Impact of Computational Domain Size in Simulations of Homogeneous Decaying Turbulence and Mixing Layers

Large-eddy simulations of temporally evolving turbulent mixing layers have been carried out. The effect of the initial conditions and the size of the computational box on the turbulent statistics and structures is examined in detail. A series of calculations was initialized using two different realizations of a spatially developing turbulent boundary-layer with their free streams moving in opposite directions. Computations initialized with mean flow plus random perturbations with prescribed moments were also conducted. In all cases, the initial transitional stage, from boundary-layer turbulence or random noise to mixing-layer turbulence, was followed by a self-similar period. The self-similar periods, however, differed considerably: the growth rates and turbulence intensities showed differences, and were affected both by the initial condition and by the computational domain size. In all simulations the presence of quasi-two-dimensional spanwise rollers was clear, together with ‘braid’ regions with quasi-streamwise vortices. The development of these structures, however, was different: if strong rollers were formed early (as in the cases initialized by random noise), a well-organized pattern persisted throughout the self-similar period. The presence of boundary layer turbulence, on the other hand, inhibited the growth of the inviscid instability, and delayed the formation of the roller–braid patterns. Increasing the domain size tended to make the flow more three-dimensional.

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Optimising the computational domain size in CFD simulations of tall buildings

Heliyon ◽

10.1016/j.heliyon.2021.e06723 ◽

2021 ◽

Vol 7 (4) ◽

pp. e06723

Author(s):

Yousef Abu-Zidan ◽

Priyan Mendis ◽

Tharaka Gunawardena

Keyword(s):

Tall Buildings ◽

Domain Size ◽

Computational Domain ◽

Cfd Simulations

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Multi-Objective Optimization of a Microturbine Compact Recuperator

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2836479 ◽

2008 ◽

Vol 130 (3) ◽

Cited By ~ 9

Author(s):

Diego Micheli ◽

Valentino Pediroda ◽

Stefano Pieri

Keyword(s):

Heat Transfer ◽

Three Dimensional ◽

Numerical Procedure ◽

Design Procedure ◽

Domain Size ◽

Multidisciplinary Optimization ◽

Computational Domain ◽

Surface Geometry ◽

Multi Objective ◽

Flux Boundary Conditions

An automatic approach for the multi-objective shape optimization of microgas turbine heat exchangers is presented. According to the concept of multidisciplinary optimization, the methodology integrates a CAD parametric model of the heat transfer surfaces, a three-dimensional meshing tool, and a CFD solver, all managed by a design optimization platform. The repetitive pattern of the surface geometry has been exploited to reduce the computational domain size, and the constant flux boundary conditions have been imposed to better suit the real operative conditions. A new approach that couples cold and warm fluids in a periodic unitary cell is introduced. The effectiveness of the numerical procedure was verified comparing the numerical results with available literature data. The optimization objectives are maximizing the heat transfer rate and minimizing both friction factor and heat transfer surface. The paper presents the results of the optimization of a 50kWMGT recuperator. The design procedure can be effectively extended and applied to any industrial heat exchanger application.

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Study of Wake Profiles of a Simplified Model of High Speed Train Using RANS and LES Turbulent Models

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.629.426 ◽

2014 ◽

Vol 629 ◽

pp. 426-430

Author(s):

Sufiah Mohd Salleh ◽

Mohamed Sukri Mat Ali ◽

Sheikh Ahmad Zaki Shaikh Salim ◽

Sallehuddin Muhamad ◽

Muhammad Iyas Mahzan

Keyword(s):

High Speed ◽

Large Scale ◽

Sudden Change ◽

Domain Size ◽

Recirculation Region ◽

Bluff Bodies ◽

Computational Domain ◽

High Speed Train ◽

Free Shear Layer ◽

Turbulent Models

Flow structure over bluff bodies is more complex in wake. The wake is characterized by the unsteady behavior of the flow, large scale turbulent structure and strong recirculation region. For the case of high speed train, wake can be observed at the gap between the coaches and also on the rear coach. Wakes formation of high speed train are generated by free shear layer that is originated from the flow separation due to the sudden change in geometry. RANS and LES turbulent models are used in this paper to stimulate the formation of wakes and behavior of the flow over a simplified high speed train model. This model consists of two coaches with the gap between them is 0.5D. A total of four simulations have been made to study the effect of computational domain size and grid resolution on wake profiles of a simplified high speed train. The result shows that the computational domain can be reduced by decreasing the ground distance to 1.5D without affecting the magnitude of the wake profile. Both RANS and LES can capture the formation of the wake, but LES requires further grid refinement as the results between the two grid resolutions are grid dependent.

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Computational investigation of turbulent jet impinging onto rotating disk

International Journal of Numerical Methods for Heat &amp Fluid Flow ◽

10.1108/09615530710730157 ◽

2007 ◽

Vol 17 (3) ◽

pp. 284-301 ◽

Cited By ~ 28

Author(s):

A.C. Benim ◽

K. Ozkan ◽

M. Cagan ◽

D. Gunes

Keyword(s):

Boundary Conditions ◽

Isotropic Turbulence ◽

Domain Size ◽

Rotating Disk ◽

Turbulent Jet ◽

Turbulence Structure ◽

Computational Domain ◽

Convergence Criteria ◽

Computational Investigation ◽

Content Type

PurposeThe main purpose of the paper is the validation of a broad range of RANS turbulence models, for the prediction of flow and heat transfer, for a broad range of boundary conditions and geometrical configurations, for this class of problems.Design/methodology/approachTwo‐ and three‐dimensional computations are performed using a general‐purpose CFD code based on a finite volume method and a pressure‐correction formulation. Special attention is paid to achieve a high numerical accuracy by applying second order discretization schemes and stringent convergence criteria, as well as performing sensitivity studies with respect to the grid resolution, computational domain size and boundary conditions. Results are assessed by comparing the predictions with the measurements available in the literature.FindingsA rather unsatisfactory performance of the Reynolds stress model is observed, in general, although the contrary has been expected in this rotating flow, exhibiting a predominantly non‐isotropic turbulence structure. The best overall agreement with the experiments is obtained by the k‐ω model, where the SST model is also observed to provide a quite good performance, which is close to that of the k‐ω model, for most of the investigated cases.Originality/valueTo date, computational investigation of turbulent jet impinging on to “rotating” disk has not received much attention. To the best of the authors' knowledge, a thorough numerical analysis of the generic problem comparable with present study has not yet been attempted.

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Statistical characteristics of turbulent mixing in spherical and cylindrical converging Richtmyer–Meshkov instabilities

Journal of Fluid Mechanics ◽

10.1017/jfm.2021.818 ◽

2021 ◽

Vol 928 ◽

Author(s):

Xinliang Li ◽

Yaowei Fu ◽

Changping Yu ◽

Li Li

Keyword(s):

Turbulent Mixing ◽

Initial Perturbation ◽

Great Influence ◽

Mixing Layers ◽

Statistical Characteristics ◽

Computational Domain ◽

Heavy Fluid ◽

Node Number ◽

Geometric Effect ◽

Atwood Number

In this paper, the Richtmyer–Meshkov instabilities in spherical and cylindrical converging geometries with a Mach number of approximately 1.5 are investigated by using the high resolution implicit large eddy simulation method, and the influence of the geometric effect on the turbulent mixing is investigated. The heavy fluid is sulphur hexafluoride (SF6), and the light fluid is nitrogen (N2). The shock wave converges from the heavy fluid into the light fluid. The Atwood number is 0.678. The total structured and uniform Cartesian grid node number in the main computational domain is 20483. In addition, to avoid the influence of boundary reflection, a sufficiently long sponge layer with 50 non-uniform coarse grids is added for each non-periodic boundary. Present numerical simulations have high and nonlinear initial perturbation levels, which rapidly lead to turbulent mixing in the mixing layers. Firstly, some physical-variable mean profiles, including mass fraction, Taylor Reynolds number, turbulent kinetic energy, enstrophy and helicity, are provided. Second, the mixing characteristics in the spherical and cylindrical turbulent mixing layers are investigated, such as molecular mixing fraction, efficiency Atwood number, turbulent mass-flux velocity and density self-correlation. Then, Reynolds stress and anisotropy are also investigated. Finally, the radial velocity, velocity divergence and enstrophy in the spherical and cylindrical turbulent mixing layers are studied using the method of conditional statistical analysis. Present numerical results show that the geometric effect has a great influence on the converging Richtmyer–Meshkov instability mixing layers.

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Effect of the spanwise computational domain size on the flow over a two-dimensional bluff body with spanwise periodic perturbations at low Reynolds number

Computers & Fluids ◽

10.1016/j.compfluid.2019.01.006 ◽

2019 ◽

Vol 183 ◽

pp. 102-106 ◽

Cited By ~ 1

Author(s):

Woojin Kim ◽

Haecheon Choi

Keyword(s):

Reynolds Number ◽

Bluff Body ◽

Low Reynolds Number ◽

Domain Size ◽

Computational Domain ◽

Two Dimensional ◽

Periodic Perturbations ◽

Low Reynolds

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An Unstructured Reacting Flow Solver With Coupled Implicit Solution of the Species Conservation Equations

Heat Transfer: Volume 3 ◽

10.1115/ht2008-56145 ◽

2008 ◽

Author(s):

Ankan Kumar ◽

Sandip Mazumder

Keyword(s):

Species Conservation ◽

Domain Size ◽

Reacting Flow ◽

Computational Domain ◽

Conservation Equations ◽

Flow Solver ◽

As Species ◽

Minimum Residual ◽

Volume Method ◽

Coupled Solution

Many reacting flow applications mandate coupled solution of the species conservation equations. A low-memory coupled solver was developed to solve the species transport equations on an unstructured mesh with implicit spatial as well as species-to-species coupling. First, the computational domain was decomposed into sub-domains comprised of geometrically contiguous cells—a process termed internal domain decomposition (IDD). This was done using the binary spatial partitioning (BSP) algorithm. Following this step, for each sub-domain, the discretized equations were developed using the finite-volume method, written in block implicit form, and solved using an iterative solver based on Krylov sub-space iterations, i.e., the Generalized Minimum Residual (GMRES) solver. Overall (outer) iterations were then performed to treat explicitness at sub-domain interfaces and non-linearities in the governing equations. The solver is demonstrated for a laminar ethane-air flame calculation with five species and a single reaction step, and for a catalytic methane-air combustion case with 19 species and 22 reaction steps. It was found that the best performance is manifested for sub-domain size of about 1000 cells, the exact number depending on the problem at hand. The overall gain in computational efficiency was found to be a factor of 2–5 over the block Gauss-Seidel procedure.

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