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Large Eddy Simulations of Complex Flows in IC-Engine's Exhaust Manifold and Turbine
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.ORCID iD: 0000-0002-6603-0099
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The thesis deals with the flow in pipe bends and radial turbines geometries that are commonly found in an Internal Combustion Engine (ICE). The development phase of internal combustion engines relies more and more on simulations as an important complement to experiments. This is partly because of the reduction in development cost and the shortening of the development time. This is one of the reasons for the need of more accurate and predictive simulations. By using more complex computational methods the accuracy and predictive capabilities are increased. The disadvantage of using more sophisticated tools is that the computational time is increasing, making such tools less attractive for standard design purposes. Hence, one of the goals of the work has been to contribute to assess and improve the predictive capability of the simpler methods used by the industry.

By comparing results from experiments, Reynolds Averaged Navier-Stokes (RANS) computations, and Large Eddy Simulations (LES) the accuracy of the different computational methods can be established. The advantages of using LES over RANS for the flows under consideration stems from the unsteadiness of the flow in the engine manifold. When such unsteadiness overlaps the natural turbulence the model lacks a rational foundation. The thesis considers the effect of the cyclic flow on the chosen numerical models. The LES calculations have proven to be able to predict the mean field and the fluctuations very well when compared to the experimental data. Also the effects of pulsatile exhaust flow on the performance of the turbine of a turbocharging system is assessed. Both steady and pulsating inlet conditions are considered for the turbine case, where the latter is a more realistic representation of the real flow situation inside the exhaust manifold and turbine. The results have been analysed using different methods: single point Fast Fourier Transforms (FFT), probe line means and statistics, area and volume based Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD).

Abstract [sv]

Denna avhandling behandlar flödet i rörkrökar och radiella turbiner som vanligtvis återfinns i en förbränningsmotor. Utvecklingsfasen av förbränningsmotorer bygger mer och mer på att simuleringar är ett viktigt komplement till experiment. Detta beror delvis på minskade utvecklingskostnader men även på kortare utevklningstider. Detta är en av anledningarna till att man behöver mer exakta och prediktiva simuleringsmetoder. Genom att använda mer komplexa beräkningsmetoder så kan både nogrannheten och prediktiviteten öka. Nackdelen med att använda mer sofistikerade metoder är att beräkningstiden ökar, vilket medför att sådana verktyg är mindre attraktiva för standardiserade design ändamål. Härav, ett av målen med projektet har varit att bidra med att bedöma och förbättra de enklare metodernas prediktionsförmåga som används utav industrin.

Genom att jämföra resultat från experiment, Reynolds Averaged Navier-Stokes (RANS) och Large Eddy Simulations (LES) så kan nogrannheten hos de olika simuleringsmetoderna fastställas. Fördelarna med att använda LES istället för RANS när det gäller de undersökta flödena kommer ifrån det instationära flödet i grenröret. När denna instationäritet överlappar den naturligt förekommande turbulensen så saknar modellen en rationell grund. Denna avhandling behandlar effekten av de cykliska flöderna på de valda numeriska modellerna. LES beräkningarna har bevisats kunna förutsäga medelfältet och fluktuationerna väldigt väl när man jämför med experimentell data. Effekterna som den pulserande avgasströmning har på turboladdarens turbin prestanda har också kunnat fastställas. Både konstant och pulserande inlopps randvillkor har används för turbinfallet, där det senare är ett mer realistiskt representation av den riktiga strömningsbilden innuti avgasgrenröret och turbinen. Resultaten har analyserats på flera olika sätt: snabba Fourier transformer (FFT) i enskilda punkter, medelvärden och statistik på problinjer, area och volumsbaserade metoder så som Proper Orthogonal Decomposition (POD) samt Dynamic Mode Decomposition (DMD).

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , viii, 68 p.
Series
TRITA-MEK, ISSN 0348-467X ; 2014:20
Keyword [en]
Large Eddy Simulations, Reynolds Averaged Navier-Stokes, Turbocharger, Turbine, Curved Pipes, Pulsatile Flow, Proper Orthogonal Decomposition
Keyword [sv]
Large Eddy Simulations, Reynolds Averaged Navier-Stokes, Turboladdare, Turbin, Rörkrök, Pulserande Flöde, Proper Orthogonal Decomposition
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-151399ISBN: 978-91-7595-270-1 OAI: oai:DiVA.org:kth-151399DiVA: diva2:748463
Public defence
2014-10-03, D1, Lindstedtsvägen 17, 5tr, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20140919

Available from: 2014-09-19 Created: 2014-09-19 Last updated: 2014-09-19Bibliographically approved
List of papers
1. GT-Power Report
Open this publication in new window or tab >>GT-Power Report
2013 (English)Report (Other academic)
Abstract [en]

Presently in the vehicle industry full engine system simulations are performedusing dierent one-dimensional software programs in order to assess the eectof dierent geometrical and part changes on the system as a whole. Thesesimulations are usually fast and multiple parameters can be monitored andanalysed.In this report GT-Power simulations have been performed on a completeengine designed by Volvo Car Corporation. The investigation was performedin order to gain basic knowledge about the internal combustion engine andspecically about the gas exchange system and the turbocharger. A parameterstudy was performed and the responses on the turbine eciency and breaktorque were analysed.The trends in the simulation results follow the background theory well, i.e.increasing the turbine eciency increases the engine eciency and reduces thetime to torque. The eect of the valve opening times and durations on thebreak torque and the turbine eciency can be studied. There is an intricaterelationship where the optimal conguration is dependent on the engine speedas well as the opening angles and times.GT-Power is a very powerful tool for simulating complete engines. Howevercare must be taken when analysing the results. The code only uses one directionand time, meaning that the ow will always be uniform in the cross sections.Whereas in many parts of the real engine the ow eld is three dimensional andfar from uniform in the cross-sections.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-123083 (URN)
Note

QC 20130603

Available from: 2013-05-31 Created: 2013-05-31 Last updated: 2014-09-19Bibliographically approved
2. On the Importance of Turbulence Modelling of the Flow after a 90 Pipe Bend
Open this publication in new window or tab >>On the Importance of Turbulence Modelling of the Flow after a 90 Pipe Bend
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The flow in a free jet after a 90 pipe bend has been investigated by Large Eddy Simulations (LES) and Reynolds Averaged Navier-Stokes (RANS) simulations. The numerical results for the mean velocity profiles, flow fields, and power spectral densities have been compared to experimental data. The results show that LES has been able to predict the mean components of the velocity field and in resolving dynamic motions such as vortex switching. LES without an explicit SGS model (termed as ILES in the following) has been found to work well with flows of this type as long as the grid resolution is sufficiently fine. Different Sub-Grid-Scale (SGS) models have also been used. LES with different SGS models result in very similar results when a fine enough grid is used. The ILES approach also gives reasonably accurate results for the mean values even for coarser grids.

National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-151395 (URN)
Note

QS 2014

Available from: 2014-09-19 Created: 2014-09-19 Last updated: 2014-09-19Bibliographically approved
3. Analysis of Secondary Flow Induced by a 90 Bend in a Pipe Using Mode Decomposition Techniques
Open this publication in new window or tab >>Analysis of Secondary Flow Induced by a 90 Bend in a Pipe Using Mode Decomposition Techniques
2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

In this study unsteady simulations of the flow through and after a 90 pipe bend has been performed by Large Eddy Simulations (LES). In the passenger car engine there is an abundance of pipes and pipe bends. Since pipes and bends are often situated upstream of important engine components the flow in these needs to be well predicted. This entails that there is a need for accurate pipe flow simulations in order to ensure that the inflow conditions, to the e.g. cylinders or turbocharger, are as close to the experimental values as possible. The flow field is further studied by the use of Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD). It has been found that there is a low frequency oscillation in the strength of the alternately dominant dean vortex at the exit of the pipe bend. This phenomenon is analysed and the mechanism for it is discussed.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-151397 (URN)
Conference
4th International Conference on Jets, Wakes and Separated Flows, ICJWSF2013
Note

QC 20140919

Available from: 2014-09-19 Created: 2014-09-19 Last updated: 2014-09-19Bibliographically approved
4. Effects of Pulsation Frequency and Pulse Shape on Turbine Performance
Open this publication in new window or tab >>Effects of Pulsation Frequency and Pulse Shape on Turbine Performance
(English)Manuscript (preprint) (Other academic)
Abstract [en]

  The current paper studies the pulsating flow in the exhaust manifold and turbine of a passenger car engine. The study focuses on three engine RPMs and two different pulse shapes, one normal shape and one shorter DEP like shape. By simulating different valve strategies one can investigate how to maximize the available exhaust flow energy to the turbine. The simulations have been performed with the Large Eddy Simulation (LES) method with boundary conditions received from GT-Power simulations. The study focuses on kinetic energy and turbine torque analysis of the incoming flow and of the flow in the turbine wheel region. It is found that the pulse shape is affecting the wheel torque significantly and that the kinetic energy entering the wheel region is different depending on which cylinder fired.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-151398 (URN)
Note

QS 2014

Available from: 2014-09-19 Created: 2014-09-19 Last updated: 2014-09-19Bibliographically approved
5. Analysis of 3 Dimensional Turbine Flow by using Mode Decomposition Techniques
Open this publication in new window or tab >>Analysis of 3 Dimensional Turbine Flow by using Mode Decomposition Techniques
2014 (English)In: Proceedings of the ASME Turbo Expo, 2014, GT2014-26963- p.Conference paper, Published paper (Refereed)
Abstract [en]

 Today one of the most popular ways of lowering the fuel consumption and emissions of the Internal Combustion Engine (ICE) is by downsizing the engine. Downsizing means that the swept volumes of the cylinders are decreased; this lowers the frictional and thermal losses. By combining the downsizing with a well matched turbocharger system the performance is preserved while the advantages are retained. Since more and more of the development work is being performed by simulations there is an increasing need for more accurate methods. These methods are more complex and require more resources than the simpler, faster and more robust models used today. In this study Large Eddy Simulations (LES) of the unsteady flow in a radial turbine designed for a gasoline ICE has been performed and analysed. The flow inside the turbine is highly 3 dimensional, pulsating and characterized by secondary flow motions and high curvatures. All these are reasons for which the method of choice should be LES. LES is able to resolve a large range of scales and capture the flow dynamics. The considered case concerns a non-pulsating flow condition but with engine like mass flow and temperature. Post-processing tools based on Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) are used to analyse the large amount of LES based flow data. The POD method is used to investigate the energy content of the dominant, large structures present in the flow. The DMD method on the other hand is used to reveal the flow structures responsible for specific frequencies found in the flow field. Preliminary data show a fair agreement between experimental data and LES results in terms of predicting the turbine performance parameters.

National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-151390 (URN)10.1115/GT2014-26963 (DOI)000361923800084 ()2-s2.0-84922265228 (Scopus ID)9780791845639 (ISBN)
Conference
ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, GT 2014; Dusseldorf; Germany; 16 June 2014 through 20 June 2014
Note

QC 20140919

Available from: 2014-09-19 Created: 2014-09-19 Last updated: 2015-10-29Bibliographically approved
6. Effects of inlet geometry on turbine performance
Open this publication in new window or tab >>Effects of inlet geometry on turbine performance
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In this study comparisons have been performed between gas-stand experiments,Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations, and LargeEddy Simulations (LES) of the ow through a radial turbine of a turbochargerdesigned for an internal combustion engine. The long term goal for the projectis to improve the prediction capabilities for the simpler computational modelsused by industry in the research and development of new products. At thepresent stage the eects of using simplied geometries and methods for turbineperformance predictions are assessed. Additionally, data obtained from URANScalculations is compared against experimental data and against unsteady LESresults. The comparisons are made in order to evaluate the employed methodologies,to know when to use simplied models with reasonable accuracy, as wellas to justify the use of more advanced methods when the models are inadequate.It was found out that the LES results are closer to the gas-stand experimentsthan the URANS predictions are.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-123084 (URN)
Note

QS 2013

Available from: 2013-05-31 Created: 2013-05-31 Last updated: 2014-09-19Bibliographically approved

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