scholarly journals Development and validation of a hybrid temporal LES model in the perspective of applications to internal combustion engines

2019 ◽  
Vol 74 ◽  
pp. 56
Author(s):  
Al Hassan Afailal ◽  
Jérémy Galpin ◽  
Anthony Velghe ◽  
Rémi Manceau
Keyword(s):  
Steady Flow ◽  
Channel Flow ◽  
Internal Combustion Engines ◽  
Internal Combustion ◽  
Core Region ◽  
Wall Region ◽  
Combustion Engines ◽  
The Core ◽  
Les Model ◽  
Near Wall

CFD simulation tools are increasingly used nowadays to design more fuel-efficient and clean Internal Combustion Engines (ICE). Within this framework, there is a need to benefit from a turbulence model which offers the best compromise between prediction capabilities and computational cost. The Hybrid Temporal LES (HTLES) approach is here retained within the perspective of an application to ICE configurations. HTLES is a hybrid Reynolds-Averaged Navier Stokes/Large Eddy Simulation (RANS/LES) model based on a solid theoretical framework using temporal filtering. The concept is to model the near-wall region in RANS and to solve the turbulent structures in the core region if the temporal and spatial resolutions are fine enough. In this study, a dedicated sub-model called Elliptic Shielding (ES) is added to HTLES in order to ensure RANS in the near-wall region, regardless of the mesh resolution. A modification of the computation of the total kinetic energy and the dissipation rate was introduced as first adaptions of HTLES towards non-stationary ICE configurations. HTLES is a recent approach, which has not been validated in a wide range of applications. The present study intends to further validate HTLES implemented in CONVERGE code by examining three stationary test cases. The first validation consists of the periodic hill case, which is a standard benchmark case to assess hybrid turbulence models. Then, in order to come closer to real ICE simulations, i.e., with larger Reynolds numbers and coarser near-wall resolutions, the method is validated in the case of a channel flow using wall functions and in the steady flow rig case consisting in an open valve at a fixed lift. HTLES results are compared to RANS k-ω SST and wall-modeled LES σ simulations performed with the same grid and the same temporal resolution. Unlike RANS, satisfactory reproduction of the flow recirculation has been observed with HTLES in the case of periodic hills. The channel flow configuration has underlined the capability of HTLES to predict the wall friction properly. The steady flow rig shows that HTLES combines advantages of RANS and LES in one simulation. On the one hand, HTLES yields mean and rms velocities as accurate as LES since the scale-resolving simulation is triggered in the core region. On the other hand, hybrid RANS/LES at the wall provides accurate pressure drop in contrast with LES performed on the same mesh. Future work will be dedicated to the extension of HTLES to non-stationary flows with moving walls in order to be able to tackle realistic ICE flow configurations.

Turbulent drag reduction in plane Couette flow with polymer additives: a direct numerical simulation study

2018 ◽  
Vol 846 ◽  
pp. 482-507 ◽  
Author(s):  
Hao Teng ◽  
Nansheng Liu ◽  
Xiyun Lu ◽  
Bamin Khomami
Keyword(s):  
Numerical Simulation ◽  
Drag Reduction ◽  
Large Scale ◽  
Core Region ◽  
Wall Region ◽  
Plane Couette Flow ◽  
The Core ◽  
Elastic Potential Energy ◽  
Conformation Tensor ◽  
Near Wall

Drag reduction (DR) in plane Couette flow (PCF) induced by the addition of flexible polymers has been studied via direct numerical simulation (DNS). The similarities and differences in the drag reduction features of PCF and plane Poiseuille flow (PPF) have been examined in detail, particularly in regard to the polymer-induced modification of large-scale structures (LSSs) in the near-wall turbulence. Specifically, it has been demonstrated that in the near-wall region, drag-reduced PCF has features similar to those of drag-reduced PPF; however, in the core region, intriguing differences are found between these two drag-reduced shear flows. Chief among these differences is the significant polymer stretch that arises from the enhanced exchanges between elastic potential energy and turbulent kinetic energy and the commensurate observation of peak values of the conformation tensor components $\unicode[STIX]{x1D60A}_{yy}$ and $\unicode[STIX]{x1D60A}_{zz}$ in this region. This finding is in stark contrast to that of drag-reduced PPF where the polymer stretch and the exchanges between elastic potential energy and turbulent kinetic energy in the core region are insignificant; to this end, in drag-reduced PPF, peak values of the conformation tensor components appear in the near-wall region. Therefore, this study paves the way for understanding the underlying flow physics in drag-reduced PCF, particularly in the context of elastic theory. Moreover, the longitudinal large-scale streaks at the channel centre of drag-reduced PCF are greatly strengthened due to the increased production/dissipation ratio; the LSS imprint effects on the near-wall flow of drag-reduced PCF monotonically increase as the Weissenberg number is enhanced.

scholarly journals The application of carbon nanotubes for reducing the friction losses of internal combustion engine

2015 ◽  
Vol 162 (3) ◽  
pp. 64-77
Author(s):  
Jarosław KAŁUŻNY ◽  
Antoni ISKRA ◽  
Michael GIERSIG ◽  
Krzysztof KEMPA
Keyword(s):  
Carbon Nanotubes ◽  
Industrial Application ◽  
Internal Combustion Engines ◽  
Main Part ◽  
Combustion Engine ◽  
Internal Combustion ◽  
Original Study ◽  
Combustion Engines ◽  
The Core ◽  
Intensive Investigation

Carbon nanotubes are a relatively new allotropic variety of carbon and due to a number of very favorable properties – including chemical and mechanical – are now under intensive investigation. Introduction to the main part of the article requires an overview of carbon nanotubes studies conducted by different authors, the results of which can provide important guidelines for possible use of the material in the construction of piston engines. The core of the article is the description of attempts to use carbon nanotubes made by the authors in order to improve the functional properties of various components of internal combustion engines, in particular to reduce losses caused by friction. Therefore, the results from the original study have been presented which indicate that the use of carbon nanotubes as an additive for engine lubricant can contribute to a significant reduction in friction losses. Article concludes with a discussion of the tasks that need to be completed in order to allow for an industrial application of carbon nanotubes.

Effects of an axisymmetric contraction on a turbulent pipe flow

2011 ◽  
Vol 687 ◽  
pp. 376-403 ◽  
Author(s):  
Seong Jae Jang ◽  
Hyung Jin Sung ◽  
Per-Åge Krogstad
Keyword(s):  
Pipe Flow ◽  
Core Region ◽  
Turbulent Pipe Flow ◽  
Wall Region ◽  
Mean Flow ◽  
The Core ◽  
Thin Region ◽  
Local Mean ◽  
The Mean ◽  
Near Wall

AbstractThe flow in an axisymmetric contraction fitted to a fully developed pipe flow is experimentally and numerically studied. The reduction in turbulence intensity in the core region of the flow is discussed on the basis of the budgets for the various turbulent stresses as they develop downstream. The contraction generates a corresponding increase in energy in the near-wall region, where the sources for energy production are quite different and of opposite sign compared to the core region, where these effects are caused primarily by vortex stretching. The vortices in the pipe become aligned with the flow as the stretching develops through the contraction. Vortices which originally have a spanwise component in the pipe are stretched into pairs of counter-rotating vortices which become disconnected and aligned with the mean flow. The structures originating in the pipe which are inclined at an angle with respect to the wall are rotated towards the local mean streamlines. In the very near-wall region and the central part of the contraction the flow tends towards two-component turbulence, but these structures are different. The streamwise and azimuthal stresses are dominant in the near-wall region, while the lateral components dominate in the central part of the flow. The two regions are separated by a rather thin region where the flow is almost isotropic.

Paper 3: Non-Steady Flow in Internal Combustion Engine Inlet and Exhaust Systems

1969 ◽  
Vol 184 (7) ◽  
pp. 7-16 ◽  
Author(s):  
R. S. Benson ◽  
J. S. Foxcroft
Keyword(s):  
Standard Deviation ◽  
Steady Flow ◽  
Internal Combustion Engines ◽  
Method Of Characteristics ◽  
Internal Combustion ◽  
Combustion Engines ◽  
Steady Flows ◽  
The Method Of Characteristics ◽  
Mass Flows ◽  
Exhaust Systems

Previous work on non-steady flow in exhaust systems has shown that the method of characteristics can be used to predict the flow conditions to a high degree of accuracy. In these calculations the pressure at the inlet port or valve was considered to be constant. Recent work on the effect of pulsating flow on centrifugal compressors has shown the importance of considering non-steady flows in the inlet systems of supercharged engines. Predictions of the non-steady flow in inlet systems, usually based on acoustic theory, have only been accurate in particular cases. In this paper the method of characteristics has been applied to the study of non-steady flows both in the inlet and exhaust systems of internal combustion engines. Comparisons are made between the calculated and experimental results obtained on a multi-cylinder pulse generator. Tests on both single- and two-cylinder units were carried out and measurements of the inlet pipe pressure, exhaust pipe pressure, cylinder pressures and temperatures, and inlet and exhaust mass flows were made. Comparisons between the theoretical predictions and the test results were extremely good; in all the cases the pressures were in close agreement. The inlet predicted mass flows were all within +9 and −4 per cent of the measured flows, the standard deviation being 3·1 per cent. The exhaust mass flows were all within +8 and −12 per cent of the measured mass flows, the standard deviation being 4·3 per cent. It was considered that the method gives reliable predictions of the flow processes in internal combustion engines.

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