investigation, in which fibers are classified according to the different directions in which they drift. For fibers with sufficiently large aspect ratio, the initial near-wall backflow keeps growing. However, the backflow reverses to downward flow at later times if the aspect ratio is small. This is due to the fiber-wall interactions which rotate fibers to such angles that make fibers drift away from the wall, inducing a dense region and a correspondingly downward flow outside the initial backflow. Moreover, the steric-depleted boundary condition is of secondary importance in the generation and evolution of the near-wall convection.

Keywords
fibers, fluid mechanics, settling, sedimentation, multiphase flow
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-158802 (URN)10.1002/aic.14576 (DOI)000345232900023 ()2-s2.0-84921843129 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20150204

Available from: 2015-02-04 Created: 2015-01-12 Last updated: 2017-12-05Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-2906-9306

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