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Numerical computations of the pulsatile flow in a turbocharger with realistic inflow conditions from an exhaust manifold
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
2009 (English)In: ASME Turbo Expo 2009: Power for Land, Sea and Air, 2009Conference paper, Published paper (Refereed)
Abstract [en]

The combined effect of different secondary perturbations at the turbine inlet and the pulsatile flow on the turbine performance was assessed and quantified by using Large Eddy Simulation. The geometrical configuration consists of a 4-1 exhaust manifold and a radial turbine. At the inlet to each port of the manifold, engine realistic pulsatile mass flow and temperature fields are specified. The turbine used in this numerical study is a vaneless radial turbine with 9 blades, with a size that is typical for a turbocharger mounted on a 2.0 liters IC engine of passenger cars. The flow field is investigated and the generated vortices are visualized to enable a better insight into the unsteady flow field. Correlations between the turbine inflow conditions, such as massflow rate, strength of secondary flow components, and the turbine performance have also been studied. The results show that the flow field entering the turbine is heavily disturbed with strong secondary flow components and disturbed axial velocity profile. Between the inlet to the turbine and the wheel, the strength of the secondary flow and the level of the disturbances of the axial flow decrease which gives large losses in this region. Even though the magnitude of the disturbances decrease, the flow entering the wheel will still be disturbed, resulting in a perturb inlet flow to the wheel which affects the shaft power output from the turbine.

Place, publisher, year, edition, pages
2009.
Series
GT2009-59619
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-12737OAI: oai:DiVA.org:kth-12737DiVA: diva2:318473
Conference
ASME Turbo Expo 2009, Power for Land, Sea and Air
Note
QC 20100617Available from: 2010-05-07 Created: 2010-05-07 Last updated: 2010-06-22Bibliographically 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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