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Energies
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Large-Eddy Simulations of Turbulent Flows
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Large-Eddy Simulations of Turbulent Flows

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "J: Thermal Management".

Deadline for manuscript submissions: closed (20 December 2019) | Viewed by 8567

Special Issue Editors

Prof. Dr. Assensi Oliva

E-Mail Website
Guest Editor
Heat and Mass Transfer Technological Center, Technical University of Catalonia, ESEIAAT, Colom 11, 08222 Terrassa (Barcelona), Spain
Interests: heat and mass transfer; CFD; large-eddy simulation; HPC; multiphase flows; numerical methods
Prof. F. Xavier Trias

E-Mail Website
Guest Editor
Heat and Mass Transfer Technological Center, Technical University of Catalonia, ESEIAAT, Colom 11, Terrassa, 08222 Barcelona, Spain
Interests: fluid mechanics; turbulence modeling; CFD; large-eddy simulation; direct numerical simulation; applied mathematics and numerical methods
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Special Issue Information

Dear colleagues,

The Navier-Stokes (NS) equations are an excellent mathematical model for turbulent flows. However, direct simulations at high Reynolds numbers are not feasible yet because the non-linear convective term produces far too many scales of motion. Hence, in the foreseeable future, numerical simulations of turbulent flows will have to resort to small-scale models. In this regard, large-eddy simulation (LES) equations result from filtering the NS equations in space. The effect of the under-resolved scales is then given by the subgrid stress (SGS) tensor that depends on both the filtered and the unfiltered velocity. Then, the famous closure problem in LES basically consists of approximating the SGS tensor with a tensor in terms of the (resolved) filtered velocity. In this way, the dynamical complexity of the NS equations is significantly reduced, resulting in a new set of PDE that are more amenable to being numerically solved on a coarse mesh. Over the past decades, the field of LES has drastically evolved together with the never-ending growth of computational capacity, gaining interest for a wider and wider range of applications. In this context, the objective of this Special Issue of Energies is to bring together people working on advanced, cutting-edge methods for the LES of turbulent flows but also on applications where LES techniques are allowing one to explore new frontiers. The scope includes, but is not limited to the following:

  • LES fundamentals;
  • Numerical methods for LES;
  • Wall-modeling techniques;
  • Hybrid RANS-LES methods;
  • Heat and mass transfer problems;
  • Multiphase flows;
  • Combustion;
  • Environmental and geophysical applications;
  • Industrial applications.

Prof. Dr. Assensi Oliva
Prof. Dr. F. Xavier Trias
Guest Editors

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Keywords

  • Turbulence
  • Large-eddy simulation
  • Turbulence modeling
  • Subgrid-scale model
  • Computational fluid dynamics
  • Wall modeling
  • Hybrid RANS-LES

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Published Papers (2 papers)

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Research

14 pages, 4976 KiB  
Article
Effect of Mixed-Flow Fans with a Newly Shaped Diffuser on Heat Stress of Dairy Cows Based on CFD
by Chunxia Yao, Zhengxiang Shi, Yang Zhao and Tao Ding
Energies 2019, 12(22), 4315; https://doi.org/10.3390/en12224315 - 12 Nov 2019
Cited by 4 | Viewed by 3049
Abstract
Mixed-flow fans (MFF) are widely used to reduce the heat stress in dairy cows in summer. Our research team developed MFFs with a newly shaped diffuser with the length of 250 mm and the circumferential angle of 150°, which have better performance in [...] Read more.
Mixed-flow fans (MFF) are widely used to reduce the heat stress in dairy cows in summer. Our research team developed MFFs with a newly shaped diffuser with the length of 250 mm and the circumferential angle of 150°, which have better performance in terms of maximum flow flux and energy efficiency. However, how the elevation angle of the diffuser influences the performance of MFFs and how the optimal fan perform in the field experiment has not been studied yet. In this paper, the diffuser was optimized by CFD (Computational Fluid Dynamics) simulation of the fan and a laboratory prototype test. An orthogonal test showed no interaction among length, circumferential angle, and elevation angle. The diffuser with an elevation angle of 10° performed better than that with an elevation angle of 0°, showing increased jet lengths, flow flux, and energy efficiency by 0.5 m, 0.69%, and 1.39%, respectively, and attaining greater axial wind speeds and better non-uniformity coefficients at the dairy cattle height. Then, through on-site controlled trials, we found that the 10°/150°/250 mm diffusers increased the overall average wind speeds by 9.4% with respect to the MFFs without a diffuser. MFFs with the newly shaped diffuser were used for field tests, and their effectiveness in alleviating heat stress in dairy cows was evaluated by testing environmental parameters and dairy cows’ physiological indicators. Although the temperature–humidity indexes (THIs) in the experimental barn with the optimized fan at different times were lower than those in the controlled barn, the environmental conditions corresponded to moderate heat stress. However, this was not consistent with cow’s respiratory rate and rectal temperature. Finally, on the basis of the CFD simulation of a dairy cow barn, the equivalent temperature of cattle (ETIC), which takes into account the effect of air velocity, showed that the environment caused moderate heat stress only at 13:00, but not at other times of the day. This shows that ETIC is more accurate to evaluate heat stress. Full article
(This article belongs to the Special Issue Large-Eddy Simulations of Turbulent Flows)
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20 pages, 13748 KiB  
Article
Numerical Investigation of Flow through a Valve during Charge Intake in a DISI -Engine Using Large Eddy Simulation
by Kaushal Nishad, Florian Ries, Yongxiang Li and Amsini Sadiki
Energies 2019, 12(13), 2620; https://doi.org/10.3390/en12132620 - 8 Jul 2019
Cited by 16 | Viewed by 4733
Abstract
Apart from electric vehicles, most internal combustion (IC) engines are powered while burning petroleum-based fossil or alternative fuels after mixing with inducted air. Thereby the operations of mixing and combustion evolve in a turbulent flow environment created during the intake phase and then [...] Read more.
Apart from electric vehicles, most internal combustion (IC) engines are powered while burning petroleum-based fossil or alternative fuels after mixing with inducted air. Thereby the operations of mixing and combustion evolve in a turbulent flow environment created during the intake phase and then intensified by the piston motion and influenced by the shape of combustion chamber. In particular, the swirl and turbulence levels existing immediately before and during combustion affect the evolution of these processes and determine engine performance, noise and pollutant emissions. Both the turbulence characteristics and the bulk flow pattern in the cylinder are strongly affected by the inlet port and valve design. In the present paper, large eddy simulation (LES) is appraised and applied to studying the turbulent fluid flow around the intake valve of a single cylinder IC-engine as represented by the so called magnetic resonance velocimetry (MRV) flow bench configuration with a relatively large Reynolds number of 45,000. To avoid an intense mesh refinement near the wall, various subgrid scale models for LES; namely the Smagorinsky, wall adapting local eddy (WALE) model, SIGMA, and dynamic one equation models, are employed in combination with an appropriate wall function. For comparison purposes, the standard RANS (Reynolds-averaged Navier–Stokes) k- ε model is also used. In terms of a global mean error index for the velocity results obtained from all the models, at first it turns out that all the subgrid models show similar predictive capability except the Smagorinsky model, while the standard k- ε model experiences a higher normalized mean absolute error (nMAE) of velocity once compared with MRV data. Secondly, based on the cost-accuracy criteria, the WALE model is used with a fine mesh of ≈39 millions control volumes, the averaged velocity results showed excellent agreement between LES and MRV measurements, revealing the high prediction capability of the suggested LES tool for valve flows. Thirdly, the turbulent flow across the valve curtain clearly featured a back flow resulting in a high speed intake jet in the middle. Comprehensive LES data are generated to carry out statistical analysis in terms of (1) evolution of the turbulent morphology across the valve passage relying on the flow anisotropy map, (2) integral turbulent scales along the intake-charge stream, (3) turbulent flow properties such as turbulent kinetic energy, turbulent velocity and its intensity within the most critical zone in intake-port and along the port length, it further transpires that the most turbulence are generated across the valve passage and these are responsible for the in-cylinder turbulence. Full article
(This article belongs to the Special Issue Large-Eddy Simulations of Turbulent Flows)
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