Special Issue "Large Eddy Simulation and Turbulence Modeling"

A special issue of Journal of Marine Science and Engineering (ISSN 2077-1312). This special issue belongs to the section "Physical Oceanography".

Deadline for manuscript submissions: closed (15 October 2020).

Special Issue Editor

Dr. Unai Fernandez-Gamiz
E-Mail Website
Guest Editor
Nuclear Engineering and Fluid Mechanics Department, University of the Basque Country UPV/EHU, 01006 Vitoria-Gasteiz, Araba, Spain
Interests: fluid mechanics; modeling and simulation; computational fluid dynamics; flow control; aerodynamics; offshore renewable energy (ORE) such as off-shore wind turbines or wave energy converters (WEC); oscillating water column (OWC) devices; hydrodynamics and dynamics of floating bodies under the presence of ocean waves; optimization of passive flow control systems (e.g., vortex generators, moving flaps, gurney flaps or microtabs); heat transfer; internal combustion; cooling systems; complex geometries; turbomachinery flows
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Special Issue Information

Dear Colleagues,

Computational power has been improved over the last few decades; therefore, complex flow modeling phenomena using computational fluid dynamics (CFD) have become more feasible. Furthermore, the improvement of computational power is expected to continue and will serve to progress in the CFD modeling capabilities.

The role of turbulence is essential to the understanding, prediction, and improvement of complex flows. In fact, turbulence is vital to the proper operation of many industrial applications. Generally, the goal of turbulence modeling is to reproduce the physics of the flow as accurately as possible with as little computational effort as possible. In some cases, turbulence is modeled by the Reynolds Averaged Navier–Stokes (RANS) methods, where the Navier–Stokes equations are ensemble averaged. This averaging results in an extra stress term, which is typically modeled with an effective turbulent viscosity. The ensemble averaging tends to remove the unsteady part of the turbulent flow. RANS models generally perform satisfactorily in less complex flows. Nevertheless, in more complex, highly time-dependent flows, the averaging tends to smear out essential structures in the flow field and consequently may be inappropriate.

A completely different approach from RANS modeling is large eddy simulation (LES). The fundamental idea of LES is that large-scale energy-containing eddies vary in different flows, while the small scales are more universal. The large-scale eddies are solved directly in the LES approach, while the effects of smaller-scale eddies are modeled. LES is typically computationally less expensive than direct numerical simulations (DNS) and, of course, computationally more expensive than RANS models. The most important reason is that conventional LES requires more scales of turbulence to be resolved than RANS models. Therefore, grids designed for LES simulations are typically denser than RANS grids and less dense than DNS grids. However, thanks to the current advances in computational power, large grids and therefore LES for complex engineering flows have become feasible and very useful.

The purpose of the current Special Issue is to publish the most exciting research with respect to the above subjects and to spread the articles freely for research, teaching, and reference purposes.

Dr. Unai Fernandez-Gamiz
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Journal of Marine Science and Engineering is an international peer-reviewed open access monthly journal published by MDPI.

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Keywords

  • aerodynamics
  • hydrodynamics
  • flow control
  • vortex modeling
  • large eddy simulation (LES)
  • turbulence modeling
  • computational fluid dynamics (CFD)
  • heat transfer
  • cooling systems
  • complex flows
  • coherent structures

Published Papers (4 papers)

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Research

Article
Accuracy of the Cell-Set Model on a Single Vane-Type Vortex Generator in Negligible Streamwise Pressure Gradient Flow with RANS and LES
J. Mar. Sci. Eng. 2020, 8(12), 982; https://doi.org/10.3390/jmse8120982 - 02 Dec 2020
Cited by 1 | Viewed by 490
Abstract
Passive flow control devices are included in the design of wind turbine blades in order to obtain better performance and reduce loads without consuming any external energy. Vortex Generators are one of the most popular flow control devices, whose main objective is to [...] Read more.
Passive flow control devices are included in the design of wind turbine blades in order to obtain better performance and reduce loads without consuming any external energy. Vortex Generators are one of the most popular flow control devices, whose main objective is to delay the flow separation and increase the maximum lift coefficient. Computational Fluid Dynamics (CFD) simulations of a Vortex Generator (VG) on a flat plate in negligible streamwise pressure gradient conditions with the fully-resolved mesh model and the cell-set model using Large Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS) were carried out, with the objective of evaluating the accuracy of the cell-set model taking the fully-resolved mesh model as benchmark. The implementation of the cell-set model entailed a considerable reduction of the number of cells, which entailed saving simulation time and resources. The coherent structures, vortex path, wall shear stress and size, strength and velocity profiles of the primary vortex have been analyzed. The results show good agreements between the fully-resolved mesh model and the cell-set mode with RANS in all the analyzed parameters. With LES, acceptable results were obtained in terms of coherent structures, vortex path and wall shear stress, but slight differences between models are visible in the size, strength and velocity profiles of the primary vortex. As this is considered the first application of the cell-set model on VGs, further research is proposed, since the implementation of the cell-set model can represent an advantage over the fully-resolved mesh model. Full article
(This article belongs to the Special Issue Large Eddy Simulation and Turbulence Modeling)
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Article
Performance Assessment of Three Turbulence Models Validated through an Experimental Wave Flume under Different Scenarios of Wave Generation
J. Mar. Sci. Eng. 2020, 8(11), 881; https://doi.org/10.3390/jmse8110881 - 05 Nov 2020
Cited by 1 | Viewed by 603
Abstract
This study aimed to adjust the turbulence models to the real behavior of the numerical wave flume (NWF) and the future research that will be carried out on it, according to the turbulence model that best adjusts to each particular case study. The [...] Read more.
This study aimed to adjust the turbulence models to the real behavior of the numerical wave flume (NWF) and the future research that will be carried out on it, according to the turbulence model that best adjusts to each particular case study. The k-ε, k-ω and large-eddy simulation (LES) models, using the volume of fluid (VOF) method, were analyzed and compared respectively. The wavemaker theory was followed to faithfully reproduce the waves, which were measured in an experimental wave flume (EWF) and compared with the theory to validate each turbulence model. Besides, reflection was measured with the Mansard and Funke method, which has shown promising results when studying one of the most critical turbulent behaviors in the wave flume, called the breaking of the waves. The free surface displacement obtained with each turbulence model was compared with the recorded signals located at three points of the experimental wave flume, in the time domain of each run, respectively. Finally, the calculated reflection coefficients and the amplitudes of the reflected waves were compared, aiming to have a better understanding of the wave reflection process at the extinction zone. The research showed good agreement between all the experimental signals and the numerical outcomes for all the turbulence models analyzed. Full article
(This article belongs to the Special Issue Large Eddy Simulation and Turbulence Modeling)
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Article
Large Eddy Simulation of Microbubble Drag Reduction in Fully Developed Turbulent Boundary Layers
J. Mar. Sci. Eng. 2020, 8(7), 524; https://doi.org/10.3390/jmse8070524 - 16 Jul 2020
Viewed by 662
Abstract
Microbubble drag reduction has good application prospects. It operates by injecting a large number of bubbles with tiny diameters into a turbulent boundary layer. However, its mechanism is not yet fully understood. In this paper, the mechanisms of microbubble drag reduction in a [...] Read more.
Microbubble drag reduction has good application prospects. It operates by injecting a large number of bubbles with tiny diameters into a turbulent boundary layer. However, its mechanism is not yet fully understood. In this paper, the mechanisms of microbubble drag reduction in a fully developed turbulent boundary layer over a flat-plate is investigated using a two-way coupled Euler-Lagrange approach based on large eddy simulation. The results show good agreement with theoretical values in the velocity distribution and the distribution of fluctuation intensities. As the results show, the presence of bubbles reduces the frequency of bursts associated with the sweep events from 637.8 Hz to 611.2 Hz, indicating that the sweep events, namely the impacting of high-speed fluids on the wall surface, are suppressed and the streamwise velocity near the wall is decreased, hence reducing the velocity gradient at the wall and consequently lessening the skin friction. The suppression on burst frequency also, with the fluid fluctuation reduced in degree, decreases the intensity of vortices near the wall, leading to reduced production of turbulent kinetic energy. Full article
(This article belongs to the Special Issue Large Eddy Simulation and Turbulence Modeling)
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Article
Wall-Resolved LES Modeling of a Wind Turbine Airfoil at Different Angles of Attack
J. Mar. Sci. Eng. 2020, 8(3), 212; https://doi.org/10.3390/jmse8030212 - 19 Mar 2020
Cited by 2 | Viewed by 684
Abstract
Noise has arisen as one of the main restrictions for the deployment of wind turbines in urban environments or in sensitive ecosystems like oceans for offshore and coastal applications. An LES model, adequately planned and resolved, is useful to describe the noise generation [...] Read more.
Noise has arisen as one of the main restrictions for the deployment of wind turbines in urban environments or in sensitive ecosystems like oceans for offshore and coastal applications. An LES model, adequately planned and resolved, is useful to describe the noise generation mechanisms in wind turbine airfoils. In this work, a wall-resolved LES model of the turbulent flow around a typical wind turbine airfoil is presented and described in detail. The numerical results obtained have been validated with hot wire measurements in a wind tunnel. The description of the boundary layer over the airfoil provides an insight into the main noise generation mechanism, which is known to be the scattering of the vortical disturbances in the boundary layer into acoustic waves at the airfoil trailing edge. In the present case, 2D wave instabilities are observed in both suction and pressure sides, but these perturbations are diffused into a turbulent boundary layer prior to the airfoil trailing edge, so tonal noise components are not expected in the far-field noise propagation. The results obtained can be used as input data for the prediction of noise propagation to the far-field using a hybrid aeroacoustic model. Full article
(This article belongs to the Special Issue Large Eddy Simulation and Turbulence Modeling)
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