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Assessment of Heat Transfer Effects on the Performance of a Radial Turbine using Large Eddy Simulation
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. SAAB Automobile Powertrain, Sweden .
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
2010 (English)In: 9th International Conference on Turbochargers and Turbocharging - Institution of Mechanical Engineers, Combustion Engines and Fuels Group, 2010, 281-291 p.Conference paper (Refereed)
Abstract [en]

One way to reduce fuel consumption and emissions is to downsize the engine in combination with turbo-charging. The turbine works under highly unsteady flow conditions, since the exhaust flow is pulsatile, turbulent and with a varying strength of the axial and secondary flow components. The heat transfer from the fluid to the turbine housing will be different for a pulsatile flow compared to a non-pulsatile flow. Therefore, the effects of heat transfer at the walls on the turbine performance working under pulsatile flow conditions are assessed and quantified by performing a numerical study with Large Eddy Simulation. Two cases are considered, one case with adiabatic walls and one case with heat transfer at the walls. The results show that the difference in the obtained shaft power is small. Even the differences in the time mean efficiency is small, it only differs with 2 percent units, even though the heat transferred to surroundings is as large as approximately 60 percent of the delivered shaft power.

Place, publisher, year, edition, pages
2010. 281-291 p.
Keyword [en]
Adiabatic wall, Exhaust flow, Flow condition, Heat transfer effects, Numerical studies, Radial turbines, Shaft power, Turbine housings, Turbine performance
National Category
Energy Engineering
URN: urn:nbn:se:kth:diva-12739DOI: 10.1243/17547164C0012010022ScopusID: 2-s2.0-79959600664ISBN: 978-190759915-6OAI: diva2:318478
9th International Conference on Turbochargers and Turbocharging; Westminster, London; United Kingdom; 19 May 2010 through 20 May 2010


Available from: 2010-05-07 Created: 2010-05-07 Last updated: 2014-09-03Bibliographically 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.
Trita-MEK, ISSN 0348-467X ; 2010:03
Turbochargers, turbine, compressor, unsteady pulsatile flow, perturbations, Large Eddy Simulation
National Category
Fluid Mechanics and Acoustics
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)
QC20100622Available from: 2010-05-10 Created: 2010-05-07 Last updated: 2010-11-11Bibliographically approved

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