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Analysis of shortcomings with 1-D engine calculations by means of 3-D computations on components
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , 126 p.
Series
Trita-MMK, ISSN 1400-1179 ; 2010:02
Identifiers
URN: urn:nbn:se:kth:diva-13095ISBN: 978-91-7415-613-3 (print)OAI: oai:DiVA.org:kth-13095DiVA: diva2:320824
Public defence
2010-05-26, Sal M3, Brinellvägen 64, KTH, Stockholm, 11:30 (English)
Opponent
Supervisors
Note
QC 20100922Available from: 2010-05-27 Created: 2010-05-27 Last updated: 2010-09-22Bibliographically approved
List of papers
1. Instantaneous On-Engine Turbine Efficiency for an SI Engine in the Closed Waste Gate Region for 2 Different Turbochargers
Open this publication in new window or tab >>Instantaneous On-Engine Turbine Efficiency for an SI Engine in the Closed Waste Gate Region for 2 Different Turbochargers
2006 (English)In: SAE Technical Papers, 2006, no 01-3389Conference paper, Published paper (Refereed)
Abstract [en]

1D engine simulations of turbocharged engines are difficult to perform with good accuracy. Calculations of turbine performance are based on performance maps. These are measured under steady flow conditions using air at moderate temperatures, not very representative of the very hot and pulsating gas flow the on-engine turbine is exposed to. To improve the predictivity of today's 1D engine calculations or the limiting factors of the turbocharger itself, it is most important to gain deeper understanding of how the turbine behaves under on-engine conditions.

The objective of this paper is to compare calculated instantaneous on-engine turbine efficiency based on measurements with results from using steady-flow efficiency performance maps. The work is performed using two different turbochargers at two operating points with closed waste gate.

It is shown that the turbine efficiency characteristic derived from measurements and that from using steady-flow efficiency performance maps describe a quite different behavior of the turbine. The on-engine turbine efficiency has systematically shown to be asymmetric over an exhaust pulse. It is considerably higher during the “downhill side” of the pulse, a phenomenon not captured by the 1D quasi steady calculations.

An error estimation is made for the measurement-based efficiency. The cumulative error results from individual measurement errors of its constituent parameters. The efficiency uncertainty is most governed and very sensitive to the measurement error of the turbine shaft speed. The pressure before and after the turbine are also important to measure correctly.

Identifiers
urn:nbn:se:kth:diva-24679 (URN)10.4271/2006-01-3389 (DOI)2-s2.0-79959848121 (Scopus ID)
Note

QC 20100922

Available from: 2010-09-22 Created: 2010-09-22 Last updated: 2017-04-28Bibliographically approved
2. A Comparative Study Between 1D and 3D Computational Results for Turbulent Flow in an Exhaust Manifold and in Bent Pipes
Open this publication in new window or tab >>A Comparative Study Between 1D and 3D Computational Results for Turbulent Flow in an Exhaust Manifold and in Bent Pipes
2009 (English)In: SAE Technical Papers, 2009, no 01-1112Conference paper, Published paper (Refereed)
Abstract [en]

To improve today’s 1D engine simulation techniques it is important to investigate how well complex geometries such as the manifold are modeled by these engine simulation tools and to identify the inaccuracies that can be attributed to the 1D assumption. Time resolved 1D and 3D calculations have been performed on the turbulent flow through the outer runners of an exhaust manifold of a 2 liter turbocharged SI engine passenger car

The total pressure drop over the exhaust manifold, computed with the 1D and 3D approach, showed to differ over an exhaust pulse. This is so even though a pressure loss coefficient correction has been employed in the 1D model to account for 3D flow effects.

The 3D flow in the two outer runners of the manifold shows the presence of secondary flow motion downstream of the first major curvature. The axial velocity profile downstream of the first turn loses its symmetry. As the flow enters the second curvature a swirling motion is formed. This secondary flow motion prevails with considerable strength at the outlet plane, where the two runners join.

The turbulent flow through single bent pipes with different turning angle as well as a double bent pipe is also computed using both the 1D and the 3D model, the double bent pipe also for time-varying flow. The results are expressed and compared in terms of pressure losses.

The results show that a comparison between 1D and 3D computed pressure loss through a bent geometry is only reasonable for cases where the downstream portion of the pipe after the bend is long enough. This does not hold for geometries like an engine exhaust manifold.

Identifiers
urn:nbn:se:kth:diva-24681 (URN)10.4271/2009-01-1112 (DOI)2-s2.0-84877239733 (Scopus ID)
Note

QC 20100922

Available from: 2010-09-22 Created: 2010-09-22 Last updated: 2017-04-28Bibliographically approved
3. Study of Junctions in 1-D & 3-D Simulation for Steady and Unsteady Flow
Open this publication in new window or tab >>Study of Junctions in 1-D & 3-D Simulation for Steady and Unsteady Flow
2010 (English)In: SAE technical paper series, ISSN 0148-7191, no 01-1050Article in journal (Refereed) Published
Abstract [en]

In this work a comparative study between 1-D and 3-D calculations has been performed on different junctions. The geometries are a 90° T-junction with an area ratio of unity and a 45° junction with an area ratio of 1.78 between the main pipe and the side branch. The latter case had an offset between the centerlines of the main and the branched pipe. The 3-D modeling framework uses the Reynolds Averaged Navier-Stokes (RANS) equations with the k-ε model both for the steady and the unsteady flow cases. The comparison is made both under steady and pulsating flow conditions. The aim has been to assess the 1-D/3-D differences in terms of measures for flow losses.

There are large discrepancies between the 1-D and 3-D computed losses in junctions. The relative differences between 1-D and 3-D computed losses in isentropic power are 63 % and 175 % for the 90° and the 45 ° junctions without including the losses in downstream pipe legs. These figures are reduced to 12 % and 114 % respectively when including a straight pipe segment of one diameter downstream of the junction outlets.

For the 90° junction at pulsating flow, the discrepancy in 1-D and 3-D computed loss is lower compared to the steady flow case if comparing only the losses in the junction, but similar to the steady discrepancy if including the downstream pipe losses. For the 45° junction, the discrepancies are much larger. The 1-D loss is near six times that of the corresponding 3-D value if comparing the losses in the junction alone, and 3 times the 3-D value if including the losses in 10 diameter of the outlet pipe.

Place, publisher, year, edition, pages
Society of Automotive Engineers, 2010
Keyword
3-d modeling, 3D simulations, Area ratios, Branched pipes, Centerlines, Comparative studies, Flow loss, Isentropic, Pulsating flow, Reynolds-Averaged Navier-Stokes equations, Side branches, Straight pipe, T junctions
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-24682 (URN)10.4271/2010-01-1050 (DOI)2-s2.0-84877210948 (Scopus ID)
Note

QC 20100922

Available from: 2010-09-22 Created: 2010-09-22 Last updated: 2017-12-12Bibliographically approved
4. Predictions of the Performance of a Radial Turbine with Different Modeling Approaches: Comparison of the Results from 1-D and 3-D CFD
Open this publication in new window or tab >>Predictions of the Performance of a Radial Turbine with Different Modeling Approaches: Comparison of the Results from 1-D and 3-D CFD
2010 (English)In: SAE technical paper series, ISSN 0148-7191, no 01-1223Article in journal (Refereed) Published
Abstract [en]

In this paper, the performance of a radial turbine working under pulsatile flow conditions is computed with two different modeling approaches, time resolved 1-dimensional (1-D) and 3-dimensional (3-D) CFD. The 1-D modeling approach is based on measured turbine maps which are used to compute the mass flow rate and work output from the turbine for a given expansion ratio and temperature at the inlet. The map is measured under non-pulsatile flow conditions, and in the 1-D method the turbine is treated as being a quasi-stationary flow device. In the 3-D CFD approach, a Large Eddy Simulation (LES) turbulence approach is used. The objective of LES is to explicitly compute the large scales of the turbulence while modeling the effects of the unresolved scales.

Three different cases are considered, where the simplest case only consist of the turbine and the most complex case consist of an exhaust manifold and the turbine. Both time resolved data, such as pressure ratio, temperature and shaft torque and time mean data from the two different modeling approaches are compared. The results show that the computed time mean shaft power differs between the two different modeling approaches with as much as 100%. Since the considered operation point for the engine in this study is 1500 rpm with wide open throttle, the turbine operates in an area where the turbine map is extrapolated. Only by using a few operation points from CFD to extend the map, an improvement is achieved for the 1-D results, but still the deviation is large. Also, the pressure ratio and temperature drop over the turbine differs for the used modeling approaches. The causes for the deviations are assessed and discussed to get a better understanding of eventually limitations of the 1-D modeling approach.

Identifiers
urn:nbn:se:kth:diva-24683 (URN)10.4271/2010-01-1223 (DOI)2-s2.0-84877226366 (Scopus ID)
Note

QC 20100922

Available from: 2010-09-22 Created: 2010-09-22 Last updated: 2017-04-18Bibliographically approved

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