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Publications (10 of 87) Show all publications
Kerres, B., Sanz, S., Sundström, E. & Mihaescu, M. (2017). A Comparison of Performance Predictions between 1D Models and Numerical Data for a Turbocharger Compressor. In: Proceedings of 12th European Conference on Turbomachinery Fluid dynamics and Thermodynamics ETC12, April 3-7, Stockholm, Sweden: . Paper presented at 12th European Conference on Turbomachinery Fluid dynamics and Thermodynamics ETC12, April 3-7, Stockholm, Sweden. KTH Royal Institute of Technology.
Open this publication in new window or tab >>A Comparison of Performance Predictions between 1D Models and Numerical Data for a Turbocharger Compressor
2017 (English)In: Proceedings of 12th European Conference on Turbomachinery Fluid dynamics and Thermodynamics ETC12, April 3-7, Stockholm, Sweden, KTH Royal Institute of Technology, 2017Conference paper, Published paper (Refereed)
Abstract [en]

Compressor performance prediction models, based on integral conservation of mass, momentum and energy with empirical loss terms, are important tools in early design stages. Two such models from literature are compared to numerical results for an automotive turbocharger radial compressor with a vaneless diffuser and a volute. Results show that these models are less accurate than fully three-dimensional numerical RANS CFD calculations at low impeller speeds and choke, but can compete at high impeller speeds. Of the two impeller models, one gives a more accurate prediction than the other. The diffuser and volute models investigated here show large differences to the CFD calculations at off-design conditions. A comparison of the impeller loss terms to CFD entropy increase indicates also possibilities for improvement in the impeller models.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017
Keyword
Radial compressor, 1D model, RANS, performance prediction
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-206518 (URN)2-s2.0-85021822532 (Scopus ID)
Conference
12th European Conference on Turbomachinery Fluid dynamics and Thermodynamics ETC12, April 3-7, Stockholm, Sweden
Funder
Swedish Energy Agency
Note

QC 20170508

Available from: 2017-05-04 Created: 2017-05-04 Last updated: 2017-08-15Bibliographically approved
Schickhofer, L., Dahlkild, A. & Mihaescu, M. (2016). Aeroacoustics of an elastic element in unsteady flow of low reynolds numbers. In: 22nd AIAA/CEAS Aeroacoustics Conference, 2016: . Paper presented at 22nd AIAA/CEAS Aeroacoustics Conference, 2016, 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: 22nd AIAA/CEAS Aeroacoustics Conference, 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. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

Keyword
Acoustic wave propagation, Acoustics, Elastic moduli, Elasticity, Fluid structure interaction, Reynolds number, Structural dynamics, Flow induced vibrations, Generating mechanism, High elastic modulus, Low elastic modulus, Low Reynolds number, Numerical investigations, Pressure perturbation, Structural vibrations, Aeroacoustics
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-194604 (URN)2-s2.0-84982943380 (Scopus ID)9781624103865 (ISBN)
Conference
22nd AIAA/CEAS Aeroacoustics Conference, 2016, 30 May 2016 through 1 June 2016
Note

Conference Paper. QC 20161102

Available from: 2016-11-02 Created: 2016-10-31 Last updated: 2016-11-02Bibliographically approved
Kerres, B., Nair, V., Cronhjort, A. & Mihaescu, M. (2016). Analysis of the Turbocharger Compressor Surge Margin Using a Hurst-Exponent-based Criterion. SAE International Journal of Engines, 9(3).
Open this publication in new window or tab >>Analysis of the Turbocharger Compressor Surge Margin Using a Hurst-Exponent-based Criterion
2016 (English)In: SAE International Journal of Engines, ISSN 1946-3936, E-ISSN 1946-3944, Vol. 9, no 3Article in journal (Refereed) Published
Abstract [en]

Turbocharger compressors are limited in their operating range at low mass flows by compressor surge, thus restricting internal combustion engine operation at low engine speeds and high mean effective pressures. Since the exact location of the surge line in the compressor map depends on the whole gas exchange system, a safety margin towards surge must be provided. Accurate early surge detection could reduce this margin. During surge, the compressor outlet pressure fluctuates periodically. The Hurst exponent of the compressor outlet pressure is applied in this paper as an indicator to evaluate how close to the surge limit the compressor operates. It is a measure of the time-series memory that approaches zero for anti-persistence of the time series. That is, a Hurst exponent close to zero means a high statistical preference that a high value is followed by a low value, as during surge. Maps of a passenger-car sized turbocharger compressor with inlet geometries that result in different surge lines are measured on a cold gas stand. It is demonstrated that the Hurst exponent in fact decreases as the compressor moves towards surge, and that a constant value of the Hurst exponent can be used as a threshold for stable operation. Transient pressure signals of the compressor entering surge are analyzed in order to evaluate the time lag until surge can be detected using the Hurst exponent. Two surge cycles are usually needed to detect unstable operation. However, since the amplitude of these oscillations is relatively small for the first cycles, detection is possible before the oscillations grow into deep surge.

Place, publisher, year, edition, pages
SAE International, 2016
Keyword
Centrifugal compressor, surge analysis, surge detection, surge margins, Turbocharging, Hurst exponent
National Category
Mechanical Engineering
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-185757 (URN)10.4271/2016-01-1027 (DOI)2-s2.0-84975230385 (Scopus ID)
Projects
Compressor Off-design Operation- CCGEx
Funder
Swedish Energy Agency
Note

QC 20160429

Available from: 2016-04-26 Created: 2016-04-26 Last updated: 2017-11-30Bibliographically approved
Sundström, E., Kerres, B. & Mihaescu, M. (2016). Evaluation of centrifrugal compressor performance models using large eddy simulation data. In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2016, VOL 2C. Paper presented at ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition, GT 2016; Seoul; South Korea; 13 June 2016 through 17 June 2016. ASME Press.
Open this publication in new window or tab >>Evaluation of centrifrugal compressor performance models using large eddy simulation data
2016 (English)In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2016, VOL 2C, ASME Press, 2016Conference paper, Published paper (Refereed)
Abstract [en]

Zero-dimensional (OD) compressor performance models, which consist of several sub-models for different loss terms, are useful tools in early design stages. In this paper, one typical model for centrifugal compressors is evaluated by comparing the loss-terms predicted by the model to data extracted from experimentally validated Large-Eddy-Simulation. The simulations were run on a truck-sized turbocharger compressor with a ported shroud and a vaneless diffuser. Four operating points are considered: One mass flow at design conditions and one mass flow close to surge, on two speedlines. The performance prediction models evaluated are impeller incidence loss, impeller skin friction loss, diffuser skin friction loss, and the tip clearance loss. Results show that the total losses are well-predicted by the model at design conditions. Friction losses are approximately independent of mass flow in the LES data, while the OD model assumes a quadratic increase. The assumption of constant tip clearance loss is validated by the LES data, and the impeller incidence loss model also fits the data well. Due to the ported shroud, most of the losses as calculated by entropy increase occur through isobaric mixing at the impeller inlet.

Place, publisher, year, edition, pages
ASME Press, 2016
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-199014 (URN)10.1115/GT2016-57169 (DOI)000387297500040 ()2-s2.0-84991738228 (Scopus ID)
Conference
ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition, GT 2016; Seoul; South Korea; 13 June 2016 through 17 June 2016
Note

QC 20170119

Available from: 2017-01-19 Created: 2016-12-22 Last updated: 2017-11-17Bibliographically approved
Kerres, B., Cronhjort, A. & Mihaescu, M. (2016). Experimental investigation of upstream installation effects on the turbocharger compressor map. In: The 12th International Conference on Turbochargers and Turbocharging, London, UK, 17-18 May, 2016: . Paper presented at The 12th International Conference on Turbochargers and Turbocharging, London, UK, 17-18 May, 2016. .
Open this publication in new window or tab >>Experimental investigation of upstream installation effects on the turbocharger compressor map
2016 (English)In: The 12th International Conference on Turbochargers and Turbocharging, London, UK, 17-18 May, 2016, 2016Conference paper, Published paper (Refereed)
Abstract [en]

This paper experimentally investigates the effects of an upstream bended pipe on the compressor speedline slopes and surge line. Different orientation angles for the incoming bended pipe relative to the compressor scroll are investigated. The tests were carried out on a cold gas stand on a passenger car sized turbocharger. A bended pipe upstream of the compressor leads to an increase of the surge margin. This effect does not depend on the orientation of the bend. Comparisons with a straight inlet with artificially generated pressure losses indicate that the increase in operating range is an effect of the pressure losses generated in the bend.

Keyword
Turbochargers, Centrifugal Compressors, Compressor Surge
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-191296 (URN)978-0-9572374-7-6 (ISBN)
External cooperation:
Conference
The 12th International Conference on Turbochargers and Turbocharging, London, UK, 17-18 May, 2016
Note

QC 20160829

Available from: 2016-08-26 Created: 2016-08-26 Last updated: 2017-05-08Bibliographically approved
Schickhofer, L., Semlitsch, B. & Mihaescu, M. (2016). Numerical Flow Simulations of a Flexible Plate Attached to an Obstacle in Crossflow. In: : . Paper presented at International Conference on Jets, Wakes and Separated Flows ( ICJWSF2015). Springer.
Open this publication in new window or tab >>Numerical Flow Simulations of a Flexible Plate Attached to an Obstacle in Crossflow
2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

For biomedical applications with relevance to the human upper respiratory tract, the knowledge of the tissue behavior when exposed to a particular flow field would be desired. Moreover, there is of importance to quantify how the tissue properties affects the biomechanics of obstruction. Since in-vivo measurements are often not possible or inappropriate, this is assessed computationally and usually using simplified/idealized geometries.

The present work is devoted to analyze a fluid-structure interaction scenario relevant to snoring and Obstructive Sleep Apnea Syndrome (OSAS). The uncertainty of the solution to the most influential parameters will be assessed, with the aim of quantifying the interplay between the most relevant parameters responsible for tissue self-excitation and obstruction dynamics. A statistical description of the behavior shall be developed. The tissue responsible for snoring in sleep apnea patients (the soft palate) is mimicked in this numerical study by a flexible thin plate anchored to an obstacle. The fluid-structure interaction problem is simulated computationally for several configurations in order to quantify the sensitivity of the investigation parameters onto the flow-field development.

Place, publisher, year, edition, pages
Springer, 2016
Series
Springer Proceedings in Physics, ISSN 0930-8989 ; 185
Keyword
Snoring
National Category
Fluid Mechanics and Acoustics
Research subject
Biological Physics
Identifiers
urn:nbn:se:kth:diva-171230 (URN)10.1007/978-3-319-30602-5_25 (DOI)000387431400025 ()2-s2.0-84978933952 (Scopus ID)978-331930600-1 (ISBN)
Conference
International Conference on Jets, Wakes and Separated Flows ( ICJWSF2015)
Note

QC 20150804. QC 20160226

Available from: 2015-07-24 Created: 2015-07-24 Last updated: 2017-01-10Bibliographically approved
Sundström, E., Semlitsch, B. & Mihaescu, M. (2016). Similarities and differences concerning flow characteristics in centrifugal compressors of different size. In: : . Paper presented at International Conference on Jets, Wakes and Separated Flows ( ICJWSF2015). Springer.
Open this publication in new window or tab >>Similarities and differences concerning flow characteristics in centrifugal compressors of different size
2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The appropriate choice of an automotive turbocharger compressor for an internal combustion engine is based on the compressor performance, which is commonly specified on a compressor map for different operating conditions. A wide operating range for the compressor covering all possible engine working conditions is desired. However, the application range of the compressor is limited. Different compressor designs are used to fit specific engine requirements. Naturally, these will have rather different characteristic compressor maps. The aim of the present investigation is to explain the differences in the compressor maps by analyzing the compressible flow-fields in two compressor designs from the same manufacturer, intended for a light-duty vehicle (passenger car). The flow-fields are assessed by steady-state Reynolds Averaged Navier-Stokes (RANS) simulations for several operating conditions. Similar flow features are observed near optimal efficiency operating conditions when the flow-field parameters are scaled properly. This study exposes the reason for the different measured operating ranges of the two compressors when ran at the same speed lines.

Place, publisher, year, edition, pages
Springer, 2016
Series
Springer Proceedings in Physics, ISSN 0930-8989 ; 185
Keyword
Centrifugal Compressor, Turbocharger, Fuel Efficiency
National Category
Fluid Mechanics and Acoustics
Research subject
Aerospace Engineering; Energy Technology
Identifiers
urn:nbn:se:kth:diva-171231 (URN)10.1007/978-3-319-30602-5_57 (DOI)000387431400057 ()2-s2.0-84979080235 (Scopus ID)978-331930600-1 (ISBN)
Conference
International Conference on Jets, Wakes and Separated Flows ( ICJWSF2015)
Funder
Swedish Energy Agency
Note

QC 20150805

Available from: 2015-07-24 Created: 2015-07-24 Last updated: 2016-12-22Bibliographically 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, 439-447 p.Conference 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
Keyword
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: 2016-12-22Bibliographically approved
Sundström, E., Semlitsch, B. & Mihaescu, M. (2015). Centrifugal Compressor: The Sound of Surge. In: 21st AIAA/CEAS Aeroacoustics Conference: . Paper presented at 21st AIAA/CEAS Aeroacoustics Conference, Meeting Location: Dallas, TX, 22-25 June 2015 (pp. 1-17). .
Open this publication in new window or tab >>Centrifugal Compressor: The Sound of Surge
2015 (English)In: 21st AIAA/CEAS Aeroacoustics Conference, 2015, 1-17 p.Conference paper, Published paper (Refereed)
Abstract [en]

When the centrifugal compressor operates at low mass flow rates (close to the unstable operating condition called surge), flow instabilities may develop and severe flow reversal may occur in the wheel passage. Under such conditions, noise generation has been reported resulting in a notable discomfort induced to the passengers in the cabin.

The aim with this study is to predict the flow field associated with a centrifugal compressor and characterize the acoustic near-field generation and propagation under stable and off-design (near-surge) operating conditions. The Large Eddy Simulation (LES) approach is employed. The unsteady features in the flow field leading to acoustic noise generation are quantified by means of statistical averaging, Fourier data analysis and flow mode decomposition techniques. The decomposition method is performed inside the rotating impeller region for several stable and off-design (including surge and near-surge) operating condi- tions. The acoustic near-field data are presented in terms of noise directivity maps and sound pressure level spectra.

For the near-surge condition an amplified broadband feature at two times the frequency of the rotating order of the shaft (possible whoosh noise) was captured. However, an amplified feature around 50% of the rotating order was captured as well. These features are present also during the investigated surge operating conditions, but occur at lower amplitudes as compared with the captured low surge frequency of 43 Hz. 

Keyword
Acoustic waves, Aeroacoustics, Centrifugal compressors, Centrifugation, Flow fields, Fourier series, Large eddy simulation, Decomposition methods, Flow instabilities, Low mass flow rates, Noise generation, Operating condition, Rotating impellers, Sound pressure level, Statistical Averaging, Acoustic noise
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
Identifiers
urn:nbn:se:kth:diva-169882 (URN)10.2514/6.2015-2674 (DOI)2-s2.0-84962514109 (Scopus ID)978-1-62410-367-4 (ISBN)
Conference
21st AIAA/CEAS Aeroacoustics Conference, Meeting Location: Dallas, TX, 22-25 June 2015
Note

QC 20160616

Available from: 2015-06-24 Created: 2015-06-24 Last updated: 2017-11-17Bibliographically approved
de Luzan, C. F., Chen, J., Mihaescu, M., Khosla, S. M. & Gutmark, E. (2015). Computational study of false vocal folds effects on unsteady airflows through static models of the human larynx. Journal of Biomechanics, 48(7), 1248-1257.
Open this publication in new window or tab >>Computational study of false vocal folds effects on unsteady airflows through static models of the human larynx
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2015 (English)In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 48, no 7, 1248-1257 p.Article in journal (Refereed) Published
Abstract [en]

Compressible large eddy simulation is employed to numerically investigate the laryngeal flow. Symmetric static models of the human larynx with a divergent glottis are considered, with the presence of false vocal folds (FVFs). The compressible study agrees well with that of the incompressible study. Due to the high enough Reynolds number, the flow is unsteady and develops asymmetric states downstream of the glottis. The glottal jet curvature decreases with the presence of FVFs or the ventricular folds. The gap between the FVFs stretches the flow structure and reduces the jet curvature. The presence of FVFs has a significant effect on the laryngeal flow resistance. The intra-glottal vortex structures are formed on the divergent wall of the glottis, immediately downstream of the separation point. The vortices are then convected downstream and characterized by a significant negative static pressure. The FVFs are a main factor in the generation of stronger vortices, and thus on the closure of the TVFs. The direct link between the FVFs geometry and the motion of the TVFs, and by extension to the voice production, is of interest for medical applications as well as future research works. The presence of the FVFs also changes the dominant frequencies in the velocity and pressure spectra.

Keyword
LES, Larynx, Vocal folds
National Category
Biophysics
Identifiers
urn:nbn:se:kth:diva-169352 (URN)10.1016/j.jbiomech.2015.03.010 (DOI)000353751200003 ()2-s2.0-84925816250 (Scopus ID)
Note

QC 20150612

Available from: 2015-06-12 Created: 2015-06-12 Last updated: 2017-12-04Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-7330-6965

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