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Schickhofer, L., Malinen, J. & Mihaescu, M. (2019). Compressible flow simulations of phonation using realistic vocal tract geometries. Journal of the Acoustical Society of America
Open this publication in new window or tab >>Compressible flow simulations of phonation using realistic vocal tract geometries
2019 (English)In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524Article in journal (Refereed) Submitted
Abstract [en]

Voiced speech consists mainly of the source signal that is frequency-weighted by the acoustic filtering of the upper airways and vortex-induced sound through perturbation in the flow field. This study investigates the flow instabilities leading to vortex shedding and the importance of coherent structures in the supraglottal region downstream of the vocal folds for the far-field sound signal. Large eddy simulations of the compressible airflow through the glottal contriction are performed in realistic geometries obtained from three-dimensional magnetic resonance imaging data. Intermittent flow separation through the glottis is shown to introduce unsteady surface pressure through impingement of vortices. Additionally, dominant flow instabilities develop in the shear layer associated with the glottal jet. The aerodynamic perturbations in the near field and the acoustic signal in the far field is examined by means of spatial and temporal Fourier analysis. Furthermore, the acoustic sources due to the unsteady supraglottal flow are identified with the aid of surface spectra and critical regions of amplification of the dominant frequencies of the investigated vowel geometries are identified.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-240552 (URN)
Note

QC 20190119

Available from: 2018-12-19 Created: 2018-12-19 Last updated: 2019-01-29Bibliographically approved
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), Article ID GTP-18-1704.
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 6, article id GTP-18-1704Article 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)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: 2019-03-18Bibliographically 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
Pietroniro, A. G., Mihaescu, M., Åbom, M. & Knutsson, M. (2018). A Steady-State Based Investigation of Automotive Turbocharger Compressor Noise. In: : . Paper presented at SAE 10th International Styrian Noise, Vibration and Harshness Congress: The European Automotive Noise Conference, SNVH 2018, Congress GrazSparkassenplatz 1Graz, Austria, 20 June 2018 through 22 June 2018. SAE International, 2018-June(June)
Open this publication in new window or tab >>A Steady-State Based Investigation of Automotive Turbocharger Compressor Noise
2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The challenging problem of noise generation and propagation in automotive turbocharging systems is of real interest from both scientific and practical points of view. Robust and fast steady-state fluid flow calculations, complemented by acoustic analogies can represent valuable tools to be used for a quick assessment of the problem during e.g. design phase, and a starting point for more in-depth future unsteady calculations. Thus, as a part of the initial phase of a long-term project, a steady-state Reynolds Averaged Navier-Stokes (RANS) flow analysis is carried out for a specific automotive turbocharger compressor geometry. Acoustic data are extracted by means of aeroacoustics models available within the framework of the STAR-CCM+ solver (i.e. Curle and Proudman acoustic analogies, respectively). This part of the work focuses on the discussion and comparison of the aeroacoustic models, and their suitability towards predicting flow and acoustics trends corresponding to the operating conditions investigated. However, given the unsteady nature of acoustics, the project will have to develop towards an investigation of the problem using more expensive, but more accurate, Large Eddy Simulation (LES) calculations. An entire compressor map with 80 operating conditions was simulated, yielding trends in the behaviour of the performance parameters for the analysed compressor. Detailed results calculated on the same compressor speed-line for one design and one off-design operating conditions are presented in terms of time-averaged pressure coefficient, Mach number, and acoustic power distributions. A total acoustic power map has been generated based on the outcome from the Curle and Proudman acoustic models, giving an indication of the noisiest operating conditions.

Place, publisher, year, edition, pages
SAE International, 2018
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-238199 (URN)10.4271/2018-01-1528 (DOI)2-s2.0-85050556716 (Scopus ID)
Conference
SAE 10th International Styrian Noise, Vibration and Harshness Congress: The European Automotive Noise Conference, SNVH 2018, Congress GrazSparkassenplatz 1Graz, Austria, 20 June 2018 through 22 June 2018
Note

QC 20181116

Available from: 2018-11-16 Created: 2018-11-16 Last updated: 2019-04-24
Sundström, E., Semlitsch, B. & Mihaescu, M. (2018). Acoustic signature of flow instabilities in radial compressors. Journal of Sound and Vibration, 434, 221-236
Open this publication in new window or tab >>Acoustic signature of flow instabilities in radial compressors
2018 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 434, p. 221-236Article in journal (Refereed) Published
Abstract [en]

Rotating stall and surge are flow instabilities contributing to the acoustic noise generated in centrifugal compressors at low mass flow rates. Their acoustic generation mechanisms are exposed employing compressible Large Eddy Simulations (LES). The LES data are used for calculating the dominant acoustic sources emerging at low mass flow rates. They give the inhomogeneous character of the Ffowcs Williams and Hawkings (FW-H) wave equation. The blade loading term associated with the unsteady pressure loads developed on solid surfaces (dipole in character) is found to be the major contributor to the aerodynamically generated noise at low mass flow rates. The acoustic source due to the velocity variations and compressibility effects (quadrupole in character) as well as the acoustic source caused by the displacement of the fluid due to the accelerations of the solid surfaces (monopole in character) were found to be not as dominant. We show that the acoustic source associated with surge is generated by the pressure oscillation, which is governed by the tip leakage flow. The vortical structures of rotating stall are interacting with the impeller. These manipulate the flow incidence angles and cause thereby unsteady blade loading towards the discharge. A low-pressure sink between 4 and 6 o'clock causes a halving of the perturbation frequencies at low mass flow rates operating conditions. From two point space-time cross correlation analysis based on circumferential velocity in the diffuser it was found that the rotating stall cell propagation speed increases locally in the low pressure zone under the volute tongue. It was also found that rotating stall can coexist with surge operating condition, but the feature is then seen to operate over a broader frequency interval.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Large Eddy Simulations, Rotating stall, Surge, Acoustics source, Centrifugal compressor
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-233576 (URN)10.1016/j.jsv.2018.07.040 (DOI)000444001700013 ()2-s2.0-85051117612 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20180830

Available from: 2018-08-25 Created: 2018-08-25 Last updated: 2018-09-27Bibliographically 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: : . 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)Conference 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)
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: 2018-11-14Bibliographically approved
Chen, S., Gojon, R. & Mihaescu, M. (2018). High-Temperature Effects on Aerodynamic and Acoustic Characteristics of a Rectangular Supersonic Jet. In: AIAA (Ed.), AIAA/CEAS Aeroacoustics Conference, AIAA AVIATION Forum, 2018: . Paper presented at AIAA/CEAS Aeroacoustics Conference, AIAA AVIATION Forum, (AIAA 2018-3303). , Article ID 3303.
Open this publication in new window or tab >>High-Temperature Effects on Aerodynamic and Acoustic Characteristics of a Rectangular Supersonic Jet
2018 (English)In: AIAA/CEAS Aeroacoustics Conference, AIAA AVIATION Forum, 2018 / [ed] AIAA, 2018, article id 3303Conference paper, Published paper (Refereed)
Abstract [en]

Implicit large-eddy simulations (LES) are performed in this work to study the flow field and acous-tic characteristics of a rectangular supersonic jet. The focus is to investigate the high-temperatureeffects, i.e. when the jet total temperature is as high as 2100 K. Four cases with a jet temperatureratio(TR) of 1.0, 2.0, 4.0 and 7.0 are investigated. The rectangular nozzle selected for this study hasan aspect ratio of 2. The jets are overexpanded, with a series of shock cells in the jet core region.An artificial dissipation mechanism is used to damp the numerical oscillation and to represent theeffect of small-scale turbulence. The temperature-dependent thermal properties of air within thehigh-temperature regime are also considered by using the chemical equilibrium assumption. Thenumerical results show that the high temperature significantly increases the jet velocity and acousticMach number, although the jet Mach number is maintained roughly the same. Meanwhile, the lengthof the jet core region of the hot jet (TR = 7.0) is found to be reduced by around 30 %, compared tothe cold jet. The convection velocity and acoustic convection Mach number in the shear layer are alsoobserved to be increased when the jet temperature is high. The elevated acoustic convection Machnumber directly leads to a strong Mach wave radiation, and the crackle noise component has beenidentified by the pressure skewness and kurtosis factors. The Strouhal number of the screech tone isfound to be decreased slightly, and good agreements between the numerical results and the theoreticalanalysis are observed. Moreover, the sound pressure levels (SPL) associated with turbulent mixing,screech, Mach wave radiation, and Broadband shock associated noise are all found to be amplified indifferent levels for the hot jets. In the far field, the SPL is strongly increased by the high-temperatureeffect. Higher SPL is notably observed in the Mach wave radiation directions.

Keywords
Large Eddy Simulation, Supersonic rectangular jets, Aeroacoustics, Temperature effects
National Category
Fluid Mechanics and Acoustics Aerospace Engineering
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-235799 (URN)10.2514/6.2018-3303 (DOI)2-s2.0-85051292277 (Scopus ID)978-1-62410-560-9 (ISBN)
Conference
AIAA/CEAS Aeroacoustics Conference, AIAA AVIATION Forum, (AIAA 2018-3303)
Note

QC 20181010

QC 20181017

Available from: 2018-10-04 Created: 2018-10-04 Last updated: 2018-10-17Bibliographically 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/GT201876706 (DOI)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: 2018-11-19Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-7330-6965

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