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Publications (10 of 92) Show all publications
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)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: 2018-10-16Bibliographically 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
Ceci, A., Gojon, R. & Mihaescu, M. (2018). Large Eddy Simulations for Indirect Combustion Noise Assessment in a Nozzle Guide Vane Passage. Flow Turbulence and Combustion, 1-13
Open this publication in new window or tab >>Large Eddy Simulations for Indirect Combustion Noise Assessment in a Nozzle Guide Vane Passage
2018 (English)In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Flow, Turbulence and Combustion, ISSN 1386-6184, p. 1-13Article in journal (Refereed) Published
Abstract [en]

The combustion noise in aero-engines is known to originate from two different sources. First, the unsteady heat release in the combustion chamber generates the direct combustion noise. Second, hot and cold spots of air generated by the combustion process are convected and accelerated by the turbine stages and give rise to the so-called indirect combustion noise. The present work targets, by using a numerical approach, the generation mechanism of indirect combustion noise for a simplified geometry of a turbine stator passage. Periodic temperature fluctuations are imposed at the inlet, permitting to simulate hot and cold packets of air coming from the unsteady combustion. Three-dimensional Large Eddy Simulation (LES) calculations are conducted for transonic operating conditions to evaluate the blade acoustic response to the forced temperature perturbations at the inlet plane. Transonic conditions are characterized by trailing edge expansion waves and shocks. It is notably shown that their movement can be excited if disturbances with a particular frequency are injected in the domain.

Place, publisher, year, edition, pages
Springer, 2018
Keywords
Large Eddy Simulation, Aeroacoustics, Indirect combustion noise, Entropy noise
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-235797 (URN)10.1007/s10494-018-9964-9 (DOI)2-s2.0-85052594186 (Scopus ID)
Note

QC 20181008

Available from: 2018-10-04 Created: 2018-10-04 Last updated: 2018-10-08Bibliographically approved
Gojon, R., Bogey, C. & Mihaescu, M. (2018). Oscillation Modes in Screeching Jets. AIAA Journal, 56(7), 2918-2924
Open this publication in new window or tab >>Oscillation Modes in Screeching Jets
2018 (English)In: AIAA Journal, ISSN 0001-1452, E-ISSN 1533-385X, Vol. 56, no 7, p. 2918-2924Article in journal (Refereed) Published
Abstract [en]

Nonideally expanded supersonic jets generate three basic noise components, namely, the turbulent mixing noise, the broadband shock-associated noise, and the screech noise. The mixing noise, obtained for both subsonic and supersonic jets, is most intense in the downstream direction; and it occurs at Strouhal numbers of around 0.15. The broadband shock-associated noise is radiated mainly in the radial direction, and it has a central frequency varying with the emission angle. The screech noise consists of tones measured in the upstream direction. These tones are due to an aeroacoustic feedback mechanism establishing between turbulent structures propagating downstream and acoustic waves propagating upstream.

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics, 2018
Keywords
Supersonic jets; screech noise; origin of the oscillation modes; vortex sheet model; Large Eddy Simulations
National Category
Aerospace Engineering Fluid Mechanics and Acoustics
Research subject
Aerospace Engineering; Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-228596 (URN)10.2514/1.J056936 (DOI)000436234200035 ()2-s2.0-85049147886 (Scopus ID)
Note

QC 20180717

Available from: 2018-05-28 Created: 2018-05-28 Last updated: 2018-07-17Bibliographically approved
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
Keywords
Radial compressor, 1D model, RANS, performance prediction
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-206518 (URN)2-s2.0-85043425635 (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: 2018-05-16Bibliographically 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.

Keywords
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
Keywords
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.

Keywords
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
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-7330-6965

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