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Open AccessEditorial

Turbulence: Numerical Analysis, Modeling, and Simulation

by William Layton

Fluids 2018, 3(1), 17; https://doi.org/10.3390/fluids3010017 - 18 Feb 2018

Cited by 1 | Viewed by 2822

Abstract

The problem of accurate and reliable prediction of turbulent flows is a central and intractable challenge that crosses disciplinary boundaries. [...] Full article

(This article belongs to the Special Issue Turbulence: Numerical Analysis, Modelling and Simulation)

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22 pages, 31080 KiB

Open AccessArticle

Database of Near-Wall Turbulent Flow Properties of a Jet Impinging on a Solid Surface under Different Inclination Angles

by Florian Ries, Yongxiang Li, Martin Rißmann, Dario Klingenberg, Kaushal Nishad, Benjamin Böhm, Andreas Dreizler, Johannes Janicka and Amsini Sadiki

Fluids 2018, 3(1), 5; https://doi.org/10.3390/fluids3010005 - 02 Jan 2018

Cited by 15 | Viewed by 6820

Abstract

In the present paper, direct numerical simulation (DNS) and particle image velocimetry (PIV) have been applied complementarily in order to generate a database of near-wall turbulence properties of a highly turbulent jet impinging on a solid surface under different inclination angles. Thereby, the [...] Read more.

In the present paper, direct numerical simulation (DNS) and particle image velocimetry (PIV) have been applied complementarily in order to generate a database of near-wall turbulence properties of a highly turbulent jet impinging on a solid surface under different inclination angles. Thereby, the main focus is placed on an impingement angle of

45^{\circ}

, since it represents a good generic benchmark test case for a wide range of technical fluid flow applications. This specific configuration features very complex flow properties including the presence of a stagnation point, development of the shear boundary layer and strong streamline curvature. In particular, this database includes near-wall turbulence statistics along with mean and rms velocities, budget terms in the turbulent kinetic energy equation, anisotropy invariant maps, turbulent length/time scales and near-wall shear stresses. These properties are useful for the validation of near-wall modeling approaches in the context of Reynolds-averaged Navier–Stokes (RANS) and large-eddy simulations (LES). From this study, in which further impingement angles (

0^{\circ}

,

90^{\circ}

) have been considered in the experiments only, it turns out that (1) the production of turbulent kinetic energy appears negative at the stagnation point for an impingement angle other than

0^{\circ}

and is balanced predominantly by pressure-related diffusion, (2) quasi-coherent thin streaks with large characteristic time scales appear at the stagnation region, while the organization of the flow is predominantly toroidal further downstream, and (3) near-wall shear stresses are low at the stagnation region and intense in regions where the direction of the flow changes suddenly. Full article

(This article belongs to the Special Issue Turbulence: Numerical Analysis, Modelling and Simulation)

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493 KiB

Open AccessArticle

Improving Accuracy in α-Models of Turbulence through Approximate Deconvolution

by Argus A. Dunca

Fluids 2017, 2(4), 58; https://doi.org/10.3390/fluids2040058 - 27 Oct 2017

Cited by 1 | Viewed by 2699

Abstract

In this report, we present several results in the theory of

α

-models of turbulence with improved accuracy that have been developed in recent years. The

α

-models considered herein are the Leray-

α

model, the zeroth Approximate Deconvolution Model (ADM) turbulence model, [...] Read more.

In this report, we present several results in the theory of

α

-models of turbulence with improved accuracy that have been developed in recent years. The

α

-models considered herein are the Leray-

α

model, the zeroth Approximate Deconvolution Model (ADM) turbulence model, the modified Leray-

α

and the Navier–Stokes-

α

model. For all of the models from above, the accuracy is limited to

α^{2}

in smooth flow regions. Better accuracy requires decreasing the filter radius

α

, which, in turn, requires a smaller mesh width that will lead in the end to a higher computational cost. Instead, one can use approximate deconvolution (without decreasing the mesh size) to attain better accuracy. Such deconvolution methods have been considered recently in many studies that show the efficiency of this approach. For smooth flows, periodic boundary conditions and van Cittert deconvolution operator of order N, the expected accuracy is

α^{2 N + 2}

. In a bounded domain, such results are valid only in case special conditions are satisfied. In more general conditions, the author has recently proved that, in the case of the ADM, the expected accuracy of the finite element method with Taylor–Hood elements and Crank–Nicolson time stepping method is

Δ t^{2} + h^{2} + K^{N} α^{2}

, where the constant

K < 1

depends on the ratio

α / h

, which is assumed constant. In this study, we present the extension of the result to the rest of the models. Full article

(This article belongs to the Special Issue Turbulence: Numerical Analysis, Modelling and Simulation)

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824 KiB

Open AccessArticle

Non-Iterative Partitioned Methods for Uncoupling Evolutionary Groundwater–Surface Water Flows

by Michaela Kubacki and Hoang Tran

Fluids 2017, 2(3), 47; https://doi.org/10.3390/fluids2030047 - 10 Sep 2017

Cited by 2 | Viewed by 3183

Abstract

We present an overview of a modern, efficient approach for uncoupling groundwater–surface water flows governed by the fully evolutionary Stokes–Darcy equations. Referred to as non-iterative partitioned methods, these algorithms treat the coupling terms explicitly and at each time level require only one Stokes [...] Read more.

We present an overview of a modern, efficient approach for uncoupling groundwater–surface water flows governed by the fully evolutionary Stokes–Darcy equations. Referred to as non-iterative partitioned methods, these algorithms treat the coupling terms explicitly and at each time level require only one Stokes and one Darcy sub-physics solve, thus taking advantage of existing solvers optimized for each sub-flow. This strategy often results in a time-step condition for stability. Furthermore, small problem parameters, specifically those related to the physical characteristics of the porous media domain, can render certain time-step conditions impractical. Despite these obstacles, researchers have made significant progress towards efficient, stable, and accurate partitioned methods. Herein, we provide a comprehensive survey and comparison of recent developments utilizing these non-iterative numerical schemes. Full article

(This article belongs to the Special Issue Turbulence: Numerical Analysis, Modelling and Simulation)

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1733 KiB

Open AccessArticle

Lagrangian Modeling of Turbulent Dispersion from Instantaneous Point Sources at the Center of a Turbulent Flow Channel

by Quoc Nguyen, Samuel E. Feher and Dimitrios V. Papavassiliou

Fluids 2017, 2(3), 46; https://doi.org/10.3390/fluids2030046 - 08 Sep 2017

Cited by 6 | Viewed by 4615

Abstract

The paper is focused on the simulation and modeling of the dispersion from an instantaneous source of heat or mass located at the center of a turbulent flow channel. The flow is modeled with a direct numerical simulation, and the dispersion is modeled [...] Read more.

The paper is focused on the simulation and modeling of the dispersion from an instantaneous source of heat or mass located at the center of a turbulent flow channel. The flow is modeled with a direct numerical simulation, and the dispersion is modeled with Lagrangian methods based on Lagrangian scalar tracking (LST). The LST technique allows the simulation of scalar sources that span a range of Prandtl or Schmidt numbers that cover orders of magnitude. The trajectories of individual heat or mass markers are tracked, generating a probability distribution function that describes the behavior of instantaneous point sources of a scalar in the turbulent field. The effect of the Prandtl or Schmidt number on turbulent dispersion is examined, with emphasis on the dispersion pattern. Results for Prandtl or Schmidt numbers between 0.1 and 15,000 are presented. For an instantaneous source at the channel center, it is found that there are two zones of cloud development: one where molecular diffusion plays a role at very small times (early stage of the dispersion), and one where turbulent convection dominates. The asphericity of the scalar marker cloud is found to increase monotonically, in contrast to published results for isotropic, homogenous turbulence, where the asphericity goes through a maximum. Full article

(This article belongs to the Special Issue Turbulence: Numerical Analysis, Modelling and Simulation)

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1403 KiB

Open AccessArticle

The Reduced NS-α Model for Incompressible Flow: A Review of Recent Progress

by Abigail L. Bowers and Leo G. Rebholz

Fluids 2017, 2(3), 38; https://doi.org/10.3390/fluids2030038 - 06 Jul 2017

Cited by 5 | Viewed by 3576

Abstract

This paper gives a review of recent results for the reduced Navier–Stokes-α (rNS-α) model of incompressible flow. The model was recently developed as a numerical approximation to the well known Navier–Stokes-α model, for the purpose of more efficiently computations in the C⁰ [...] Read more.

This paper gives a review of recent results for the reduced Navier–Stokes-α (rNS-α) model of incompressible flow. The model was recently developed as a numerical approximation to the well known Navier–Stokes-α model, for the purpose of more efficiently computations in the C⁰finite element setting. Its performance in initial numerical tests was remarkable, which led to analytical studies and further numerical tests, all of which provided excellent results. This paper reviews the main results established thus far for rNS-α, and presents some open problems for future work. Full article

(This article belongs to the Special Issue Turbulence: Numerical Analysis, Modelling and Simulation)

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2395 KiB

Open AccessArticle

Turbulence Intensity and the Friction Factor for Smooth- and Rough-Wall Pipe Flow

by Nils T. Basse

Fluids 2017, 2(2), 30; https://doi.org/10.3390/fluids2020030 - 10 Jun 2017

Cited by 36 | Viewed by 6831

Abstract

Turbulence intensity profiles are compared for smooth- and rough-wall pipe flow measurements made in the Princeton Superpipe. The profile development in the transition from hydraulically smooth to fully rough flow displays a propagating sequence from the pipe wall towards the pipe axis. The [...] Read more.

Turbulence intensity profiles are compared for smooth- and rough-wall pipe flow measurements made in the Princeton Superpipe. The profile development in the transition from hydraulically smooth to fully rough flow displays a propagating sequence from the pipe wall towards the pipe axis. The scaling of turbulence intensity with Reynolds number shows that the smooth- and rough-wall level deviates with increasing Reynolds number. We quantify the correspondence between turbulence intensity and the friction factor. Full article

(This article belongs to the Special Issue Turbulence: Numerical Analysis, Modelling and Simulation)

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10829 KiB

Open AccessArticle

High Wavenumber Coherent Structures in Low Re APG-Boundary-Layer Transition Flow—A Numerical Study

by Weijia Chen and Edmond Y. Lo

Fluids 2017, 2(2), 21; https://doi.org/10.3390/fluids2020021 - 28 Apr 2017

Cited by 1 | Viewed by 3671

Abstract

This paper presents a numerical study of high wavenumber coherent structure evolution in boundary layer transition flow using recently-developed high order Combined compact difference schemes with non-uniform grids in the wall-normal direction for efficient simulation of such flows. The study focuses on a [...] Read more.

This paper presents a numerical study of high wavenumber coherent structure evolution in boundary layer transition flow using recently-developed high order Combined compact difference schemes with non-uniform grids in the wall-normal direction for efficient simulation of such flows. The study focuses on a simulation of an Adverse-Pressure-Gradient (APG) boundary layer transition induced by broadband disturbance corresponding to the experiment of Borodulin et al. (Journal of Turbulence, 2006, 7, pp. 1–30). The results support the experimental observation that although the coherent structures seen during transition to turbulence have asymmetric shapes and occur in a random pattern, their local evolutional behaviors are quite similar. Further calculated local wavelet spectra of these coherent structures are also very similar. The wavelet spectrum of the streamwise disturbance velocity demonstrates high wavenumber clusters at the tip and the rear parts of the Λ-vortex. Both parts are imbedded at the primary Λ-vortex stage and spatially coincide with the spike region and high shear layer. The tip part is associated with the later first ring-like vortex, while the rear part with the remainder of the Λ-vortex. These observations help to shed light on the generation of turbulence, which is dominated by high wavenumber coherent structures. Full article

(This article belongs to the Special Issue Turbulence: Numerical Analysis, Modelling and Simulation)

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18204 KiB

Open AccessArticle

Evolutionary Optimization of Colebrook’s Turbulent Flow Friction Approximations

by Dejan Brkić and Žarko Ćojbašić

Fluids 2017, 2(2), 15; https://doi.org/10.3390/fluids2020015 - 06 Apr 2017

Cited by 37 | Viewed by 6522

Abstract

This paper presents evolutionary optimization of explicit approximations of the empirical Colebrook’s equation that is used for the calculation of the turbulent friction factor (λ), i.e., for the calculation of turbulent hydraulic resistance in hydraulically smooth and rough pipes including the transient zone [...] Read more.

This paper presents evolutionary optimization of explicit approximations of the empirical Colebrook’s equation that is used for the calculation of the turbulent friction factor (λ), i.e., for the calculation of turbulent hydraulic resistance in hydraulically smooth and rough pipes including the transient zone between them. The empirical Colebrook’s equation relates the unknown flow friction factor (λ) with the known Reynolds number (R) and the known relative roughness of the inner pipe surface (ε/D). It is implicit in the unknown friction factor (λ). The implicit Colebrook’s equation cannot be rearranged to derive the friction factor (λ) directly, and therefore, it can be solved only iteratively [λ = f(λ, R, ε/D)] or using its explicit approximations [λ ≈ f(R, ε/D)], which introduce certain error compared with the iterative solution. The optimization of explicit approximations of Colebrook’s equation is performed with the aim to improve their accuracy, and the proposed optimization strategy is demonstrated on a large number of explicit approximations published up to date where numerical values of the parameters in various existing approximations are changed (optimized) using genetic algorithms to reduce maximal relative error. After that improvement, the computational burden stays unchanged while the accuracy of approximations increases in some of the cases very significantly. Full article

(This article belongs to the Special Issue Turbulence: Numerical Analysis, Modelling and Simulation)

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19506 KiB

Open AccessArticle

Resolution and Energy Dissipation Characteristics of Implicit LES and Explicit Filtering Models for Compressible Turbulence

by Romit Maulik and Omer San

Fluids 2017, 2(2), 14; https://doi.org/10.3390/fluids2020014 - 06 Apr 2017

Cited by 18 | Viewed by 5891

Abstract

Solving two-dimensional compressible turbulence problems up to a resolution of 16, 384², this paper investigates the characteristics of two promising computational approaches: (i) an implicit or numerical large eddy simulation (ILES) framework using an upwind-biased fifth-order weighted essentially non-oscillatory (WENO) reconstruction [...] Read more.

Solving two-dimensional compressible turbulence problems up to a resolution of 16, 384², this paper investigates the characteristics of two promising computational approaches: (i) an implicit or numerical large eddy simulation (ILES) framework using an upwind-biased fifth-order weighted essentially non-oscillatory (WENO) reconstruction algorithm equipped with several Riemann solvers, and (ii) a central sixth-order reconstruction framework combined with various linear and nonlinear explicit low-pass spatial filtering processes. Our primary aim is to quantify the dissipative behavior, resolution characteristics, shock capturing ability and computational expenditure for each approach utilizing a systematic analysis with respect to its modeling parameters or parameterizations. The relative advantages and disadvantages of both approaches are addressed for solving a stratified Kelvin-Helmholtz instability shear layer problem as well as a canonical Riemann problem with the interaction of four shocks. The comparisons are both qualitative and quantitative, using visualizations of the spatial structure of the flow and energy spectra, respectively. We observe that the central scheme, with relaxation filtering, offers a competitive approach to ILES and is much more computationally efficient than WENO-based schemes. Full article

(This article belongs to the Special Issue Turbulence: Numerical Analysis, Modelling and Simulation)

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Review

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3524 KiB

Open AccessReview

A Review of Time Relaxation Methods

by Sean Breckling, Monika Neda and Tahj Hill

Fluids 2017, 2(3), 40; https://doi.org/10.3390/fluids2030040 - 17 Jul 2017

Cited by 5 | Viewed by 3654

Abstract

The time relaxation model has proven to be effective in regularization of Navier–Stokes Equations. This article reviews several published works discussing the development and implementations of time relaxation and time relaxation models (TRMs), and how such techniques are used to improve the accuracy [...] Read more.

The time relaxation model has proven to be effective in regularization of Navier–Stokes Equations. This article reviews several published works discussing the development and implementations of time relaxation and time relaxation models (TRMs), and how such techniques are used to improve the accuracy and stability of fluid flow problems with higher Reynolds numbers. Several analyses and computational settings of TRMs are surveyed, along with parameter sensitivity studies and hybrid implementations of time relaxation operators with different regularization techniques. Full article

(This article belongs to the Special Issue Turbulence: Numerical Analysis, Modelling and Simulation)

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