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Large Eddy Simulation of the Unsteady Flow in a Radial Compressor Operating Near Surge
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
Department of Aerospace, Engineering and Engineering Mechanics, University of Cincinnati.
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
2012 (English)In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 134, no 5, 051006- p.Article in journal (Refereed) Published
Abstract [en]

The flow in a centrifugal compressor has been computed using large eddy simulation (LES). The investigated geometry is that of a ported shroud compressor with a 10 blade impeller with an exducer diameter of 88 mm. The computational data compares favorably with measured data for the same compressor and operational point. For the considered operational point near surge, the flow field in the entire compressor stage is unsteady. Back-flow occurs in the diffuser, wheel, and the ported shroud channels resulting in back-flow at the walls in the inlet region of the compressor. In the diffuser and volute, the flow is highly unsteady with perturbations that are convected around the volute, affecting the flow field in most of the entire compressor. The mechanism driving this unsteadiness is assessed by flow visualizations, frequency analysis, and correlations of pressure and velocity data in order to gain a more comprehensive understanding of the mechanism leading to stall and surge.

Place, publisher, year, edition, pages
2012. Vol. 134, no 5, 051006- p.
Keyword [en]
Blade impeller, Compressor stage, Computational data, Frequency Analysis, Measured data, Radial compressors
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-12741DOI: 10.1115/1.4003816ISI: 000308404500006Scopus ID: 2-s2.0-84860681469OAI: oai:DiVA.org:kth-12741DiVA: diva2:318484
Funder
Swedish e‐Science Research Center
Note

QC 20120621. Updated from manuscript to article in journal.

Available from: 2010-05-07 Created: 2010-05-07 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Numerical computations of the unsteady flow in turbochargers
Open this publication in new window or tab >>Numerical computations of the unsteady flow in turbochargers
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Turbocharging the internal combustion (IC) engine is a common technique to increase the power density. If turbocharging is used with the downsizing technique, the fuel consumption and pollution of green house gases can be decreased. In the turbocharger, the energy of the engine exhaust gas is extracted by expanding it through the turbine which drives the compressor by a shaft. If a turbocharged IC engine is compared with a natural aspirated engine, the turbocharged engine will be smaller, lighter and will also have a better efficiency, due to less pump losses, lower inertia of the system and less friction losses. To be able to further increase the efficiency of the IC engine, the understanding of the highly unsteady flow in turbochargers must be improved, which then can be used to increase the efficiency of the turbine and the compressor. The main objective with this thesis has been to enhance the understanding of the unsteady flow in turbocharger and to assess the sensitivity of inflow conditions on the turbocharger performance.

The performance and the flow field in a radial turbocharger turbine working under both non-pulsatile and pulsatile flow conditions has been assessed by using Large Eddy Simulation (LES). To assess the effects of different operation conditions on the turbine performance, different cases have been considered with different perturbations and unsteadiness of the inflow conditions. Also different rotational speeds of the turbine wheel were considered. The results show that the turbine cannot be treated as being quasi-stationary; for example,the shaft power varies for different frequencies of the pulses for the same amplitude of mass flow. The results also show that perturbations and unsteadiness that are created in the geometry upstream of the turbine have substantial effects on the performance of the turbocharger. All this can be summarized as that perturbations and unsteadiness in the inflow conditions to the turbine affect the performance.

The unsteady flow field in ported shroud compressor has also been assessed by using LES for two different operational points. For an operational point near surge, the flow field in the entire compressor stage is unsteady, where the driving mechanism is an unsteadiness created in the volute. For an operational point far away from surge, the flow field in the compressor is relatively much more steady as compared with the former case. Although the stable operational point exhibits back-flow from the ported shroud channels, which implies that the flow into the compressor wheel is disturbed due to the structures that are created in the shear layer between the bulk flow and the back-flow from the ported shroud channels.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. vi, 100 p.
Series
Trita-MEK, ISSN 0348-467X ; 2010:03
Keyword
Turbochargers, turbine, compressor, unsteady pulsatile flow, perturbations, Large Eddy Simulation
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-12742 (URN)978-91-7415-632-4 (ISBN)
Public defence
2010-05-26, F3, Lindsedsv, 26, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC20100622Available from: 2010-05-10 Created: 2010-05-07 Last updated: 2010-11-11Bibliographically approved

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